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.wd-entry-content{max-width:1200px!important}.sr-ct-2026{max-width:1200px}}\n@media (max-width:900px){.sr-author-grid{grid-template-columns:1fr;gap:0}.sr-ct-dev__grid{grid-template-columns:1fr}.sr-ct-dev__col+.sr-ct-dev__col{border-left:0;border-top:1px solid var(--rule)}.sr-ct-rels{grid-template-columns:1fr 1fr}.sr-final-cta{grid-template-columns:1fr;gap:24px}.sr-ct-ladder__bar{grid-template-columns:repeat(2,1fr);gap:3px 18px}.sr-ct-rung--3,.sr-ct-rung--4{margin-top:16px}}\n@media (max-width:640px){.sr-ct-2026{font-size:18px;padding:0 0 60px}.sr-byline__author{width:100%;align-items:center;flex-wrap:wrap;gap:6px 10px}.sr-byline b{white-space:nowrap}.sr-byline{gap:12px 18px}.sr-ct-badge__x{display:none}.sr-ct-band{padding:28px 20px 26px}.sr-ct-2026 .sr-ct-step{grid-template-columns:44px minmax(0,1fr);gap:0 12px;padding:18px 0}.sr-ct-step__n{margin-left:0}.sr-ct-2026 .sr-ct-step:after{left:15px}.sr-ct-step__t{grid-column:2;text-align:left;padding-top:10px}.sr-ct-step__h{font-size:16.5px}.sr-ct-rels{grid-template-columns:1fr}.sr-ct-txbody{padding:20px 18px 4px}.sr-ct-dev__col{padding:22px 20px}.sr-ct-dev__links{padding:16px 20px}.sr-ct-dev__links a{flex:1 1 auto;text-align:center}#quick-answer{padding:22px 20px 8px}#quick-answer p{font-size:18.5px}.sr-final-cta{padding:28px 20px 26px}.sr-ct-spec li{grid-template-columns:1fr;gap:2px}.sr-ct-play svg{width:62px;height:62px}}\n@media (prefers-reduced-motion:reduce){.sr-ct-2026 *,.sr-light-toc *{animation-duration:.001ms!important;animation-iteration-count:1!important;transition-duration:.001ms!important}}<\/style>\n<div class=\"sr-mast\">\n<p class=\"sr-deck\">One structure, one number, five minutes. The median nerve found among the flexor tendons by tilting the transducer, its cross-sectional area taken on the frozen frame, and that number read against a published cut-off.<\/p>\n<div class=\"sr-author-panel\" data-suresult-author-panel aria-label=\"Article authors\">\n<p class=\"sr-byline__label\">Written and clinically reviewed by<\/p>\n<div class=\"sr-author-grid\">\n<article class=\"sr-author-card\" data-sr-author=\"fernando-mariz-md\">\n<div class=\"sr-author-card__head\"><img src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/fernando-mariz-md-author-avatar.png\" alt=\"Fernando Mariz, MD\" width=\"42\" height=\"42\" loading=\"lazy\" decoding=\"async\"><span class=\"sr-author-card__id\"><b>Fernando Mariz, MD<\/b><span class=\"sr-author-card__role\">Gynecology, pelvic surgery, sonography<\/span><\/span><\/div>\n<details data-sr-author-bio>\n<summary>About Dr. Mariz<\/summary>\n<p>I am Dr. Fernando Mariz, a gynecology and pelvic surgery physician practicing in New York City. Before my medical career, I served in the U.S. Marine Corps, where I developed the discipline, focus, and steadiness that continue to shape the way I care for patients today. At Maiden Lane Medical, my work covers women&rsquo;s health, preventive care, sonography, pelvic pain, abnormal uterine bleeding, and minimally invasive gynecologic procedures.<\/p>\n<p class=\"sr-author-card__links\"><a href=\"https:\/\/maidenlanemedical.com\/profile\/fernando-mariz-md\/\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Maiden Lane Medical profile<\/a> &middot; <a href=\"https:\/\/weillcornell.org\/fernando-marizmd-9639\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Weill Cornell Medicine<\/a><\/p>\n<\/details>\n<\/article>\n<article class=\"sr-author-card\" data-sr-author=\"jailyn-avila-md\">\n<div class=\"sr-author-card__head\"><img src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/jailyn-avila-md-author-avatar.png\" alt=\"Jailyn Avila, MD\" width=\"42\" height=\"42\" loading=\"lazy\" decoding=\"async\"><span class=\"sr-author-card__id\"><b>Jailyn Avila, MD<\/b><span class=\"sr-author-card__role\">Emergency medicine, POCUS education<\/span><\/span><\/div>\n<details data-sr-author-bio>\n<summary>About Dr. Avila<\/summary>\n<p>I am Dr. Jailyn Avila, an emergency medicine physician, educator, and digital health innovator based in Southern California. My clinical work is rooted in emergency care, while my teaching focuses on point-of-care ultrasound, residency education, and practical training for physicians. Through my roles with Emergent Medical Associates, UHS SoCal MEC Emergency Medicine Residency, Core Ultrasound, and FemInEM, I work at the intersection of patient care, medical education, and accessible digital learning.<\/p>\n<p class=\"sr-author-card__links\"><a href=\"https:\/\/jailynavila.com\/\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">Personal site<\/a> &middot; <a href=\"https:\/\/feminem.org\/about\" target=\"_blank\" rel=\"noopener noreferrer nofollow\">FemInEM<\/a><\/p>\n<\/details>\n<\/article>\n<\/div>\n<p class=\"sr-author-meta\"><span class=\"sr-verified-badge\">Verified authors<\/span><span>Updated <b>September 5, 2026<\/b><\/span><\/p>\n<\/div>\n<\/div>\n<figure class=\"sr-ct-stage\">\n<button class=\"sr-ct-player\" id=\"sr-ct-player\" type=\"button\" aria-label=\"Play the five-minute median nerve walkthrough\"><br \/>\n<img src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/carpal-tunnel-median-nerve-anisotropy-poster.jpg\" alt=\"Live transverse ultrasound of the anterior wrist on a Suresult D3Ultra showing the flexor tendons and the median nerve among them, MSK preset at 20 mm depth\" width=\"1280\" height=\"720\" fetchpriority=\"high\" decoding=\"async\"><br \/>\n<span class=\"sr-ct-play\"><svg viewBox=\"0 0 84 84\" aria-hidden=\"true\" focusable=\"false\"><circle cx=\"42\" cy=\"42\" r=\"40\" fill=\"rgba(10,14,18,.62)\" stroke=\"rgba(255,255,255,.9)\" stroke-width=\"1.6\"\/><path d=\"M34.5 28.2 L58 42 L34.5 55.8 Z\" fill=\"#fff\"\/><\/svg><\/span><br \/>\n<span class=\"sr-ct-badge\"><span>5:27<\/span><span class=\"sr-ct-badge__k\">10 key moments<\/span><span class=\"sr-ct-badge__x\">Transcript below<\/span><\/span><br \/>\n<\/button><figcaption class=\"sr-ct-cap\"><b>Published on the Suresult channel on 13 October 2025.<\/b> Runtime 5:27. Every timestamp on this page is on the YouTube clock, and every one of them jumps the player.<\/figcaption><\/figure>\n<section id=\"quick-answer\">\n<h2>Quick answer<\/h2>\n<p><strong>A carpal tunnel ultrasound is one measurement: the cross-sectional area of the median nerve, taken in transverse at the wrist, where the nerve is at its widest.<\/strong> You find the nerve by tilting the transducer until the flexor tendons darken and drop out of the image and the nerve does not, freeze on the largest cross-section, and take the area with the ellipse or the trace tool. Published cut-offs cluster between 8.5 and 10 mm&sup2; at the carpal tunnel inlet, and the AANEM rates the measurement as an accurate diagnostic test for carpal tunnel syndrome at its highest evidence level. The scan on this page runs the whole sequence in five minutes on a general-purpose transducer, with the operator saying on camera exactly what a higher-frequency probe would have bought him. My advice on a first watch: take 1:40 to 3:10 end to end &mdash; that is the identification and the measurement, and everything else on the page hangs off those ninety seconds.<\/p>\n<p class=\"sr-answer-note\">Looking for hardware rather than the exam? The <a href=\"https:\/\/suresultmed.com\/specialty\/handheld-ultrasound-for-musculoskeletal-msk-medicine\/\">musculoskeletal hub<\/a> compares the models used for nerve and small-parts work, and the <a href=\"https:\/\/suresultmed.com\/shop\/handheld-ultrasounds\/d3ultra-multipurpose-handheld-ultrasound\/\">D3Ultra product page<\/a> carries the full specification and current price.<\/p>\n<\/section>\n<section id=\"decision-chain\">\n<div class=\"sr-ct-band\">\n<p class=\"sr-ct-band__eye\">The decision chain<\/p>\n<h2>Five moves from a wrist to a number<\/h2>\n<p class=\"sr-ct-band__sub\">This scan is not a tour of anatomy. It is one structure and a short chain of decisions, each of which has to hold for the next one to mean anything. Click any step to jump the recording to it.<\/p>\n<div class=\"sr-ct-chain\"><a class=\"sr-ct-step\" href=\"#t=100\" data-sr-seek=\"100\"><span class=\"sr-ct-step__n\">01<\/span><span class=\"sr-ct-step__b\"><span class=\"sr-ct-step__k\">Separate<\/span><span class=\"sr-ct-step__h\">Tilt until the tendons disappear<\/span><span class=\"sr-ct-step__q\">In cross-section a nerve and a tendon look alike. Tilting the transducer settles it: tendons are far more sensitive to anisotropy and darken off-axis, so the structure still visible at an angle is the nerve.<\/span><span class=\"sr-ct-step__c\"><i>anisotropy<\/i><i>tilt on and off axis<\/i><i>B-mode<\/i><\/span><\/span><span class=\"sr-ct-step__t\">1:40<\/span><\/a><a class=\"sr-ct-step\" href=\"#t=145\" data-sr-seek=\"145\"><span class=\"sr-ct-step__n\">02<\/span><span class=\"sr-ct-step__b\"><span class=\"sr-ct-step__k\">Maximise<\/span><span class=\"sr-ct-step__h\">Sweep for the widest point<\/span><span class=\"sr-ct-step__q\">The area you measure is only meaningful if it is the largest one. A short proximal-to-distal sweep finds it, and the frame is frozen there rather than wherever the probe happened to stop.<\/span><span class=\"sr-ct-step__c\"><i>proximal to distal<\/i><i>freeze on the maximum<\/i><\/span><\/span><span class=\"sr-ct-step__t\">2:25<\/span><\/a><a class=\"sr-ct-step\" href=\"#t=170\" data-sr-seek=\"170\"><span class=\"sr-ct-step__n\">03<\/span><span class=\"sr-ct-step__b\"><span class=\"sr-ct-step__k\">Measure<\/span><span class=\"sr-ct-step__h\">Ellipse, or trace it by hand<\/span><span class=\"sr-ct-step__q\">Two of the six tools in the measurement menu return an area. The ellipse is faster; the trace follows a nerve that is not elliptical. Both are taken inside the hyperechoic rim, not around it.<\/span><span class=\"sr-ct-step__c\"><i>AREA\/CIRCUM<\/i><i>TRACE<\/i><\/span><\/span><span class=\"sr-ct-step__t\">2:50<\/span><\/a><a class=\"sr-ct-step\" href=\"#t=190\" data-sr-seek=\"190\"><span class=\"sr-ct-step__n\">04<\/span><span class=\"sr-ct-step__b\"><span class=\"sr-ct-step__k\">Decide<\/span><span class=\"sr-ct-step__h\">Read the area against a cut-off<\/span><span class=\"sr-ct-step__q\">One number, one comparison. The frozen frame here returns 0.08 cm\u00b2 \u2014 8 mm\u00b2, under every cut-off in common use, which is what a normal median nerve looks like.<\/span><span class=\"sr-ct-step__c\"><i>cross-sectional area<\/i><i>rule-out<\/i><\/span><\/span><span class=\"sr-ct-step__t\">3:10<\/span><\/a><a class=\"sr-ct-step\" href=\"#t=246\" data-sr-seek=\"246\"><span class=\"sr-ct-step__n\">05<\/span><span class=\"sr-ct-step__b\"><span class=\"sr-ct-step__k\">Confirm<\/span><span class=\"sr-ct-step__h\">Wiggle, then compare proximally<\/span><span class=\"sr-ct-step__q\">Two cheap manoeuvres when the number sits close to the line: fingers moving should carry the nerve with them, and a nerve that widens as it runs distally is doing the opposite of what a healthy one does.<\/span><span class=\"sr-ct-step__c\"><i>finger wiggle<\/i><i>proximal comparison<\/i><\/span><\/span><span class=\"sr-ct-step__t\">4:06<\/span><\/a><\/div>\n<div class=\"sr-ct-ladder\">\n<p class=\"sr-ct-ladder__h\">The confidence ladder, in his numbers<\/p>\n<div class=\"sr-ct-ladder__bar\"><span class=\"sr-ct-rung sr-ct-rung--1\"><b>9 mm&sup2;<\/b><em>his stated cut-off<\/em><\/span><span class=\"sr-ct-rung sr-ct-rung--2\"><b>11 mm&sup2;<\/b><em>more confident<\/em><\/span><span class=\"sr-ct-rung sr-ct-rung--3\"><b>12 mm&sup2;<\/b><em>\u201cover 12\u201d, in his words<\/em><\/span><span class=\"sr-ct-rung sr-ct-rung--4\"><b>13 mm&sup2;<\/b><em>no longer a close call<\/em><\/span><\/div>\n<\/div>\n<p class=\"sr-ct-band__note\">The ladder is the escalation the presenting clinician sets out at 3:32 &mdash; his point being that a value sitting just over a cut-off is a weaker call than one well past it. The threshold this page states in its own voice is the published one, and it is cited in Sources.<\/p>\n<\/div>\n<\/section>\n<section id=\"key-moments\">\n<p class=\"sr-ct-krow\">Timestamped<\/p>\n<h2>Key moments, with the settings<\/h2>\n<p>The third column is the part that usually goes missing from a scan video. Two things are worth noticing in it. The first is that the preset, the depth and the focus positions are set once, at 1:04, and never touched again &mdash; unlike a multi-window study, a nerve scan is one setup. The second is what the interface does <em>not<\/em> show: this recording has the parameter overlay switched off, so gain, dynamic range and transmit frequency are never displayed. The frequency ceiling is stated out loud instead, at 0:12.<\/p>\n<div class=\"sr-table-wrap\">\n<table class=\"sr-ct-km\">\n<colgroup>\n<col style=\"width:82px\">\n<col>\n<col style=\"width:280px\"><\/colgroup>\n<thead>\n<tr>\n<th>Time<\/th>\n<th>What is on screen<\/th>\n<th>Transducer, preset, on-screen state<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=0\" data-sr-seek=\"0\">0:00<\/a><\/td>\n<td><b>The probe you have, and the one you would rather have<\/b><span class=\"sr-ct-screen\">Carpal tunnel syndrome is framed as a compression neuropathy of the median nerve at the wrist. The presenting clinician states on camera that this unit tops out at 10 MHz and that 12, 15 or 18 MHz would resolve the nerve better \u2014 then makes the argument the rest of the recording has to earn: a general-purpose transducer is enough to make this call.<\/span><\/td>\n<td class=\"sr-ct-set\">SX-6CT \u00b7 MSK preset \u00b7 D 20 mm \u00b7 LIVE \u00b7 software V 3.6.74<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=36\" data-sr-seek=\"36\">0:36<\/a><\/td>\n<td><b>Positioning the wrist<\/b><span class=\"sr-ct-screen\">Gel is already on the transducer. The forearm laid flat on a table is the preferred setup; holding the arm works too, and is what he says he does most of the time, because the scan is short enough not to need the furniture.<\/span><\/td>\n<td class=\"sr-ct-set\">SX-6CT \u00b7 MSK preset \u00b7 D 20 mm \u00b7 LIVE<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=64\" data-sr-seek=\"64\">1:04<\/a><\/td>\n<td><b>Preset, focus, gain and depth<\/b><span class=\"sr-ct-screen\">The general musculoskeletal preset is selected \u2014 a dedicated nerve preset if the unit has one, MSK if not. Focus, gain and depth are named as the three things to set before you start looking, and on this recording they are set once and never touched again.<\/span><\/td>\n<td class=\"sr-ct-set\">MSK preset \u00b7 D 20 mm \u00b7 two focus markers at \u22484 mm and \u22489 mm \u00b7 rail: Gain+, Gain\u2212, Depth, Focus, Dyn., Harmonic, Denoise, B Mode<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=100\" data-sr-seek=\"100\">1:40<\/a><\/td>\n<td><b>Anisotropy: telling nerve from tendon<\/b><span class=\"sr-ct-screen\">The single most useful beat in the recording. The transducer is tilted back and forth across the flexor tendons and structures wink in and out of the image. Tendons are the sensitive ones; the nerve is not. The structure that stays visible through the tilt is the median nerve.<\/span><\/td>\n<td class=\"sr-ct-set\">SX-6CT \u00b7 MSK preset \u00b7 D 20 mm \u00b7 LIVE \u00b7 B-mode, no Doppler<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=145\" data-sr-seek=\"145\">2:25<\/a><\/td>\n<td><b>Finding the largest cross-section<\/b><span class=\"sr-ct-screen\">A short sweep proximal and distal looking for the point where the nerve is widest, then freeze. The structure that did not wink out on the tilt is identified on the frozen frame as the median nerve.<\/span><\/td>\n<td class=\"sr-ct-set\">MSK preset \u00b7 D 20 mm \u00b7 LIVE \u2192 FREEZE \u00b7 cine buffer 100\/100<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=170\" data-sr-seek=\"170\">2:50<\/a><\/td>\n<td><b>Ellipse or trace<\/b><span class=\"sr-ct-screen\">The measurement menu is opened over the frozen frame: LENGTH, AREA\/CIRCUM, TRACE, Depth, ANGLE, Area Ratio. Two of those six return a cross-sectional area \u2014 an ellipse fitted to the nerve, or an outline drawn around it by hand.<\/span><\/td>\n<td class=\"sr-ct-set\">FREEZE \u00b7 Meas \u25b8 AREA\/CIRCUM or TRACE<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=190\" data-sr-seek=\"190\">3:10<\/a><\/td>\n<td><b>Reading the number<\/b><span class=\"sr-ct-screen\">The closed trace returns AREA 0.08 cm\u00b2 on screen. The presenting clinician gives his own cut-off in the same breath: 0.09 cm\u00b2, which is 9 mm\u00b2, at close to full sensitivity and a specificity he puts in the high 80s to low 90s.<\/span><\/td>\n<td class=\"sr-ct-set\">FREEZE \u00b7 trace closed \u00b7 on-screen AREA 0.08 cm\u00b2<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=212\" data-sr-seek=\"212\">3:32<\/a><\/td>\n<td><b>When the number is well over the line<\/b><span class=\"sr-ct-screen\">The escalation, and the part most threshold tables leave out: a value a little over the cut-off is a weaker call than 11, 12 or 13 mm\u00b2. He names 12 mm\u00b2 as the point where he stops hedging.<\/span><\/td>\n<td class=\"sr-ct-set\">FREEZE \u00b7 measurement retained on screen<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=246\" data-sr-seek=\"246\">4:06<\/a><\/td>\n<td><b>Two confirmatory manoeuvres<\/b><span class=\"sr-ct-screen\">Ask the patient to wiggle their fingers and the nerve should shift with the tendons; one that stays put is a second sign. Then scan up to about 10 cm proximal and compare areas \u2014 a nerve should narrow as it runs distally, so an increase, which he puts at 40% or a factor of 1.4, points the other way.<\/span><\/td>\n<td class=\"sr-ct-set\">SX-6CT \u00b7 MSK preset \u00b7 D 20 mm \u00b7 LIVE<\/td>\n<\/tr>\n<tr>\n<td class=\"sr-ct-t\"><a href=\"#t=289\" data-sr-seek=\"289\">4:49<\/a><\/td>\n<td><b>The close, and a caption that disagrees with it<\/b><span class=\"sr-ct-screen\">The exam closes on the cut-off used as a rule-out. A burned-in caption then puts a second figure on screen \u2014 that 10 mm\u00b2 could be the better balance of sensitivity and specificity \u2014 next to two reference images captured on a different machine.<\/span><\/td>\n<td class=\"sr-ct-set\">Reference images and captions \u00b7 no live scanning<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p class=\"sr-table-note\">Transcribed from the device interface visible in the recording. Depth is read off the on-image scale, which is marked at 0, 5, 10 and 15 mm with the field ending at 20 mm; the two focus carets sit at roughly 4 mm and 9 mm. Software build V 3.6.74.<\/p>\n<\/section>\n<section id=\"what-it-shows\">\n<p class=\"sr-ct-krow\">Reading the images<\/p>\n<h2>What this scan shows<\/h2>\n<p>In a transverse view of the anterior wrist the median nerve is a speckled oval sitting superficially among the flexor tendons, and at first pass it looks like one of them. The separation is not a matter of shape but of behaviour. Tendons are strongly anisotropic: angle the transducer a few degrees off perpendicular and their fibrillar echoes reflect away from the probe and the tendon goes black. Nerves are far less sensitive to that. So the manoeuvre at 1:40 is the whole identification &mdash; rock the transducer back and forth and watch which structure refuses to disappear. That one is the nerve.<\/p>\n<p>Where you measure matters as much as what you measure. The area is taken at the carpal tunnel inlet, at the level of the pisiform, in a true transverse plane, and at the point along the tunnel where the nerve is widest &mdash; which is why the recording sweeps a short distance proximal and distal before freezing rather than measuring the first clean image it finds. On the frozen frame two of the six measurement tools return an area: an ellipse fitted to the nerve, or a trace drawn around it by hand. Every Class I study behind the AANEM guideline used direct tracing, and the outline goes inside the bright rim of the nerve, not around it. Trace the rim in and the number comes back inflated.<\/p>\n<figure class=\"sr-ct-fig\">\n<img src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/carpal-tunnel-median-nerve-measurement-tools.jpg\" alt=\"Measurement menu open on a Suresult D3Ultra over a frozen transverse wrist image, listing LENGTH, AREA\/CIRCUM, TRACE, Depth, ANGLE and Area Ratio\" width=\"1280\" height=\"720\" loading=\"lazy\" decoding=\"async\"><figcaption class=\"sr-ct-figcap\"><b>The measurement menu on the frozen frame, at 2:50.<\/b> Six tools; two of them return a cross-sectional area. AREA\/CIRCUM fits an ellipse, which is faster and works on most nerves; TRACE follows an outline that is not elliptical, which is what direct tracing means.<\/figcaption><\/figure>\n<p>Then there is the number itself, and this recording is a good example of why a page like this should not simply repeat one. Three different cut-offs appear on the same asset: 9 mm&sup2; spoken at 3:10, 10 mm&sup2; in the video description, and a burned-in caption near the end offering 10 mm&sup2; as the better balance of sensitivity and specificity. The literature explains the spread rather than settling it. A systematic review of 41 studies and 2,504 nerves put the mean inlet area in healthy people at 8.74 mm&sup2;, so any diagnostic threshold has to sit just above the top of the normal range &mdash; and the Class I studies behind the AANEM guideline used 8.5 to 10 mm&sup2;, while a meta-analysis of 3,995 wrists found 9 mm&sup2; the best single criterion at 87.3% sensitivity and 83.3% specificity. Read that spread the way it is meant to be read: a threshold is a dial between catching everything and calling too much, not a line in nature.<\/p>\n<p>Which is exactly why the two manoeuvres at 4:06 are worth the extra ten seconds when a number lands close to the line. Asking the patient to move their fingers should carry the nerve along with the tendons; a nerve tethered in a tight tunnel does not travel. And comparing the wrist against the mid-forearm turns one absolute number into a ratio, which is more forgiving of body size and of a hurried caliper. That ratio has a name and a figure in the literature &mdash; roughly 1.0 in asymptomatic volunteers, an average of 2.1 in patients, and a value of 1.4 catching every affected patient in the series that defined it.<\/p>\n<p>The last variable is the hardware, and the operator is unusually honest about it in the first thirty seconds. Nerve work is a resolution problem: fascicles are sub-millimetre, and 12, 15 or 18 MHz resolves them where 10 MHz gives you an oval. What 10 MHz does give you is enough to find the nerve, freeze on its widest point and take an area &mdash; which is the measurement the diagnosis actually turns on. That is a real distinction worth keeping straight when choosing a probe: the cheaper frequency costs you the texture inside the nerve, not the number around it.<\/p>\n<\/section>\n<section id=\"transcript\">\n<p class=\"sr-ct-krow\">Verbatim<\/p>\n<h2>Full transcript<\/h2>\n<details class=\"sr-ct-tx\" id=\"sr-ct-transcript\" data-sr-transcript=\"1\" open>\n<summary>Transcript &mdash; 5:27, 11 passages<\/summary>\n<div class=\"sr-ct-txbody\">\n<p class=\"sr-ct-txnote\"><span>Transcribed from the recording and edited for readability; square brackets mark an editorial clarification, and every timestamp jumps the video.<\/span><\/p>\n<section class=\"sr-ct-txsec\">\n<h3 class=\"sr-ct-txwin\">Setup<\/h3>\n<div class=\"sr-ct-txcol\">\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=0\" data-sr-seek=\"0\">0:00<\/a>[Introducing himself and the exam.] Today I\u2019d like to show you how to evaluate for carpal tunnel syndrome \u2014 a compression peripheral neuropathy of the median nerve at the wrist, or at the carpal tunnel. So ideally you\u2019re using as high a frequency probe as you have access to, a linear probe. But today I\u2019m going to actually use a Suresult D3Ultra, which is a dual-purpose probe and it only goes up to 10 megahertz. Now, ideally 12 megahertz is better, 15 megahertz is better, 18 megahertz is better \u2014 but use what you have. And I want to show that you can use a general-purpose probe to diagnose carpal tunnel syndrome.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=36\" data-sr-seek=\"36\">0:36<\/a>So I\u2019ve already applied gel to the transducer, and I have my patient in my preferred position. I find this position \u2014 if you can pull a table close by, or if you have a table in your office where the patient can just lay their arm down, that\u2019s best. Of course, this is such a quick and simple scan you could just hold their arm and scan, which is what I typically do. It\u2019s so quick and easy.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=64\" data-sr-seek=\"64\">1:04<\/a>Okay, so I have things set up and we can go. I like to use sort of the presets \u2014 general musculoskeletal preset. Sometimes your unit \u2014 I\u2019m not sure what unit you\u2019re using \u2014 may have a nerve preset, but even a general musculoskeletal preset should work. So, as you can see from what we\u2019re seeing, there\u2019s a heck of a lot going on, right? And of course you want to make sure your focus points are set correctly, the gain is set correctly and depth is set correctly, so you can get as best a picture as you can.<\/p>\n<\/div>\n<\/section>\n<section class=\"sr-ct-txsec\">\n<h3 class=\"sr-ct-txwin\">Finding the nerve<\/h3>\n<div class=\"sr-ct-txcol\">\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=100\" data-sr-seek=\"100\">1:40<\/a>So I\u2019m going back and forth here, and you\u2019ll see that there\u2019s so many structures. What the heck are we looking for? Well, as I tilt back and forth, things wink in and out of existence \u2014 this is an imaging artifact called anisotropy, and tendons are more sensitive than nerves. Now in cross-section a nerve and a tendon look very similar, but since nerves are less sensitive to anisotropy, the structure which is more persistent is going to be the nerve. So as I go back and forth, you\u2019ll see that there\u2019s one thing that looks like a tendon, just like the other tendons, but it doesn\u2019t go black as I tilt back and forth. And that\u2019s going to be the nerve.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=145\" data-sr-seek=\"145\">2:25<\/a>So I can go back and forth a little bit \u2014 a little bit proximal, a little bit distal \u2014 and I look for where that nerve is at its largest. Then I can pause, and I can get out my measurement tools. So if you were looking at the images, the structure that wasn\u2019t winking in and out of existence is this structure here. So that\u2019s going to be our median nerve.<\/p>\n<\/div>\n<\/section>\n<section class=\"sr-ct-txsec\">\n<h3 class=\"sr-ct-txwin\">Measuring<\/h3>\n<div class=\"sr-ct-txcol\">\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=170\" data-sr-seek=\"170\">2:50<\/a>So I can take our measurement tools, and I can either use an ellipse \u2014 an ellipse will typically work \u2014 or I can use a trace, and I can trace the shape of the nerve. And then I look at the cross-sectional area.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=190\" data-sr-seek=\"190\">3:10<\/a>If you use a threshold of 0.09 centimetres squared, or 9 millimetres squared, that gives you almost 100% sensitivity \u2014 you know, high 90s, 100% sensitivity \u2014 and around high 80s, low 90s specificity. So that will catch \u2014 well, actually, sorry, 100% sensitivity \u2014 that will basically catch all carpal tunnel syndrome. And it was just that quick and easy.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=212\" data-sr-seek=\"212\">3:32<\/a>Now, as I mentioned, the specificity isn\u2019t quite 100%; it\u2019s sort of hovering around 90% in the studies. If you want to improve your confidence \u2014 you know, the larger it is, the more confident you can be in your diagnosis. So if, instead of it just being a little over that 9 millimetres squared threshold, if it\u2019s 11 millimetres squared, 12 millimetres squared, 13 millimetres squared, then you can be more confident in your diagnosis, particularly if it\u2019s over 12 millimetres squared.<\/p>\n<\/div>\n<\/section>\n<section class=\"sr-ct-txsec\">\n<h3 class=\"sr-ct-txwin\">Confirming<\/h3>\n<div class=\"sr-ct-txcol\">\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=246\" data-sr-seek=\"246\">4:06<\/a>Another finding is if you have the patient wiggle their fingers, you should see the nerve sort of wiggle back and forth. Of course, you should be practising on normals \u2014 and if it doesn\u2019t wiggle, that can be another sign, to improve your confidence in your diagnosis. The other thing you can do is you can scan the nerve more proximal, maybe up until about 10 centimetres more proximal, and you can compare that cross-sectional area. Nerves should only get smaller as you go more distal, but if the nerve has increased in size, that increases the likelihood of carpal tunnel syndrome \u2014 in particular, if the increase in size is larger than 40%, so a factor of 1.4.<\/p>\n<\/div>\n<\/section>\n<section class=\"sr-ct-txsec\">\n<h3 class=\"sr-ct-txwin\">Close<\/h3>\n<div class=\"sr-ct-txcol\">\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=289\" data-sr-seek=\"289\">4:49<\/a>But even if you don\u2019t do those extra things, just using that cutoff of 9 millimetres squared, again, has excellent power to rule out that condition, so you can start looking for other conditions. And did you see how quick and easy that was? So get practising, get using your ultrasound, and best of luck helping your patients. Cheers.<\/p>\n<p class=\"sr-ct-txp\"><a class=\"sr-ct-txt\" href=\"#t=313\" data-sr-seek=\"313\">5:13<\/a>[Closing cards, 5:13\u20135:27 \u2014 no speech.]<\/p>\n<\/div>\n<\/section>\n<\/div>\n<\/details>\n<\/section>\n<section id=\"device\" class=\"sr-choice\">\n<p class=\"sr-ct-krow\">Hardware<\/p>\n<h2>Device and settings<\/h2>\n<p>The left column is the published specification. The right column is what the interface actually showed while this scan was being run, and that is the column I would work from if you are reproducing it. The short version: linear side, musculoskeletal preset, 20 mm of depth, two focus carets in the top half of the image, and nothing touched after 1:04. If this exam is one among many, a multi-geometry head covers it without an argument. If nerve and small-parts imaging is almost all of your week, a multi-geometry head is not a good fit: buy a dedicated high-frequency linear probe instead, because the frequency ceiling is the thing you will hit every day.<\/p>\n<div class=\"sr-ct-dev\">\n<div class=\"sr-ct-dev__grid\">\n<div class=\"sr-ct-dev__col\">\n<p class=\"sr-ct-dev__h\">From the published specification<\/p>\n<p class=\"sr-ct-dev__name\">Suresult D3Ultra<\/p>\n<p class=\"sr-ct-dev__price\">Three geometries in one head; the linear one is what this scan uses &mdash; {{SRX_PRICE:28571}}<\/p>\n<ul class=\"sr-ct-spec\">\n<li><b>Linear side<\/b><span>7.5 and 10 MHz, the frequencies that matter here<\/span><\/li>\n<li><b>Linear depth<\/b><span>20, 40, 60 or 100 mm &middot; 40 mm footprint<\/span><\/li>\n<li><b>Grey scale<\/b><span>256 levels &middot; gain adjustable 30 to 105 dB<\/span><\/li>\n<li><b>Aperture<\/b><span>192 elements driven on 64 channels<\/span><\/li>\n<li><b>Also in the head<\/b><span>Convex and phased geometries, 3.2 and 5.0 MHz<\/span><\/li>\n<li><b>Imaging modes<\/b><span>B and M, plus colour, power and pulsed-wave Doppler<\/span><\/li>\n<li><b>Size<\/b><span>263 g &middot; 156 by 65 by 20 mm<\/span><\/li>\n<li><b>Endurance<\/b><span>Around two hours of continuous scanning<\/span><\/li>\n<li><b>Connects to<\/b><span>iOS, Android or Windows over dual-band Wi-Fi<\/span><\/li>\n<\/ul>\n<\/div>\n<div class=\"sr-ct-dev__col\">\n<p class=\"sr-ct-dev__h\">What the interface showed while this scan ran<\/p>\n<ul class=\"sr-ct-spec\">\n<li><b>Header<\/b><span>SX-6CT GRCEKR009 &middot; MSK preset<\/span><\/li>\n<li><b>Geometry<\/b><span>Linear side &mdash; the image is rectangular for the whole recording<\/span><\/li>\n<li><b>Depth<\/b><span>20 mm &middot; scale marked 0 \/ 5 \/ 10 \/ 15 mm<\/span><\/li>\n<li><b>Focus<\/b><span>Two carets, at roughly 4 mm and 9 mm<\/span><\/li>\n<li><b>Frequency<\/b><span>Not displayed &mdash; a 10 MHz ceiling is stated on camera at 0:12<\/span><\/li>\n<li><b>Mode<\/b><span>B-mode throughout &middot; no M-mode, no Doppler<\/span><\/li>\n<li><b>Measurement<\/b><span>Meas &#9656; AREA\/CIRCUM or TRACE &middot; frozen frame reads AREA 0.08 cm&sup2;<\/span><\/li>\n<li><b>Rail<\/b><span>Gain+, Gain&minus;, Depth, Focus, Dyn., Harmonic, Denoise, B Mode<\/span><\/li>\n<li><b>Software<\/b><span>V 3.6.74 &middot; cine buffer 100\/100 on freeze<\/span><\/li>\n<li><b>Operator note<\/b><span>Preset, depth and focus are set at 1:04 and unchanged to the end<\/span><\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"sr-ct-dev__links\"><a href=\"https:\/\/suresultmed.com\/shop\/handheld-ultrasounds\/d3ultra-multipurpose-handheld-ultrasound\/\">D3Ultra specification and price &rarr;<\/a><a href=\"https:\/\/suresultmed.com\/specialty\/handheld-ultrasound-for-musculoskeletal-msk-medicine\/\">Handheld ultrasound for MSK medicine &rarr;<\/a><a href=\"https:\/\/suresultmed.com\/suresult-video-library\/\">Scan Library &rarr;<\/a><\/div>\n<\/div>\n<\/section>\n<section id=\"related\">\n<p class=\"sr-ct-krow\">Same device, other structures<\/p>\n<h2>Related scans<\/h2>\n<div class=\"sr-ct-rels\"><a class=\"sr-ct-rel\" href=\"https:\/\/suresultmed.com\/suresult-video-library\/\"><span class=\"sr-ct-rel__img\"><img decoding=\"async\" src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/carpal-tunnel-related-de-quervain.jpg\" alt=\"First extensor compartment of the wrist on a handheld linear ultrasound, the scan used to look for tenosynovitis at the radial styloid\" width=\"640\" height=\"360\" loading=\"lazy\"><span class=\"sr-ct-rel__len\">4:34<\/span><\/span><span class=\"sr-ct-rel__b\"><span class=\"sr-ct-rel__t\">De Quervain\u2019s tenosynovitis at the radial styloid<\/span><span class=\"sr-ct-rel__d\">The other wrist scan worth knowing, and one of the conditions that sends a patient to a carpal tunnel clinic in the first place: the first extensor compartment, in transverse.<\/span><span class=\"sr-ct-rel__cta\">Watch in the Library &rarr;<\/span><\/span><\/a><a class=\"sr-ct-rel\" href=\"https:\/\/suresultmed.com\/suresult-video-library\/\"><span class=\"sr-ct-rel__img\"><img decoding=\"async\" src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/carpal-tunnel-related-plantar-fascia.jpg\" alt=\"Plantar fascia measured at its calcaneal insertion on a handheld linear ultrasound, thickness caliper on screen\" width=\"640\" height=\"360\" loading=\"lazy\"><span class=\"sr-ct-rel__len\">3:33<\/span><\/span><span class=\"sr-ct-rel__b\"><span class=\"sr-ct-rel__t\">Plantar fascia: measuring at the insertion<\/span><span class=\"sr-ct-rel__d\">The same measurement discipline applied to a different structure \u2014 find the thickest point, freeze, and read one number against a published threshold.<\/span><span class=\"sr-ct-rel__cta\">Watch in the Library &rarr;<\/span><\/span><\/a><a class=\"sr-ct-rel\" href=\"https:\/\/suresultmed.com\/efast-exam-handheld-ultrasound\/\"><span class=\"sr-ct-rel__img\"><img decoding=\"async\" src=\"https:\/\/suresultmed.com\/wp-content\/uploads\/efast-exam-right-upper-quadrant-poster.jpg\" alt=\"Right upper quadrant scan on a handheld ultrasound: liver and right kidney with the hepatorenal recess between them, Abdomen preset at 240 mm depth\" width=\"640\" height=\"360\" loading=\"lazy\"><span class=\"sr-ct-rel__len\">14:09<\/span><\/span><span class=\"sr-ct-rel__b\"><span class=\"sr-ct-rel__t\">eFAST trauma exam on the same handheld probe<\/span><span class=\"sr-ct-rel__d\">The long-form study on the same hardware: five windows, the presets and depths changing five times, and the full transcript.<\/span><span class=\"sr-ct-rel__cta\">Read the walkthrough &rarr;<\/span><\/span><\/a><\/div>\n<p class=\"sr-ct-hublink\">All the clinical clips, filterable by anatomy and probe, are in the <a href=\"https:\/\/suresultmed.com\/suresult-video-library\/\">Scan Library<\/a>.<\/p>\n<\/section>\n<section id=\"faq\">\n<p class=\"sr-ct-krow\">Asked on this search<\/p>\n<h2>Carpal tunnel questions<\/h2>\n<div class=\"sr-faq sr-ct-faq\">\n<details class=\"sr-ct-q\" open>\n<summary>Can carpal tunnel syndrome be diagnosed with ultrasound?<\/summary>\n<p>Yes. The American Association of Neuromuscular and Electrodiagnostic Medicine rates measurement of median nerve cross-sectional area at the wrist as an accurate diagnostic test for carpal tunnel syndrome, at its highest evidence level. Across the four Class I studies behind that guideline, sensitivity ran from 65% to 97% and specificity from 73% to 98% \u2014 a spread wide enough that the scan sits alongside the clinical picture and nerve conduction studies rather than replacing them. What it adds that electrodiagnosis cannot is the anatomy: a ganglion, a tenosynovitis or a bifid nerve is visible in the same ten seconds.<\/p>\n<p><span class=\"sr-ct-cite\">Source: <a href=\"https:\/\/www.aanem.org\/docs\/default-source\/documents\/nmus-for-dx-of-cts_reaffirmed.pdf?sfvrsn=18610687_1\" rel=\"nofollow noopener\" target=\"_blank\">AANEM evidence-based guideline \u2014 neuromuscular ultrasound for carpal tunnel syndrome<\/a>. Accessed September 5, 2026.<\/span><\/details>\n<details class=\"sr-ct-q\">\n<summary>How do you identify the median nerve on ultrasound?<\/summary>\n<p>By tilting. In a transverse view of the anterior wrist the median nerve sits among the flexor tendons and looks much like them \u2014 a speckled, honeycomb oval. Tendons are far more sensitive to anisotropy than nerves, so angling the transducer off-perpendicular makes the tendons darken and drop out of the image while the nerve stays bright. The structure still there at an angle is the nerve. That single manoeuvre, at 1:40 in the walkthrough above, is the whole identification step.<\/p>\n<p><span class=\"sr-ct-cite\">Stated by the presenting clinician in the recording above.<\/span><\/details>\n<details class=\"sr-ct-q\">\n<summary>What is a normal median nerve cross-sectional area?<\/summary>\n<p>A systematic review pooling 41 studies and 2,504 nerves put the mean cross-sectional area at the carpal tunnel inlet at 8.74 mm\u00b2 in healthy people, with a 95% confidence interval of 8.45 to 9.03 mm\u00b2. Diagnostic cut-offs sit right on top of that range: the Class I studies behind the AANEM guideline used 8.5 to 10 mm\u00b2, and a meta-analysis of 28 studies covering 3,995 wrists found 9 mm\u00b2 or more the best single criterion, at 87.3% sensitivity and 83.3% specificity. The frozen frame in the walkthrough reads 0.08 cm\u00b2 \u2014 8 mm\u00b2 \u2014 which is under all of them.<\/p>\n<p><span class=\"sr-ct-cite\">Source: <a href=\"https:\/\/www.nature.com\/articles\/s41598-022-13058-8\" rel=\"nofollow noopener\" target=\"_blank\">Normative reference values of the median nerve cross-sectional area in healthy individuals<\/a>. Accessed September 5, 2026.<\/span><\/details>\n<details class=\"sr-ct-q\">\n<summary>Where in the wrist is the median nerve measured?<\/summary>\n<p>At the carpal tunnel inlet, the level of the pisiform, in a true transverse plane; the outlet at the hook of the hamate is the second measured level. The area is taken where the nerve is widest, which is why the walkthrough sweeps a short distance proximal and distal before freezing rather than measuring the first clean image. Every Class I study behind the AANEM guideline used direct tracing, drawn inside the hyperechoic rim of the nerve \u2014 trace around the rim instead and the number comes back too big.<\/p>\n<p><span class=\"sr-ct-cite\">Source: <a href=\"https:\/\/www.aanem.org\/docs\/default-source\/documents\/nmus-for-dx-of-cts_reaffirmed.pdf?sfvrsn=18610687_1\" rel=\"nofollow noopener\" target=\"_blank\">AANEM evidence-based guideline \u2014 neuromuscular ultrasound for carpal tunnel syndrome<\/a>. Accessed September 5, 2026.<\/span><\/details>\n<details class=\"sr-ct-q\">\n<summary>Does comparing the wrist with the forearm add anything?<\/summary>\n<p>It does, and it is the manoeuvre at 4:06 in the walkthrough. Dividing the nerve\u2019s area at the wrist by its area in the mid-forearm gives the wrist-to-forearm ratio, which is close to 1.0 in asymptomatic volunteers and averaged 2.1 in patients presenting with carpal tunnel syndrome. In that series a ratio of 1.4 detected every affected patient. It is worth the extra ten seconds whenever a single wrist measurement lands close to the cut-off.<\/p>\n<p><span class=\"sr-ct-cite\">Source: <a href=\"https:\/\/europepmc.org\/article\/MED\/18387336\" rel=\"nofollow noopener\" target=\"_blank\">The ultrasonographic wrist-to-forearm median nerve area ratio in carpal tunnel syndrome<\/a>. Accessed September 5, 2026.<\/span><\/details>\n<details class=\"sr-ct-q\">\n<summary>Can a carpal tunnel ultrasound be done on a handheld probe?<\/summary>\n<p>It is done on one in the recording above, and the operator says plainly what he is giving up: the unit tops out at 10 MHz, and 12, 15 or 18 MHz would resolve the fascicles better. Resolution is the whole argument on a nerve scan, so buy the highest linear frequency you will actually use. My own line is this \u2014 a general-purpose head is enough to take a cross-sectional area and make the call, and if nerve and small-parts work is most of your week, a dedicated high-frequency linear probe is the better purchase.<\/p>\n<p><span class=\"sr-ct-cite\">Stated by the presenting clinician in the recording above.<\/span><\/details>\n<\/div>\n<\/section>\n<section id=\"sources\">\n<p class=\"sr-ct-krow\">Provenance<\/p>\n<h2>Sources<\/h2>\n<ul class=\"sr-ct-src\">\n<li><a href=\"https:\/\/www.aanem.org\/docs\/default-source\/documents\/nmus-for-dx-of-cts_reaffirmed.pdf?sfvrsn=18610687_1\" rel=\"nofollow noopener\" target=\"_blank\">AANEM evidence-based guideline \u2014 neuromuscular ultrasound for carpal tunnel syndrome<\/a><span>Cartwright, M. S. et al. Muscle &amp; Nerve, 2012;46(2):287\u2013293; reaffirmed September 2017. Rates median nerve cross-sectional area at the wrist as an accurate diagnostic test (Level A); the Class I cut-offs range from 8.5 to 10 mm\u00b2 and all used direct tracing. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/europepmc.org\/article\/MED\/22542258\" rel=\"nofollow noopener\" target=\"_blank\">Ultrasonography for diagnosing carpal tunnel syndrome: a meta-analysis of diagnostic test accuracy<\/a><span>Tai, T. W. et al. Ultrasound in Medicine &amp; Biology, 2012;38(7). Twenty-eight trials, 3,995 wrists. Source of the 9 mm\u00b2 inlet criterion quoted on this page, at 87.3% sensitivity and 83.3% specificity. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/www.nature.com\/articles\/s41598-022-13058-8\" rel=\"nofollow noopener\" target=\"_blank\">Normative reference values of the median nerve cross-sectional area in healthy individuals<\/a><span>Ng, A. J. T. et al. Scientific Reports, 2022;12:9217. Systematic review of 41 studies and 2,504 nerves. Source of the 8.74 mm\u00b2 pooled mean at the carpal tunnel inlet, CI 8.45\u20139.03, and of the inlet and outlet landmarks. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/europepmc.org\/article\/MED\/18387336\" rel=\"nofollow noopener\" target=\"_blank\">The ultrasonographic wrist-to-forearm median nerve area ratio in carpal tunnel syndrome<\/a><span>Hobson-Webb, L. D. et al. Clinical Neurophysiology, 2008;119(6). Source of the wrist-to-forearm ratio figures: 1.0 \u00b1 0.1 in asymptomatic volunteers, 2.1 \u00b1 0.5 in patients, and 100% sensitivity at a ratio of 1.4. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/europepmc.org\/article\/MED\/22244369\" rel=\"nofollow noopener\" target=\"_blank\">Meta-analysis on the performance of sonography for the diagnosis of carpal tunnel syndrome<\/a><span>Descatha, A. et al. Seminars in Arthritis and Rheumatism, 2012;41(6). Pools sensitivity and specificity threshold band by threshold band, which is where the trade-off across the 8.5\u201313 mm\u00b2 range comes from. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/suresultmed.com\/shop\/handheld-ultrasounds\/d3ultra-multipurpose-handheld-ultrasound\/\" rel=\"nofollow noopener\" target=\"_blank\">Suresult D3Ultra product page<\/a><span>Linear frequency options and their depth settings, aperture and channel counts, grey levels, gain range and weight, taken from the published product attribute table. Accessed September 5, 2026.<\/span><\/li>\n<li><a href=\"https:\/\/www.youtube.com\/watch?v=ryb57wX1dGg\" rel=\"nofollow noopener\" target=\"_blank\">Suresult channel \u2014 the recording on this page<\/a><span>\u201cCarpal Tunnel Syndrome Evaluation with Handheld Ultrasound\u201d, published 13 October 2025. Duration 5:27. The transcript, the key moments and every scan frame on this page are drawn from it. Accessed September 5, 2026.<\/span><\/li>\n<\/ul>\n<\/section>\n<div class=\"sr-final-cta\">\n<div>\n<h2>How much frequency do you actually need for nerve work?<\/h2>\n<p>Ten megahertz is enough to find the median nerve, freeze on its widest point and take the area the diagnosis turns on. Twelve to eighteen shows you the fascicles inside it. Tell us which scans fill your week and you will get a direct answer on where the extra frequency earns its money and where it does not.<\/p>\n<\/div>\n<div class=\"sr-chat-link\">\n<button class=\"sr-crisp-consult-btn\" type=\"button\" data-sr-crisp-open onclick=\"window.$crisp=window.$crisp||[];window.$crisp.push(['do','chat:open']);\">ONLINE EXPERT CONSULT<\/button>\n<\/div>\n<\/div>\n<nav id=\"sr-ct-toc\" class=\"sr-light-toc sr-sticky-toc sr-article-toc\" data-suresult-toc data-sr-hide-on-wide-table aria-label=\"Carpal tunnel walkthrough navigation\">\n<div class=\"sr-light-toc__head\">\n<div class=\"sr-light-toc__title\">On this page<\/div>\n<p><span class=\"sr-light-toc__progress\" id=\"sr-ct-progress\">0%<\/span><\/div>\n<div class=\"sr-light-toc__links\"><a href=\"#quick-answer\">Quick answer<\/a><a href=\"#decision-chain\">The decision chain<\/a><a href=\"#key-moments\">Key moments<\/a><a href=\"#what-it-shows\">What this scan shows<\/a><a href=\"#transcript\">Full transcript<\/a><a href=\"#device\">Device and settings<\/a><a href=\"#related\">Related scans<\/a><a href=\"#faq\">Carpal tunnel questions<\/a><a href=\"#sources\">Sources<\/a><\/div>\n<p class=\"sr-light-toc__note\">Not sure how much linear frequency your nerve work actually needs?<\/p>\n<p><button class=\"sr-crisp-consult-btn\" type=\"button\" data-sr-crisp-open onclick=\"window.$crisp=window.$crisp||[];window.$crisp.push(['do','chat:open']);\">ONLINE EXPERT CONSULT<\/button><br \/>\n<\/nav>\n<\/div>\n<p><script>(function(){\nvar AMP=String.fromCharCode(38);\nvar VID='ryb57wX1dGg';\nfunction embed(start){\nvar u='https:\/\/www.youtube-nocookie.com\/embed\/'+VID+'?rel=0'+AMP+'autoplay=1';\nif(start){u=u+AMP+'start='+start;}\nreturn u;\n}\nfunction mount(start){\nvar pl=document.getElementById('sr-ct-player');\nif(!pl){return null;}\nif(pl.classList.contains('is-live')){\nvar fr=pl.querySelector('iframe');\nif(fr){fr.src=embed(start);}\nreturn pl;\n}\nvar f=document.createElement('iframe');\nf.src=embed(start);\nf.title='Carpal tunnel ultrasound: the median nerve scan, full walkthrough';\nf.allow='accelerometer;autoplay;clipboard-write;encrypted-media;gyroscope;picture-in-picture';\nf.setAttribute('allowfullscreen','');\npl.innerHTML='';\npl.appendChild(f);\npl.classList.add('is-live');\nreturn pl;\n}\nvar p0=document.getElementById('sr-ct-player');\nif(p0){p0.addEventListener('click',function(){mount(0);});}\nvar tx=document.getElementById('sr-ct-transcript');\nif(tx){\nif(window.matchMedia('(max-width:768px)').matches){tx.removeAttribute('open');}\n}\ndocument.addEventListener('click',function(e){\nvar t0=e.target;\nif(!t0){return;}\nif(!t0.closest){return;}\nvar a=t0.closest('[data-sr-seek]');\nif(!a){return;}\ne.preventDefault();\nvar pl=mount(a.getAttribute('data-sr-seek'));\nif(pl){pl.scrollIntoView({behavior:'smooth',block:'start'});}\n});\nvar toc=document.getElementById('sr-ct-toc');\nif(toc){\nvar 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v=m>0?Math.round(h.scrollTop\/m*100):0;\nif(pr){pr.textContent=v+'%';}\n}\nwindow.addEventListener('scroll',function(){\nif(tick){return;}\ntick=true;\nrequestAnimationFrame(upd);\n},{passive:true});\nupd();\n})();<\/script><br \/>\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/#article\",\"headline\":\"Carpal Tunnel Ultrasound: Measuring the Median Nerve in Five Minutes\",\"description\":\"A carpal tunnel ultrasound run end to end on a handheld probe: separating the median nerve from the flexor tendons by anisotropy, sweeping for the largest cross-section, taking the area with the on-device ellipse or trace, and reading it against a published cut-off \u2014 with timestamped key moments, the full transcript, and the preset, depth and focus read off the device 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education\"]}],\"publisher\":{\"@type\":\"Organization\",\"@id\":\"https:\/\/suresultmed.com\/#organization\",\"name\":\"Suresult\",\"url\":\"https:\/\/suresultmed.com\/\"},\"video\":{\"@id\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/#video\"},\"about\":{\"@type\":\"MedicalTest\",\"name\":\"Median nerve ultrasound at the carpal tunnel\"}},{\"@type\":\"VideoObject\",\"@id\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/#video\",\"name\":\"Carpal tunnel ultrasound \u2014 the median nerve scan, full walkthrough\",\"description\":\"A five-minute median nerve scan at the wrist on a handheld probe. Anisotropy used to tell nerve from tendon, a proximal-to-distal sweep for the largest cross-section, the on-device ellipse and trace tools used to take a cross-sectional area, and two confirmatory manoeuvres: finger movement and a wrist-to-forearm comparison.\",\"thumbnailUrl\":[\"https:\/\/suresultmed.com\/wp-content\/uploads\/carpal-tunnel-median-nerve-anisotropy-poster.jpg\"],\"uploadDate\":\"2025-10-13\",\"duration\":\"PT5M27S\",\"embedUrl\":\"https:\/\/www.youtube-nocookie.com\/embed\/ryb57wX1dGg\",\"isFamilyFriendly\":true,\"inLanguage\":\"en\",\"publisher\":{\"@type\":\"Organization\",\"@id\":\"https:\/\/suresultmed.com\/#organization\",\"name\":\"Suresult\",\"url\":\"https:\/\/suresultmed.com\/\"},\"mainEntityOfPage\":{\"@id\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/\"},\"transcript\":\"[Introducing himself and the exam.] Today I\u2019d like to show you how to evaluate for carpal tunnel syndrome \u2014 a compression peripheral neuropathy of the median nerve at the wrist, or at the carpal tunnel. So ideally you\u2019re using as high a frequency probe as you have access to, a linear probe. But today I\u2019m going to actually use a Suresult D3Ultra, which is a dual-purpose probe and it only goes up to 10 megahertz. Now, ideally 12 megahertz is better, 15 megahertz is better, 18 megahertz is better \u2014 but use what you have. And I want to show that you can use a general-purpose probe to diagnose carpal tunnel syndrome. So I\u2019ve already applied gel to the transducer, and I have my patient in my preferred position. I find this position \u2014 if you can pull a table close by, or if you have a table in your office where the patient can just lay their arm down, that\u2019s best. Of course, this is such a quick and simple scan you could just hold their arm and scan, which is what I typically do. It\u2019s so quick and easy. Okay, so I have things set up and we can go. I like to use sort of the presets \u2014 general musculoskeletal preset. Sometimes your unit \u2014 I\u2019m not sure what unit you\u2019re using \u2014 may have a nerve preset, but even a general musculoskeletal preset should work. So, as you can see from what we\u2019re seeing, there\u2019s a heck of a lot going on, right? And of course you want to make sure your focus points are set correctly, the gain is set correctly and depth is set correctly, so you can get as best a picture as you can. So I\u2019m going back and forth here, and you\u2019ll see that there\u2019s so many structures. What the heck are we looking for? Well, as I tilt back and forth, things wink in and out of existence \u2014 this is an imaging artifact called anisotropy, and tendons are more sensitive than nerves. Now in cross-section a nerve and a tendon look very similar, but since nerves are less sensitive to anisotropy, the structure which is more persistent is going to be the nerve. So as I go back and forth, you\u2019ll see that there\u2019s one thing that looks like a tendon, just like the other tendons, but it doesn\u2019t go black as I tilt back and forth. And that\u2019s going to be the nerve. So I can go back and forth a little bit \u2014 a little bit proximal, a little bit distal \u2014 and I look for where that nerve is at its largest. Then I can pause, and I can get out my measurement tools. So if you were looking at the images, the structure that wasn\u2019t winking in and out of existence is this structure here. So that\u2019s going to be our median nerve. So I can take our measurement tools, and I can either use an ellipse \u2014 an ellipse will typically work \u2014 or I can use a trace, and I can trace the shape of the nerve. And then I look at the cross-sectional area. If you use a threshold of 0.09 centimetres squared, or 9 millimetres squared, that gives you almost 100% sensitivity \u2014 you know, high 90s, 100% sensitivity \u2014 and around high 80s, low 90s specificity. So that will catch \u2014 well, actually, sorry, 100% sensitivity \u2014 that will basically catch all carpal tunnel syndrome. And it was just that quick and easy. Now, as I mentioned, the specificity isn\u2019t quite 100%; it\u2019s sort of hovering around 90% in the studies. If you want to improve your confidence \u2014 you know, the larger it is, the more confident you can be in your diagnosis. So if, instead of it just being a little over that 9 millimetres squared threshold, if it\u2019s 11 millimetres squared, 12 millimetres squared, 13 millimetres squared, then you can be more confident in your diagnosis, particularly if it\u2019s over 12 millimetres squared. Another finding is if you have the patient wiggle their fingers, you should see the nerve sort of wiggle back and forth. Of course, you should be practising on normals \u2014 and if it doesn\u2019t wiggle, that can be another sign, to improve your confidence in your diagnosis. The other thing you can do is you can scan the nerve more proximal, maybe up until about 10 centimetres more proximal, and you can compare that cross-sectional area. Nerves should only get smaller as you go more distal, but if the nerve has increased in size, that increases the likelihood of carpal tunnel syndrome \u2014 in particular, if the increase in size is larger than 40%, so a factor of 1.4. But even if you don\u2019t do those extra things, just using that cutoff of 9 millimetres squared, again, has excellent power to rule out that condition, so you can start looking for other conditions. And did you see how quick and easy that was? So get practising, get using your ultrasound, and best of luck helping your patients. Cheers. 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The American Association of Neuromuscular and Electrodiagnostic Medicine rates measurement of median nerve cross-sectional area at the wrist as an accurate diagnostic test for carpal tunnel syndrome, at its highest evidence level. Across the four Class I studies behind that guideline, sensitivity ran from 65% to 97% and specificity from 73% to 98% \u2014 a spread wide enough that the scan sits alongside the clinical picture and nerve conduction studies rather than replacing them. What it adds that electrodiagnosis cannot is the anatomy: a ganglion, a tenosynovitis or a bifid nerve is visible in the same ten seconds.\"}},{\"@type\":\"Question\",\"name\":\"How do you identify the median nerve on ultrasound?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"By tilting. In a transverse view of the anterior wrist the median nerve sits among the flexor tendons and looks much like them \u2014 a speckled, honeycomb oval. Tendons are far more sensitive to anisotropy than nerves, so angling the transducer off-perpendicular makes the tendons darken and drop out of the image while the nerve stays bright. The structure still there at an angle is the nerve. That single manoeuvre, at 1:40 in the walkthrough above, is the whole identification step.\"}},{\"@type\":\"Question\",\"name\":\"What is a normal median nerve cross-sectional area?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"A systematic review pooling 41 studies and 2,504 nerves put the mean cross-sectional area at the carpal tunnel inlet at 8.74 mm\u00b2 in healthy people, with a 95% confidence interval of 8.45 to 9.03 mm\u00b2. Diagnostic cut-offs sit right on top of that range: the Class I studies behind the AANEM guideline used 8.5 to 10 mm\u00b2, and a meta-analysis of 28 studies covering 3,995 wrists found 9 mm\u00b2 or more the best single criterion, at 87.3% sensitivity and 83.3% specificity. The frozen frame in the walkthrough reads 0.08 cm\u00b2 \u2014 8 mm\u00b2 \u2014 which is under all of them.\"}},{\"@type\":\"Question\",\"name\":\"Where in the wrist is the median nerve measured?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"At the carpal tunnel inlet, the level of the pisiform, in a true transverse plane; the outlet at the hook of the hamate is the second measured level. The area is taken where the nerve is widest, which is why the walkthrough sweeps a short distance proximal and distal before freezing rather than measuring the first clean image. Every Class I study behind the AANEM guideline used direct tracing, drawn inside the hyperechoic rim of the nerve \u2014 trace around the rim instead and the number comes back too big.\"}},{\"@type\":\"Question\",\"name\":\"Does comparing the wrist with the forearm add anything?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It does, and it is the manoeuvre at 4:06 in the walkthrough. Dividing the nerve\u2019s area at the wrist by its area in the mid-forearm gives the wrist-to-forearm ratio, which is close to 1.0 in asymptomatic volunteers and averaged 2.1 in patients presenting with carpal tunnel syndrome. In that series a ratio of 1.4 detected every affected patient. It is worth the extra ten seconds whenever a single wrist measurement lands close to the cut-off.\"}},{\"@type\":\"Question\",\"name\":\"Can a carpal tunnel ultrasound be done on a handheld probe?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It is done on one in the recording above, and the operator says plainly what he is giving up: the unit tops out at 10 MHz, and 12, 15 or 18 MHz would resolve the fascicles better. Resolution is the whole argument on a nerve scan, so buy the highest linear frequency you will actually use. My own line is this \u2014 a general-purpose head is enough to take a cross-sectional area and make the call, and if nerve and small-parts work is most of your week, a dedicated high-frequency linear probe is the better purchase.\"}}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/suresultmed.com\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Scan Library\",\"item\":\"https:\/\/suresultmed.com\/suresult-video-library\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"Carpal tunnel ultrasound: measuring the median nerve\",\"item\":\"https:\/\/suresultmed.com\/carpal-tunnel-ultrasound-median-nerve\/\"}]}]}<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>One structure, one number, five minutes. 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