NAMU CMU flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Axial resolution

The minimum separation of two reflectors along the beam path that can be distinguished. It equals spatial pulse length divided by two and improves with higher frequency and fewer cycles per pulse.

Doppler angle correction

The angle between the ultrasound beam and blood flow. The Doppler shift is proportional to the cosine of this angle; angles near 90 degrees produce no detectable shift, and errors grow as the angle exceeds 60 degrees.

Nyquist limit

Half the pulse repetition frequency. When the Doppler shift exceeds this value, aliasing occurs and the spectral display wraps, showing flow in the opposite direction; raising the PRF or lowering frequency corrects it.

Mechanical index

A measure of cavitation risk related to peak negative pressure divided by the square root of frequency. Higher values increase the chance of bubble collapse, so it is kept low when scanning lung or bowel.

Common bile duct measurement

Measured from inner wall to inner wall in the porta hepatis. Normal is up to 6 mm, increasing about 1 mm per decade after age 60, with up to 10 mm accepted after cholecystectomy.

Sonographic Murphy sign

Focal maximal tenderness elicited when the transducer presses directly over the gallbladder during scanning. It supports acute cholecystitis, especially when combined with wall thickening and pericholecystic fluid.

Hydronephrosis grading

Mild shows anechoic separation of the renal pelvis; moderate adds calyceal blunting; severe shows cortical thinning and a dilated pelvis. It reflects obstruction and is assessed with the bladder and ureter.

Portal hypertension signs

Findings include splenomegaly, ascites, a dilated portal vein over 13 mm, recanalized paraumbilical veins, and reversal of portal flow. These support the diagnosis of portal hypertension in chronic liver disease.

Crown-rump length dating

The most accurate first-trimester dating parameter, measured from 7 to 13 weeks. Gestational age in days approximates CRL in millimeters plus 42 for CRL between 5 and 65 mm.

Nuchal translucency

Anechoic space behind the fetal neck measured at 11 to 13 weeks 6 days with CRL 45 to 84 mm. Increased thickness raises risk of aneuploidy and congenital heart defects.

Amniotic fluid index

Sum of the deepest vertical pockets in four quadrants. Normal is 5 to 24 cm; below 5 cm is oligohydramnios and above 24 cm is polyhydramnios, prompting fetal evaluation.

Endometrial thickness

Measured in the sagittal plane at the thickest point. Up to 4 mm supports atrophy; greater than 4 mm in a postmenopausal woman with bleeding warrants tissue sampling.

ICA versus ECA waveform

The internal carotid shows low-resistance flow with continuous diastole and no early branches. The external carotid shows high resistance, a sharp upstroke, and branches such as the superior thyroid artery.

DVT compression criterion

A vein is considered thrombosed when it fails to collapse completely under graded transducer pressure. Acute thrombus is typically hypoechoic and distends the vein, with reduced phasic flow.

Ankle-brachial index

The ratio of ankle to brachial systolic pressure. Values of 0.9 or less indicate peripheral arterial disease, 0.4 or less suggest critical ischemia, and above 1.4 suggest noncompressible calcified vessels.

Pseudoaneurysm Doppler

A contained arterial leak showing a yin-yang color pattern and a neck with to-and-fro spectral flow. It often follows catheterization and may be treated with compression or thrombin injection.

Ejection fraction

Calculated as end-diastolic volume minus end-systolic volume, divided by end-diastolic volume. Normal is at least 52 percent in men and 54 percent in women by biplane Simpson method.

E over e-prime ratio

The ratio of early mitral inflow velocity to early tissue Doppler velocity. A value above 14 suggests elevated left ventricular filling pressures, while lower values generally indicate normal pressures.

Aortic stenosis severity

Severe stenosis is defined by peak velocity above 4 m/s, mean gradient above 40 mmHg, or valve area below 1.0 square centimeter. Low-flow states may require dobutamine stress for confirmation.

Cardiac tamponade signs

Right atrial systolic collapse, right ventricular diastolic collapse, and a dilated inferior vena cava with reduced respiratory variation. These findings suggest hemodynamically significant pericardial effusion requiring urgent drainage.

TIRADS nodule features

Suspicious thyroid features include solid hypoechoic composition, irregular margins, microcalcifications, and taller-than-wide shape. Spongiform or purely cystic nodules are almost always benign and need no biopsy.

BI-RADS category 3

A probably benign breast finding with a malignancy risk of 2 percent or less. Short-interval follow-up imaging is recommended rather than immediate biopsy, to avoid unnecessary procedures.

Normal lymph node features

A benign node is reniform with a thin hypoechoic cortex, an echogenic fatty hilum, and hilar vascularity. Rounded shape, loss of the hilum, and peripheral flow raise suspicion.

Testicular torsion

Twisting of the spermatic cord causing absent or reduced intratesticular flow and a high-resistance arterial waveform. It is a surgical emergency; the bell-clapper deformity is a predisposing anatomic variant.

Anisotropy artifact

Artifactual hypoechogenicity that occurs when a tendon is not perpendicular to the beam. It can mimic tendinopathy, so the transducer is tilted to restore the normal hyperechoic fibrillar appearance.

Rotator cuff tear

A full-thickness tear shows a focal gap with retracted tendon ends and fluid or bursal herniation. Dynamic imaging with passive arm motion improves detection of partial and full-thickness tears.

Double-contour sign

A hyperechoic line parallel to the hyaline cartilage surface seen in gout. It represents monosodium urate crystal deposition and helps distinguish gout from other arthropathies.

Lung sliding assessment

Normal lung shows shimmering sliding between the visceral and parietal pleura. Absence of sliding with a lung point indicates pneumothorax, while absent sliding without a lung point may reflect other causes.

FAST examination

A focused assessment with sonography for trauma, evaluating pericardial, perihepatic, perisplenic, and pelvic windows. Free fluid appears anechoic and collects in dependent spaces, guiding trauma triage.

Thermal index

An estimate of the temperature rise from absorbed ultrasound energy. It is kept below 1.0 in obstetric scanning and below 2.0 for general adult imaging under the ALARA principle.

ALARA principle

As low as reasonably achievable: use the minimum output and scan time needed for diagnosis. Operators monitor mechanical and thermal indices and adjust settings to reduce patient exposure.

Scope of practice

Sonographers perform examinations and document findings, while physicians interpret results and render diagnoses. Performing studies outside one's training and credentialing raises ethical and legal concerns.