ARRT Sonography flashcards

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

ALARA principle

As Low As Reasonably Achievable: use the lowest acoustic output and the shortest exposure time that still produce diagnostic information, limiting both patient and operator exposure.

Thermal index

TI estimates the potential temperature rise in tissue from absorbed acoustic energy; a TI of 1 corresponds roughly to a 1 degree C rise and prompts reduced exposure time.

Mechanical index

MI estimates cavitation risk from peak rarefactional pressure divided by the square root of frequency; FDA limits are 1.9 for most exams and 0.23 for ophthalmic imaging.

Endocavitary probe disinfection

Probes that contact mucous membranes, such as transvaginal and transrectal transducers, require high-level disinfection after each use, whereas intact-skin contact requires only low-level disinfection.

Supine hypotensive syndrome

In late pregnancy the gravid uterus compresses the inferior vena cava when supine, reducing venous return; repositioning to left lateral decubitus restores cardiac output and blood pressure.

Trendelenburg position

Head-down body tilt used for vasovagal syncope and to shift mobile fluid or gas cephalad; it is used cautiously in patients with cardiac or respiratory compromise.

Soft tissue propagation speed

The average speed of sound in soft tissue is 1540 m/s, which underlies the range equation: depth in centimeters equals echo time in microseconds multiplied by 0.077.

Axial resolution

Axial resolution equals spatial pulse length divided by two; it improves with higher frequency, fewer cycles per pulse, and damping. It is the best resolution in the image.

Lateral resolution

Lateral resolution depends on beam width at the focal zone; narrower beams from higher frequency and electronic focusing improve it, and it is generally poorer than axial resolution.

Nyquist limit

The Doppler shift must remain below half the pulse repetition frequency or aliasing occurs; raise the PRF, lower frequency, or shift the baseline to correct it.

Tissue attenuation

Attenuation in soft tissue averages about 0.5 dB per centimeter per megahertz, meaning higher frequencies penetrate poorly and deep structures require a lower-frequency transducer.

Time gain compensation

TGC selectively amplifies echoes that return later and deeper to offset attenuation, producing uniform echogenicity from the near field to the far field of the image.

Portal versus hepatic veins

Portal vein walls are echogenic from their fibrous sheath with hepatopetal flow; hepatic vein walls are nearly invisible with pulsatile flow directed toward the inferior vena cava.

Gallbladder wall thickness

Normal gallbladder wall measures 3 mm or less in a fasting patient; thickening with pericholecystic fluid and a positive sonographic Murphy sign suggests acute cholecystitis.

Common bile duct caliber

A normal common bile duct measures up to 6 mm, increasing roughly 1 mm per decade after age 60 and up to 10 mm after cholecystectomy.

Renal length

Normal adult kidney length is 9 to 12 centimeters; the cortex is hypoechoic to liver and spleen, and the central sinus is hyperechoic from fat and collecting structures.

Abdominal aortic aneurysm

An aortic diameter greater than 3 cm defines aneurysm, measured outer wall to outer wall; 5 cm or more, or rapid enlargement, warrants surgical or endovascular referral.

Hydronephrosis

Anechoic fluid splitting the central renal sinus echo complex; mild shows pelvic dilation, moderate adds calyceal blunting, and severe shows cortical thinning with a tortuous collecting system.

Splenomegaly criteria

Spleen length greater than 13 cm or thickness greater than 5 cm indicates splenomegaly; normal splenic parenchyma is homogeneous and slightly more echogenic than the liver.

Gestational sac timing

A transvaginal gestational sac is visible at about 4.5 to 5 weeks, a yolk sac by 5 to 6 weeks, and a fetal pole with cardiac activity by 6 to 6.5 weeks.

Crown-rump length

CRL is the most accurate dating parameter from 7 to 13 weeks, estimating gestational age within about 5 days when measured in mid-sagittal plane with neutral fetal posture.

Nuchal translucency

Measured at 11 to 14 weeks with CRL 45 to 84 mm in a mid-sagittal neutral neck; increased NT (generally above 3 mm) raises aneuploidy and cardiac defect risk.

Biparietal diameter

BPD is measured from outer to inner skull table at the level of the thalami and cavum septi pellucidi; it is most reliable for dating between 14 and 26 weeks.

Abdominal circumference

AC is the best single parameter for assessing fetal growth and nutrition in the third trimester; it is measured at the level of the stomach bubble and portal sinus.

Amniotic fluid index

AFI sums the deepest vertical pocket in each of four quadrants; normal is 5 to 24 cm, oligohydramnios is under 5 cm, and polyhydramnios is over 24 cm.

Placenta previa

Placental tissue covering or lying within 2 cm of the internal cervical os, confirmed by transvaginal scanning; a low-lying placenta may resolve as the uterus enlarges.

Thyroid echogenicity

Normal thyroid is homogeneous and hyperechoic to the strap muscles; a solid hypoechoic nodule that is taller than wide with microcalcifications raises malignancy suspicion.

Simple cyst criteria

Anechoic, thin-walled, smooth-margined structure with posterior acoustic enhancement and no internal vascularity; these features indicate a benign simple cyst needing no aspiration.

Testicular varicocele

Dilated pampiniform plexus veins greater than 2 to 3 mm that enlarge with Valsalva; most occur on the left because the left gonadal vein drains into the renal vein.

Venous compression for DVT

A normal lower-extremity vein fully compresses under transducer pressure; failure to compress with intraluminal echoes and absent phasic flow indicates acute deep vein thrombosis.

Anisotropy artifact

Tendons and nerves appear falsely hypoechoic when the sound beam is not perpendicular to them; maintaining a 90-degree angle of incidence avoids this misleading appearance.

Fibroadenoma appearance

An oval, circumscribed, hypoechoic solid breast mass with width greater than depth and homogeneous echotexture; most common in young women and usually benign.