ULTRASOUND SCANNING

Introduction to Ultrasound

Ultrasound Scanning Physics Characterized by sound waves of high frequency Higher than the range of human hearing Sound waves are measured in Hertz (Hz) Diagnostic U/S = 1-20 MHz Sound waves are produced by a transducer

Instrumentation - Ultrasound Probes C

Transducers/Probes Sector scanner Linear scanner Curvi-linear scanner Fan-shaped beam Small surface required for contact Cardiac imaging Linear scanner Rectanglular beam Large contact area required Curvi-linear scanner Smaller scan head Wider field of view

Indications As a compliment to abdominal radiographs To determine the origin of an abdominal mass Spleen, Liver To facilitate fine needle aspiration/cystocentesis To evaluate organ parenchyma To rule in/out intestinal obstruction (foreign body) ***If clinical signs or history indicate abdominal ultrasound, then it should be performed even if radiographs are normal!!!

Indications for USG Indications: abdomen, OBG,& Gynec. Abdomen: Liver- Size, configuration, texture and contour. To R/o ascites, abscess, cystic disease etc. Growth – Primary and secondaries. Jaundice: Viral Obstructive – Calculi, growth and annular pancreas.

Renal US Kidney: size and trauma. Congenital: Agenesis Calculi (Radiolucent) Hydronephrosis. Infections and abscess. Tumors

Pancreas Pancreas: Infections – calcification, duct dilatation Complications of pancreatitis. Pseudo cyst and abscess. Spleen: Splenomegaly- Fever and abscess. Portal hypertension RTA – Splenic injury

Abdominal US Abdominal mass, Lymphadenopathy G.I tract: Mass Obstruction Volvulus Worms Omental secondaries

OBG OBG: Missed abortion Ectopic pregnancy 5th week – Gestation sac 6th week - Fetal pole Cardiac activity 12th week – Head (BPD) 18-20 week- Fetal anomaly scan. Placenta: Praevia and abruption. Hydramnios, twins, molar pregnancy. Position of fetus - Cephalic, breech. Gestational age: BPD, HC, AC and FL

Gynec Gynec: Uterus – Size, congenital anomaly (Bifid, septate etc) Mass – Fibroids and growth. Infertility. Ovaries: Ovulation, mass – cysts and growth. P.I.D: Free fluid in POD.

Why do you need both X-ray and USG? Examples Prostatic adenocarcinoma seen on ultrasound Has it spread to the lumbar vertebrae? Coughing patient with mitral regurgitation on echocardiogram Does the patient have pulmonary edema? Enlarged liver on radiographs Can get a guided FNA with ultrasound

Mirror Image Artifact

Comet Tails

Artifacts Acoustic shadowing Acoustic enhancement U/S beam does not pass through an object because of reflection or absorption Black area beyond the surface of the reflector Examples: cystic calculi, bones Acoustic enhancement Hyperintense (bright) regions below objects of low U/S beam attenuation AKA Through transmission Examples: cyst or urinary bladder

Acoustic Shadowing

Acoustic Enhancement

Artifacts Refraction: Occurs when the sound wave reaches two tissues of differing acoustic impedances U/S beam reaching the second tissue changes direction May cause an organ to be improperly displayed

Ultrasound-Guided FNA/ Biopsies Routinely aspirate: Liver (masses and diffuse disease) Spleen (nodules and diffuse disease) Gastrointestinal masses Enlarged lymph nodes Enlarged prostate Pulmonary/ mediastinal masses (usually don’t biopsy due to risk of pneumothorax Occasionally aspirate: Kidneys (esp. if enlarged) Pancreas Urinary bladder masses Never aspirate: Adrenal glands Gall bladder

Ultrasound-Guided FNA/Biopsies Non-aspiration Technique 22g 1.5in needle 10 cc syringe Short jabs into organ Spray onto slide, smear, and check abdomen for hemorrhage

DOPPLER

Waves from stationary and moving sources

Doppler Effect Shift in perceived frequency when either source or listener are moving relative to one another Familiar occurrence in audible sounds Also occurs in medical ultrasound

Please note: the ‘squishing’ of the wave-fronts in the middle diagram and the stretching in the lower diagram are exaggerated. Realistically the Doppler shifts are so small in ultrasound you would hardly see any difference in the wave-fronts compared to the unshifted one on top. These are artists’ diagrams.

Doppler shift Doppler shift is the difference between the transmitted and received frequencies. Transmitted and received frequencies are in the MHz range Doppler shift frequencies often in audible range

Scattering from blood Source of signals for flow imaging: Red blood cells Much smaller than l Rayleigh scatterers Scattering increases with frequency Scattering increases with number of targets Double the number of scatterers, scattered intensity doubles!

Cosine Function h cos q = a/h q a cos 2o = 0.999 a h a cos 60o = 0.5 h

The frequency of the Doppler shift is proportional to the cosine of the Doppler angle Angle formed by the ultrasound beam and the direction of flow Doppler frequency varies with the cosine of the angle. Cosine = 1 for 0o Cosine = ½ for 60o Cosine = 0 for 90o For angles between 0 and 10o, cosine is close to 1. The larger the angle (up to 90o), the smaller the cosine

Angle Correct Error

Range (depth) selection done by a procedure called “gating” Gating +beam dimensions, define “sample volume”

Duplex Mode (Duplex Doppler) B-mode imaging + Doppler

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