INTRODUCTION TO ULTRASOUND STUDIES Ultrasonography is the visualisation of body parts with high frequency sound waves. Two dimensional real time ultrasound enables visualisation of organ anatomy and size as well as the movement of major structures such as cardiac valves. It is excellent at discriminating between solid and cystic lesions. Doppler employs the doppler shift of reflected sound by moving objects to assess movement. Doppler is used primarily to assess movement of blood, its direction, the velocity of flow and the presence or absence of flow turbulence. The combination of 2D and Doppler sonography is called duplex sonography. Colour doppler permits a colour map to be formed of the direction and velocity of flow and is particularly useful in echocardiography in determining the severity of valvular lesions, in assessing stenoses in vascular disease, and in assessing the vascularity of organs and tumours. Ultrasonography and nuclear medicine complement each other most effectively giving anatomical and functional information. Ultrasound is highly dependent upon the operator's skill. We believe that in each study it is essential for the ultrasound physician, as well as the ultrasonographer, to image each patient. 1.GENERAL ABDOMINAL ULTRASOUND In abdominal ultrasound the upper abdominal viscera are inspected. To minimise the obscuration by bowel gas and to assess the non-contracted gall bladder, the preparation involves fasting for at least six hours for an adult. The commonest indication is upper abdominal pain. Ultrasound is the modality of choice in detecting gallstones and enables detection of visceral anatomy, inflammation, obstruction and tumours. Where symptoms are strongly suggestive of gall bladder pathology and yet the ultrasound appearance is normal (possibly apart from some tenderness in the gall bladder region with transducer compression,) acalculous cholecystitis remains a definite possibility. Such patients may be assessed with a hepatobiliary scan and cholecystokinin infusion to assess gall bladder function. With the increasing use of ultrasound, incidental benign liver lesions are a common finding. These are most likely haemangiomas. The ultrasound appearance may be difficult but is not entirely specific on one study alone. Such patients are best investigated with a red blood cell liver scan. Where lesions are small (less than 1.5cm) serial ultrasounds demonstrating no change in size are sufficient for diagnosis. Ultrasound is the simplest means of detecting and measuring abdominal aortic aneurysms and is useful for ongoing surveillance. Ultrasound is the simplest means of detecting hydronephrosis and enables ready visualisation of the parenchyma and measurement of renal sizes. It permits the ready differentiation between renal masses and cysts. Doppler applications within the abdomen include assessment of portal hypertension, aortic-iliac arterial disease and in the assessment of renovascular disease. Technetium DTPA scanning is the preferred initial investigation for suspected renal hypertension and is the ideal method to determine whether hydronephrosis is obstructive. 2.FEMALE PELVIC ULTRASOUND Preparation involves filling the urinary bladder by drinking several glasses of fluid an hour before the study. Transabdominal assessment through the urinary bladder is performed initially. Transvaginal sonography using a slender high frequency transducer is used to give greater anatomic detail if necessary. Ultrasound is the method of choice in initially assessing most conditions of the uterus, adnexae and ovaries, with the exception of cervical carcinoma. With ovarian lesions ultrasound enables discrimination between solid tumours and cysts. Simple cysts are usually benign physiological cysts but with larger cysts their resorption should be checked with a subsequent ultrasound. Occasionally, haemorrhage into follicular cyst occurs. Where the clinical history suggests such a diagnosis, these too can be followed with ultrasound to ensure resorption. Other ovarian cysts that are not simple, however, should be treated with caution and require further investigation. Ultrasound readily stages follicular and endometrial cyclical development, information important in IVF programmes. Uterine fibroids are readily identified, measured and localised with ultrasound. 3. 4.MALE PELVIS AND transrectal PROSTATE ULTRASOUND Transabdominal sonography is employed in assessing prostatism. With the patient's bladder full, better outline and prostatic volume are assessed. Bladder masses and calculi are excluded. Immediately following voiding, imaging enables assessment of residual bladder volume as an indicator of bladder neck obstruction. Assessment of prostatic masses requires transrectal ultrasound and biopsy which can only be performed following referral by an Urologist. This enables high resolution visualisation of the prostate especially the peripheral and transitional zones, where the occurrence of carcinoma is greatest. Ultrasound facilitates good visualisation and localisation for fine needle aspiration. The discrimination of carcinoma from chronic prostatitis on the sonographic appearance alone is difficult and biopsies are required. 5.OBSTETRIC ULTRASOUND In the uncomplicated pregnancy the optimal time to assess gestational age and foetal anatomy is 18 weeks. At this stage ultrasound enables detection of many congenital abnormalities and placenta praevia. In the first trimester where vaginal bleeding necessitates the assessment for viability, in most cases, this can be readily decided with ultrasound. In gestations under 6 weeks a small embryonic pole may not be evident within the sac despite the pregnancy ultimately being viable, and progress assessment is occasionally required. In ectopic pregnancy an extrauterine gestational sac and embryo may be identified but are not consistent findings. The absence of an intrauterine sac, the presence of leakage of fluid into the peritoneal cavity, with a persisting elevation of b HCG and a higher clinical index of suspicion are sufficient to warrant surgical exploration. In "at risk" pregnancies such as with diabetes mellitus, hypertension, poor obstetric history etc., studies in the second and third trimesters may be required to check for possible growth retardation and other complications. Umbilical artery doppler samples also give important information regarding foetal well-being. With placental insufficiency the doppler sample waveforms have high resistance flow with reduced or no diastolic flow evident. 6.MUSCULO SKELETAL ULTRASOUND Shoulder ultrasound is very useful in the assessment of painful shoulder. Many diagnoses can be made simply and non-invasively, including rotator cuff tendon inflammation, partial and complete tendon tears, impingement syndromes, bursitis and joint effusions. Other tendons are amenable to ultrasound investigation including the Achilles and hand tendons. Osteomyelitis The diagnosis can be aided by detection of sub-periosteal fluid collection which can be detected sonographically. 7.VASCULAR DUPLEX ULTRASOUND STUDIES Duplex sonography is the combination of 2D imaging in conjunction with pulsed wave Doppler study to assess blood flow within vessels. Colour Doppler is useful in determination of flow direction and maximal jet velocity facilitating pulse wave Doppler analysis. Arterial and venous examinations are usually lengthy in the order of 45-90 minutes, and require differing ultrasound techniques. Therefore arterial and venous systems are not assessed concurrently. 1.Venous Sonography The most common clinical indications are in suspected deep venous thrombosis or superficial thrombophlebitis, for which venous sonography is the test of choice, surpassing contrast venography. The length of the venous system of interest, usually the deep venous system of the lower limbs, is assessed for the presence of thrombus. Normally a vein will compress completely with transducer compression. When thrombus is present, the vein will not compress completely. The extent of the thrombus, particularly centrally, should be determined. On follow-up studies, following therapy, regression can be documented. Preparation Nil except when there is a need for assessment of intra-abdominal thrombus whence the patient should be fasted. Venous Insufficiency assessment is a lengthy procedure and is usually requested by a vascular surgeon in the pre-operative assessment. 2.Extra-Cranial Bilateral Carotid and Vertebral Artery Examination Duplex and colour Doppler are used to identify the presence of plaque and the degree of stenosis in the carotid vessels. The clinical indications include stroke, TIA's, RIND's, retinal artery occlusion, vertigo, asymptomatic carotid bruit, pre and post endarterectomy assessment and for assessment of suspected subclavian steal. 3.Duplex Arterial Assessment of the Lower Limbs The major clinical indications are for assessment of peripheral vascular disease with claudication, rest pain and absent pulses being the most common signs and symptoms. The test is also used following angioplasty and bypass grafts for assessment of patency. This study usually requires two investigations. Part 1. Involves the assessment of the bilateral lower extremities from the common femoral arteries to the dorsalis pedis arteries. Preparation Nil Part 2. Involves the assessment of aorto-iliac arteries. This is performed when the first part is abnormal, usually to assist with the pre-operative planning. Preparation Fast from midnight 4.Renal Arterial Duplex Sonography This is performed in assessment of hypertensive patients and in the assessment of transplant renal allografts. As a screening test for renovascular hypertension the DTPA or MAG 3 renal scans are preferred. Renal artery duplex studies are highly operator dependent and require optimal intra-abdominal views. Intervening bowel gas substantially hampers the study. Preparation Fast from midnight 5.Deep Abdominal Duplex Studies Similar to 19.4. The clinical indications include assessment of portal hypertension, Budd Chiari syndrome, congenital web, abdominal angina, splenic artery assessment. Preparation Fast from midnight ------2 To begin, it's necessary to understand what sound is before one can understand ultrasound. Sound is our experience of the propagation of pressure wave through some physical elastic medium. Usually the medium is air, but a liquid works well too. A vacuum doesn't. There is no sound in space. The pressure waves are generated from some type of mechanical disturbance. Sound is a transfer of power as well. Mechanical energy is being converted to a wave form that radiates energy away from the disturbance. Mechanical vibrations become vibrating pressure waves, transferring energy to the medium and to objects that the wave contacts. Human hearing is limited. If the vibrational frequency is too fast, too high a frequency, we can't hear it. This is ultrasound, vibrations too fast for us to hear. Vibrations Too Fast To Hear. Human hearing can't go beyond about 18,000 vibrations per second, or 18 kHz. There are mammals that can hear well above this. Bats and whales use echolocation that can reach frequencies above 100 kHz. Higher frequencies have a shorter wavelength. A smaller size allows them to reflect from objects more readily and to give greater information about those objects. Extremely high frequencies are difficult to generate and to measure. There is an upper boundary to usable ultrasound, around 10 MHz currently. Higher frequencies are possible. 18 kHz to 10 MHz Generally, the higher frequencies are used for medical imaging, such as investigating a fetus in the mother's womb. The lower frequencies, 1 MHz or less, having longer wavelengths and greater amplitude for a given input energy, produce greater disruption of the medium. Think of fireworks, the whistlers give high pitched sharp sounds, but the boomers aren't just heard, they also move you, giving you a physical thump in the diaphragm. The greater disruption leads to increased motion and, in a liquid, the very interesting phenomenon of cavitation. Cavitation Under the right conditions, irradiation of a liquid with ultrasound leads to the formation and collapse of gas and vapor filled bubbles or cavities in the solution. The collapse of these bubbles can be violent enough to lead to interesting chemical effects.