Which of the following statements about diagnostic ultrasonography is INCORRECT?
Ultrasound can be used as a diagnostic medical imaging technique that utilises the interaction between sound waves and different tissues. Alternative current is applied to crystals of a piezoceramic plate in a transducer. Expansion and contraction of these crystals produce longitudinal waves, typically at a frequency varying between 2 and 18 MHz. In humans, the audible range of sound wave frequency is between 20 and 20,000 Hz. As the sound waves travel through tissues some are reflected back and are converted from their mechanical form to electrical energy by the transducer to produce an image.
Artefacts occur due to acoustic shadowing, distal enhancement, edging and reverberation.
During a CT for abdominal trauma which of the following statements is INCORRECT?
An emergency CT needs to be discussed with a radiologist, with a responsible doctor involved in the transfer of the patient if stable enough to undergo imaging. Prior to the emergency CT, the patient needs a urinary catheter and an intravenous cannula in place. 150 mL of intravenous iodinated contrast such as Omnipaque should be injected at 3 mL/ second. Patients are scanned in a cranio-caudal direction. The arterial phase is captured at 25 seconds and the venous phase at 60 seconds. EAU recommends a delayed abdominal and pelvic scan at 10–15 minutes to visualise the collecting systems in all patients with suspected renal trauma, with or without a cystogram. Images are generally obtained in 2.5-mm slices.
References and Further Reading:
Standards of practice and guidance for trauma radiology in severely injured patients, Second Edition. London, UK: The Royal College of Radiologists, 2015.
In relation to an emergency on-table IVU, which of the following is INCORRECT?
An emergency on-table IVU will generally only tell you if there is a normally functioning contralateral kidney and is unlikely to provide reliable or adequate detail on the actual injury itself. Two mL/kg of an iodinated contrast agent such as Omnipaque should be administered as a rapid bolus via a large bore cannula, ideally in placed in the antecubital fossa. A single shot KUB X-ray is then obtained at 10 minutes.
Which of the following statements is INCORRECT?
Urolithiasis during pregnancy is uncommon. A multidisciplinary team approach must be adopted to include the urologist, obstetrician, anaesthetist and radiologist. The health of the mother and the development of the foetus are paramount. There is however an absence of prospective studies in this area. Ultrasound is the primary radiological investigation of choice, followed by either an MRI or a limited IVU. Fortunately, conservative supportive management will result in the spontaneous passage of the stone in the majority of pregnant patients. The accepted safe cumulative dose of ionizing radiation to the foetus in pregnancy is five rad (50 mGy), and no single diagnostic study should exceed this maximum. The most sensitive time period for central nervous system teratogenesis is between 10 and 17 weeks of gestation. Non-urgent radiological testing should therefore be avoided during this period. Rare consequences of excessive fetal radiation exposure include a slight increase in the incidence of some childhood cancers, such as leukaemias and, possibly, a very small change in the frequency of genetic mutations. When surgical intervention is necessary insertion of a nephrostomy to relieve the obstruction along with analgesia is an option. Ureteroscopy and holmium laser lithotripsy in pregnancy have been shown to be safe in a number of reports. However, these trials include small numbers and there exists some controversy on the possible detrimental effects of intracorporeal lithotripsy on the foetus’ hearing.
MRI uses the magnetic properties of hydrogen and its interaction with both a large external magnetic field and radio waves to produce highly detailed images of the human body. The nucleus of an atom consists of protons (positive charge) and neutrons (neutral charge). The most common Hydrogen atom isotope in the human body (Protium) has a single proton in its nucleus and no neutrons. The protons are in motion and spin about their axis. When placed in a magnetic field, the protons always align either parallel or anti-parallel to the direction of the magnetic field. When excited by a radio wave they flip direction. Over time, they flip back, emitting a radio signal (MR signal), which is captured by the scanner.
T1 represents longitudinal relaxation time. This indicates the time required for a substance to become magnetised after first being placed in a magnetic field. This involves a transfer of energy. T1-weighted MR images show fat to be bright and water dark. T2 is the transverse relaxation time (decay). It is a measure of how long transverse magnetisation would last in a perfectly uniform external magnetic field. T2-weighted MR images show fluid/water to be bright and fat to be intermediate to dark.
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