Which of the following statements about multi-parametric prostate MRI is TRUE?
Answer C
Multiparametric MRI is being used more commonly for the imaging of prostate cancer. This employs various image acquisition formats including diffusion-weighting, dynamic contrast enhancement and MR spectroscopy to provide additional functional information. This increases specificity for the detection of prostatic malignancy. Intravenous gadolinium is used as an enhancing contrast agent. Most prostate cancer occurs in the peripheral zone and can be visualised as low-signal-intensity areas in a background of high-signal intensity produced by normal tissues on T2-weighted MR images. Diffusion weighting shows the extent of random Brownian motion of water molecules within the tissues, thereby providing information on tissue composition and the integrity of membranes. MR Spectroscopy can differentiate between the metabolic levels of tissues. In healthy prostate, there are high levels of citrate and polyamines and decreased levels of choline. This pattern is reversed in prostate cancer. Choline is a marker of cellular proliferation.
Which of the following statements is INCORRECT?
The use of MRI in the evaluation of renal abnormalities is increasing. It is particularly useful for investigating patients with compromised renal function, severe allergy to iodinated contrast, or where radiation exposure is to be avoided, such as in children and pregnant women. The signal intensity of simple renal cysts on MRI mirrors that of water, appearing hypointense on T1-weighted images and hyperintense on T2-weighted images. EAU guidelines endorse level 3 evidence for MRI to assess venous involvement if the extent of vena caval thrombus if poorly defined on CT scanning in T3renal cell carcinoma. The MRI appearances of renal oncocytoma is typically hypointense as compared to normal renal parenchyma on non-enhanced T1-weighted images. They usually exhibit high signal intensity on T2-weighted sequences.
References and Further Reading:
Nikken JJ and Krestin GP. MRI of the kidney—state of the art. European Radiology (2007) 17(11): 2780–2793.
All of the following agents can be used for a dynamic renography study, except:
Answer B
Renograms are static or dynamic renal scintigraphy studies that employ a radiotracer to study various aspects of renal morphology and function by analysing radiotracer uptake, filtration, secretion and excretion in the kidneys. 99mTechnetium-labelled dimercaptosuccinic acid (DMSA) is the agent most commonly used in static renal scintigraphy scans. DMSA is an organosulphur compound that is actively extracted and bound by functioning nephrons; little is filtered. All the other agents listed can be used in dynamic renal scintigraphy studies to provide information on excretion and drainage from the kidney.
Which of the following statements about a 99mTechnetium-labelled dimercaptosuccinic acid (99mTc-DMSA) renogram is correct?
Following an intravenous injection of the radiotracer compound, 99mTechnetium-labelled dimercaptosuccinic acid static (99mTc-DMSA) renogram images are obtained with a gamma camera three to four hours later. 99mTc-DMSA is a protein bound organosulphur compound that is actively extracted and bound by functioning renal tubules and little is filtered. It is avidly taken up by active proximal convoluted cells largely via peri-tubular uptake (approximately two-thirds) and to a lesser extent via glomerular filtration (one-third). It is minimally excreted in the urine by tubular secretion. Approximately one-third of the isotope is renal bound within 1 hour and 50% within 6 hours. The remainder gets sequestered in the liver, spleen and bones.99mTc-MAG-3 renogram scans are equally capable of assessing split renal function but 99mTc-DMSA scans provide excellent additional assessment of renal morphology and evidence of cortical scarring. The total radiation dose from a 99mTc-DMSA renogram has been shown to be 3.3 mSv.
Which of the following statements about bone scans performed to detect metastatic malignancy is correct?
99mTechnecium-labelled methylene diphosphonate (99mTc-MDP) has high skeletal affinity and rapid blood clearance. 400–800 MBq 99mTc-MDP (half-life of six hours) is injected into a peripheral vein. There is maximal bone uptake by two hours after injection, but imaging is delayed to take place at three to four hours post injection. This delay permits unbound tracer to be eliminated by the kidneys. Voiding is performed immediately prior to imaging to enable visualisation of the pelvis. Uptake is determined by local blood flow and the level of osteoblastic activity. False positive results may be seen at sites of healing fractures, Paget’s disease, osteomyelitis or degenerative bone disease. False negative bone scans may be seen in cases of very aggressive tumours inducing little osteoblastic repair. It may also be seen in diffuse metastatic disease where radioisotope accumulation may be sufficiently uniform to produce a false-negative impression (superscans). Clues to the detection of the so-called superscan include skeletal uptake of greater-than-normal intensity, in relation to the background of the soft tissue and the low or absent uptake in the kidneys.
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