Which of the following statements in relation to dual energy X-ray absorptiometry (DEXA) scans is CORRECT?
DEXA stands for dual energy X-ray absorptiometry and is primarily used to study bone mineral density (BMD). A DEXA scan takes approximately 10–20 minutes to perform depending on the body parts being scanned. Two X-ray beams with differing energy levels are passed through specific bones such as the hip or the lower spine. BMD can be determined from the relative absorption of each beam and subtracting soft tissue absorption. A T-score can then be calculated by comparing the X-ray absorption on the study to reference values for a young healthy adult. WHO criteria defines osteoporosis as a BMD that lies 2.5 standard deviations below that of a healthy subject and this merits immediate initiation of corrective treatment. All men due to be commenced on androgen deprivation therapy (ADT) should have a baseline DEXA scan. During long-term ADT, it may be necessary to introduce regular measurements of BMD based on the initial T-score. BMD should be measured every 2 years if the initial T-score is above −1.0, or every year if the T-score is between −1.0 and −2.5, in the absence of associated risk factors. The risk of bony fractures in men receiving ADT for prostate cancer is 19.4% at 5 years and 40% at 15 years. Contra-indications to DEXA scanning include: Pregnancy and recent administration of a contrast agent, e.g., barium into the gastrointestinal tract.
References and Further Reading:
Shahinian VB, Kuo YF, Freeman JL, and Goodwin JS. Risk of fracture after androgen deprivation for prostate cancer. New England Journal of Medicine (2005) 352: 154–164.
Which of the following statements is TRUE?
Non-ionic contrast agents are 5–10 times safer that ionic agents. Ionic contrast agents such as Urografin have high osmolality (≥1200 mOsm/kg) and an allergy rate of 1/500. Non-ionic contrast agents such as Omnipaque have low osmolality (approximately 600 mOsm/kg) and an allergy rate of 1/2500. In patients with an eGFR > 60 mL/min Metformin does not have to be stopped if less than 100 mL of the contrast agent is being administered intravenously. If >100 mL is being administered or the eGFR is below 60 mL/min, Metformin should be withheld for 48 hours. There is a risk of developing nephrogenic systemic fibrosis (NSF) with the use of gadolinium-based contrast agents (GBCA) in patients with renal failure. NSF is a fibrosing disorder of skin and internal organs in patients with renal insufficiency exposed to GBCA during imaging studies (MRI). The onset of NSF symptoms usually occurs within days to months following exposure to GBCA in the vast majority of patients; however, in rare cases, symptoms have appeared years after the last reported exposure. Anaphylactoid hypersensitivity reactions to intravenous contrast agents are a medical emergency and should be managed as per the UK Resuscitation Council guidelines on emergency treatment of anaphylactic reactions. Specific treatment includes intramuscular administration of 0.5 mg (0.5 mL) of 1:1000 adrenaline, to be repeated after five minutes. This should be supplemented with an antihistamine agent such as chlorpheniramine 10 mg IV and hydrocortisone 200 mg IV.
Regarding telescopes as used in cystoscopy, which of the following statements is true?
The components of a cystoscope are the rod-lens telescope, a bridge, an obturator and an outer sheath. Telescopes are available with varying optical angles at their tips to aid different procedures within the urological tract. Telescopes are often colour-coded with bands around their light lead connector:
The Hopkins Rod-Lens telescope consists of long tubes of glass separated by small lenses of air which improves light passage and overall vision. It is fibre optics which use the concept of total internal reflection for the passage of light or images down a fibre. Cystoscopes range between 17 and 25 French in external diameter.
Nakayama DK. How technology shaped modern surgery. The American Surgeon (2018) 84(6): 753–760.
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