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Date of last update: 8/13/2017.

Forum Name: Urology Topics

Question: Risk of radiation exposure in diagnostic CT


 megb - Wed Jul 28, 2010 6:36 pm

My daughter just returned from the ER after suffering form excruciating pain on and off, nausea/vomiting for 5 hours...flank pain, groin pain, etc. and was diagnosed with kidney stones. This is the second round of similar pain/symptoms in 3 weeks. The doctors decided that, because of her gender and age, a CT scan was too risky (radiation). She has never had a CT scan before (one extra of a foot when she was 11) and is currently 20 years old. So, they sent her home with advil and a recommendation to drink water and go see her GP. Is the threat of radiation that great to preclude a test for a definitive diagnosis? Is there a better/risk free alternative that will offer similar diagnostic information?
 Dr.M.Aroon kamath - Tue Aug 10, 2010 7:02 am

User avatar Hi,

Non-contrast thin section helical CT is currently regarded as the most useful method to diagnose urinary tract calculi.

Ultrasound (US) has many inherent advantages, which include,
- lack of ionizing radiation,
- universal availability,
- repeatability,
- non-invasive and
- relatively less expensive.

It is useful in the diagnosis of renal and ureteric calculi. Interpretations are highly “operator dependent” thus, it is prone to inter-observer variations. The greatest challenge with regard to US is the identification of ureteral calculi, particularly particularly when they are in the middle third of the ureter. This limitation of US is due to its inability to scan retroperitoneum due to overlying air filled bowel loops, and proximity bony structures.Ultrasound also is known to miss very small stones (2-3mm). Ultrasound is reliable in pediatric urolithiasis as well than in adults due to increased amount of bowel gas and smaller stone sizes. Ultrasound also is inferior to CT in differentiating obstructing from non-obstructing stones.

The advantages of non-contrast helical CT include,
- less operator-dependency,
- its rapid acquisition times,
- lack of need for iodinated contrast or patient preparation,
- its high sensitivity and specificity for renal, ureteric stones and for ureteral obstruction.
The prominent disadvantage is the radiation that is involved.

In one comparative study for example, following a direct comparison of non-contrast helical CT, ultrasound and intravenous urography (IVU) in the detection of ureteral stones, it was found that CT ranked as the most superior of the three modalities with a sensitivity and specificity of 94% and 97% respectively, with an accuracy of 95%, whereas IVP had a sensitivity and specificity of 52% and 94% respectively and an accuracy of only 66%. Ultrasound ranked third among the three modalities and had a sensitivity and specificity of 19% and 97%, and an accuracy of 45%.

Thus, although non-contrast helical CT has advantages, gonadal radiation has remained an inherent risk. Experts believe that further research is needed to optimize CT imaging parameters, while maintaining diagnostic accuracy and minimizing radiation doses.

Your question is if there is any other method of similar accuracy as the non-contrast helical CT. Presently, generally speaking, CT appears to be more sensitive and specific especially for ureteric stones and in identifying ureteric obstruction.

However, the diagnostic accuracy of ultrasonography could be improved upon by addition of Duplex Doppler ultrasonography. It has been shown that by using duplex doppler, renal obstruction can be identified by
- evaluating the intrarenal hemodynamics for
calculation of the “resistive index”, and
- evaluation of the “ureteric jet effect”.

In normal kidneys, a resistive index of 0.62+/-0.03 is considered normal. Resistive index > 0.7 is seen in obstructed kidneys.
A low level jet that is asymmetric to the other ureter is considered as evidence of partial obstruction and absence of a jet is evidence for a complete obstruction.

Best wishes!

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