1979, British Journal of Radiology, 52,1 56
Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents) introduction into the patient of radiopaque substances of high atomic number. These substances when irradiated produce hard scatter radiation which can obliterate complete sets of CT-scans, making them unreadable on account of artefacts.
Place of new contrast media in renal failure THE EDITOR—SIR,
It was with great interest that I read "The effect of osmotic diuresis on urinary iodine concentration" (Webb et al., 1978) in your February issue. I believe some observations from our recent experiments and calculations may be of interest and cast some additional light on the place of contrast media of reduced osmolality in advanced renal failure. In patients with normal renal function the urinary tract increases in volume during osmotic diuresis (Dorph et al., 1977) and therefore both the increase in urine flow and the iodine concentration will be of importance for the absorption of X-ray in the urinary tract. Calculations (Golman 1977) have shown that the urinary iodine concentration is the most important parameter. In renal failure the urinary tract may be chronically fully distended by the obligatory (urea) diuresis and the contrast media may be unable to produce any further increase in the diameter of the tubulus (the depth of the X-ray absorbing layer). The urinary iodine concentration thus becomes the only parameter of importance and the significant increase in iodine concentrations obtained using metrizamide instead of the ionic media during the important first 20 min after injection in the study of Webb and colleagues (during both moderate and large mannitol diuresis) could give the increase in X-ray absorption which was just necessary to obtain a diagnostically usable examination. Moreover, the reduced toxicity and pharmacological sideeffects of metrizamide compared to the common ionic media (see Acta Radiologica Supple. 335, various authors 1973; Kolbenstvedt et al., 1979) should be especially important in the presence of renal failure, as the patients may already be out of fluid balance. In children with renal failure where the doses tend to be high per kg body weight the dehydration produced by the ionic media may produce a life-threatening condition and thus the place of contrast media of reduced osmolality must be seriously considered. Yours, etc., K. GOLMAN.
Experimental Department, Malmo Allmanna Sjukhus, S-214 01 Malmo, Sweden. REFERENCES DORPH, S., SOVAK, M., TALNER, L. B., and L. ROSEN, 1977.
Why does kidney size change during i.v. urography? Investigative Radiology, 12, 246. GOLMAN, K., 1977. Physiological consideration on the excretion of contrast media. Journal Beige de Radiologie, 60, 229. KOLBENSTVEDT, A., ANDREW, E., CHRISTOPHERSEN, B., GOLMAN, K., KVARSTEIN, B., and LIEN, H. H., 1979.
Metrizamide (Amipaque) in high-dose urography. Acta Radiologica (in press).
Artefacts in CT scanning THE EDITOR—SIR,
CT-scanning is penetrating diagnostic medical practice at an amazing pace with a wide spectrum of application. Various factors of a technical nature can interfere with the diagnostic quality of the CT-scans, and among them are the
B FIG.
1. (A) A coronal section of the head of a patient with intracerebral calcification as seen before dental treatment. (B) The disastrous effect of dental fillings on control CTscans four weeks later
156
Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents) introduction into the patient of radiopaque substances of high atomic number. These substances when irradiated produce hard scatter radiation which can obliterate complete sets of CT-scans, making them unreadable on account of artefacts.
Place of new contrast media in renal failure THE EDITOR—SIR,
It was with great interest that I read "The effect of osmotic diuresis on urinary iodine concentration" (Webb et al., 1978) in your February issue. I believe some observations from our recent experiments and calculations may be of interest and cast some additional light on the place of contrast media of reduced osmolality in advanced renal failure. In patients with normal renal function the urinary tract increases in volume during osmotic diuresis (Dorph et al., 1977) and therefore both the increase in urine flow and the iodine concentration will be of importance for the absorption of X-ray in the urinary tract. Calculations (Golman 1977) have shown that the urinary iodine concentration is the most important parameter. In renal failure the urinary tract may be chronically fully distended by the obligatory (urea) diuresis and the contrast media may be unable to produce any further increase in the diameter of the tubulus (the depth of the X-ray absorbing layer). The urinary iodine concentration thus becomes the only parameter of importance and the significant increase in iodine concentrations obtained using metrizamide instead of the ionic media during the important first 20 min after injection in the study of Webb and colleagues (during both moderate and large mannitol diuresis) could give the increase in X-ray absorption which was just necessary to obtain a diagnostically usable examination. Moreover, the reduced toxicity and pharmacological sideeffects of metrizamide compared to the common ionic media (see Acta Radiologica Supple. 335, various authors 1973; Kolbenstvedt et al., 1979) should be especially important in the presence of renal failure, as the patients may already be out of fluid balance. In children with renal failure where the doses tend to be high per kg body weight the dehydration produced by the ionic media may produce a life-threatening condition and thus the place of contrast media of reduced osmolality must be seriously considered. Yours, etc., K. GOLMAN.
Experimental Department, Malmo Allmanna Sjukhus, S-214 01 Malmo, Sweden. REFERENCES DORPH, S., SOVAK, M., TALNER, L. B., and L. ROSEN, 1977.
Why does kidney size change during i.v. urography? Investigative Radiology, 12, 246. GOLMAN, K., 1977. Physiological consideration on the excretion of contrast media. Journal Beige de Radiologie, 60, 229. KOLBENSTVEDT, A., ANDREW, E., CHRISTOPHERSEN, B., GOLMAN, K., KVARSTEIN, B., and LIEN, H. H., 1979.
Metrizamide (Amipaque) in high-dose urography. Acta Radiologica (in press).
Artefacts in CT scanning THE EDITOR—SIR,
CT-scanning is penetrating diagnostic medical practice at an amazing pace with a wide spectrum of application. Various factors of a technical nature can interfere with the diagnostic quality of the CT-scans, and among them are the
B FIG.
1. (A) A coronal section of the head of a patient with intracerebral calcification as seen before dental treatment. (B) The disastrous effect of dental fillings on control CTscans four weeks later
156
