Diagnostic imaging matters


30 25 20 15 10 5 0


A


Diatrizoate Ioxithalamate Ioxaglate Iohexol Iopamidol Ioversol Iopromide Iobitridol Iomeprol Iodixanol


150 180 200 240 250 270 300 320 350 370 380 400 Iodine content of contrast media (mg/ml)


Figure 2: Viscosity of contrast media: (A) room temperature (~20o Developed from data presented in reference 1.


delivery rate is in the range of 8–10 ml/s.8 In small or


narrow arteries, there is no benefit in increasing the rate, as the associated increase in injection pressure may damage the artery or target organ, and there is a risk that excessive contrast medium would flow back into the larger feeding artery and thus be wasted.8


Contrast media viscosity


The viscosity of a contrast medium depends on a range of factors, including the iodine content, molecular weight, chemical structure of the molecule and temperature at which the agent is injected.9


Viscosity increases as the


iodine concentration and molecular weight increase, whereas it decreases as the temperature at which it is injected increases.


The dependence of viscosity on temperature is critical, because differences in viscosity between contrast media at room temperature (20–25ºC) are substantially reduced if the contrast medium is warmed to body temperature (37ºC) (Figure 2). Thus, contrast media that are viscous at room temperature can actually be easier to administer and better tolerated if administered at body temperature.9


Viscosity as a potential factor in CIN Persson et al proposed that viscosity is a key pathogenic factor in the development of CIN;3–5


this hypothesis is


largely based on preclinical models in rats. Recently, Jost et al provided support for the hypothesis based on a study of the impact of viscosity on renal retention of contrast media in pigs.6


The authors concluded that differences


30 25 20 15 10 5 0


B


Diatrizoate Ioxithalamate Ioxaglate Iohexol Iopamidol Ioversol Iopromide Iobitridol Iomeprol Iodixanol


150 180 200 240 250 270 300 320 350 370 380 400 Iodine content of contrast media (mg/ml)


C); (B) body temperature (37o C)1


in viscosity between contrast media may be the cause of variations in renal retention and elimination kinetics. However, their conclusions were not supported by other markers of renal function.


It is important to keep in mind that animal renal physiology (particularly that of rats) is very different from that of humans and that this might be relevant in determining how appropriate interpretations relying on rat data alone might be. The main differences between preclinical animal models and humans include: • Higher physiological urine concentrations in rats10 • Higher concentrations of contrast medium in rat urine than in human urine10


• Up to 10 times higher urinary protein excretion in rats than in humans; proteinuria is close to 0 in healthy humans, and any measurable proteinuria in humans is considered pathological10


• Shorter delayed elimination of contrast media in humans11 than the 180 minutes found by Jost et al in minipigs6


The viscosity hypothesis in humans is supported by a registry study by Liss et al,12


in which iodixanol was


associated with higher CIN rates than ioxaglate. However, the retrospective nature of the data involved and notable baseline differences in the treatment groups (including rates of previous renal failure or dialysis) make these data difficult to interpret.13


Jakobsen et al observed a weak enhancement of the renal cortex that peaked at 24 hours and lasted up to 120 hours,


4


Viscosity (mPa.s)


Viscosity (mPa.s)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12