International Scientific Committee of Radionuclides in Nephrourology (ISCORN) Consensus on Renal Transit Time Measurements

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This report is the conclusion of the international consensus committee on renal transit time (subcommittee of the International Scientific Committee of Radionuclides in Nephrourology) and provides recommendations on measurement, normal values, and analysis of clinical utility. Transit time is the time that a tracer remains within the kidney or within a part of the kidney (eg, parenchymal transit time). It can be obtained from a dynamic renogram and a vascular input acquired in standardized conditions by a deconvolution process. Alternatively to transit time measurement, simpler indices were proposed, such as time of maximum, normalized residual activity or renal output efficiency. Transit time has been mainly used in urinary obstruction, renal artery stenosis, or renovascular hypertension and renal transplant. Despite a large amount of published data on obstruction, only the value of normal transit is established. The value of delayed transit remains controversial, probably due to lack of a gold standard for obstruction. Transit time measurements are useful to diagnose renovascular hypertension, as are some of the simpler indices. The committee recommends further collaborative trials.

Section snippets

Methodology

A first draft was discussed by the committee by e-mail. Then, an outline was proposed by Dr. Durand and approved by the other committee members. The whole text was then rewritten based on this outline by Dr. Durand and Dr. Blaufox, including the comments and new references that were proposed and classifying the level of evidence of the references. This version was then submitted to the committee for comments and changes. It is reminded here that a consensus does not mean that all the authors

Basic Facts on Renal TT

In 1956, Taplin and coworkers published the use of 131I-diodrast injected intravenously to produce dynamic acquisitions of kidneys, thus obtaining a time-activity curve.1 These time-activity curves can be used to derive relative renal function,2 but they also provide information on transit, that is, time during which the tracer stays in a given part of kidney. A quantitative analysis of the renogram suggesting the use of deconvolution was proposed as early as 1964.3 Very early, it was suggested

Assessment of Transit

The general technique to assess renal transit in nuclear medicine is to acquire a dynamic scan after a bolus injection. After acquisition, either a qualitative assessment of transit can be done or a quantitative one, which may be either a transit time determination or assessment of a simpler index of transit. (Here, “simple” indices should be understood as “easy to determine.” They may however reflect less simple physiologic parameters.)

Summary

To assess renal transit, two kinds of methods exist. The first one is a measurement of transit time by deconvolution, which was mostly applied to parenchymal transit with DTPA (MAG3 was not introduced until 1986). This measurement provides a parameter that is physiologically relevant (namely, the duration that a molecule stays in the nephron, which is the ratio of the nephron volume to the urine flow). However, a British audit showed a poor intercenter reproducibility of the data processing.81

Application of MTT in Clinical Situations

Renal transit was mostly studied in 3 clinical situations: hydronephrosis, renovascular hypertension (RVHT), and kidney transplantation.

Conclusion

Purest transit parameters (measured transit times) can be obtained by deconvolution but they lack intercenter reproducibility. Simple parameters are more influenced by the input function and do not reflect truly physiological parameters. Moreover, transit is affected by many parameters (hydration state, arterial pressure, reservoir effect, full bladder, posture, etc) More standardization is therefore desirable for both classes of methods. In obstruction, no consensus was reached among the

Appendix

Available online at http://www.ISCORN.org.

Note on References

Only peer-reviewed papers were considered for clinical evidence, not editorials, letters, abstracts, books, or personal communications. Other papers have be taken as useful for their ideas but not for clinical or experimental evidence. The quoted references were classified along the following categories210, 211 (we must however remark that this classification was designed for therapeutic studies, not for diagnostic studies as here). Additional categories were used to adapt the original

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    Note: Throughout the text, the symbol “±” stands for standard deviation.

    Conflicts of interest: K.E.B. was a consultant to Nuclear Diagnostics Ltd (Hermes work stations) from October 2004 to October 2005; he is no longer involved with this company.

    The publication of this paper was made possible by a grant from ISCORN (A. Prigent) and contributions from A.T. Taylor and M.D. Blaufox.

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