Measurement of Renal Parenchymal Transit Time of ^99mTc-MAG₃ Using Factor Analysis

Renal parenchymal transit time of the recently introduced radiopharmaceutical ^99mTc-MAG₃ (mercaptoacetylglycylglylcylglycinel) was measured in 37 kidneys, using factor analysis to separate parenchymal activity from that in the collecting system. A new factor algorithm was employed, based on prior interpolative background subtraction and use of the fact that the initial slope of the collecting system factor time-activity curve must be zero. The only operator intervention required was selection of a rectangular region enclosing the kidney (by identifying two points at opposite corners). Transit time was calculated from the factor time-activity curves both by deconvolution of the parenchymal factor curve and also by measuring the appearance time for collecting system activity from the collecting system factor curve. There was substantial agreement between the two methods. Factor analysis led to a narrower range of normal values than a conventional cortical region-of-interest method, presumably by decreasing crosstalk from the collecting system. In preliminary trials, the parenchymal transit time did not well separate four obstructed from seventeen unobstructed kidneys, but it successfully (p <0.05) separated six transplanted kidneys with acute rejection or acute tubular necrosis from 10 normal transplants.

Zusammenfassung

Bei 37 Nieren wurde die renale Durchflußzeit des neuen Radiopharmazeutikums ^99mTc-MAG₃ unter Benutzung der Faktorenanalyse gemessen. Der Algorithmus erlaubt getrennte Messung von Parenchymaktivität und Aktivität im Sammelrohrsystem. Er basiert auf interpolativer Hintergrundsubtraktion und der Tatsache, daß die Initialsteigung der Zeitaktivitätskurve des Sammelrohrfaktors Null sein muß. Der einzige nicht computergesteuerte Eingriff bestand in der Auswahl eines die Niere umgebenden Rechtecks (definiert durch zwei ge genüberliegende Eckpunkte). Die Durchflußzeit wurde von den Faktorenkurven sowohl durch Dekonvolution des Parenchymfaktors als auch durch die Messung der Erscheinungszeit im Sammelrohrsystem berechnet. Beide Methoden ergaben ähnliche Resultate. Die Faktorenanalyse ergab einen kleineren Normwertbereich als die konventionelle Definition einer Region über der Nierenrinde, wahrscheinlich aufgrund geringeren “crosstalks” vom Sammelrohrsystem. In vorläufigen Versuchen waren Nierenobstruktion (n = 4) und Nichtobstruktion (n = 17) nicht klar unterscheidbar, während akute Tubulusnekrose oder akute Abstoßung transplantierter Nieren (n = 6) von erfolgreich transplantierten Nieren (n = 10) klar unterschieden werden konnten (p <0,05).

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