Longitudinal and Transverse Uniformity in Clinical Whole Body Counting by an Improved Technique

Eine neue Technik, die einen einzelnen Natrium-Jodid-(Tl)-Detektor (9 cm x 6,3 cm) in zwei Positionen verwendet und auf der Ansprechkurve des Detektors beruht wird beschrieben. Ebenso wird ein anderes Verfahren zur Energiewahl angewendet, das sich als zweckmäßig erwiesen hat, um die Zählratenabhängigkeit von der Quellentiefe zu reduzieren. Verschiedene Teile des Compton-Continuums wurden als Grundlage der Messung verwendet anstelle von Tal und Photo-Peak. Für transversale Uniformität wurde gefunden, daß das Energieband, das einer 50% normalisierten Zählrate der Halbtiefe entspricht zu einer flachen Ansprechkurve mit minimalen Variationen führt. Für die longitudinale Uniformität muß die Lagedifferenz der beiden Positionen des Detektors ungefähr gleich der vollen Weite beim Halbmaximum der Ansprechkurve sein. Die Technik des Bezugs zur Ansprechkurve, die beschrieben wird, ist verschieden von der üblicherweise verwendeten Technik der Iso-Ansprechkurven.

Summary

A new technique using a single Nal(Tl) detector (9 cm × 6.3 cm) in two positions and based on the response curves of the detector has been described. Also a different approach to select the energy band was adopted which is helpful in reducing the dependence of counting efficiency on source depth. Various portions of the compton continuum were taken rather than confining to valley and photopeak. For transverse uniformity it was found that the energy band which gave 50% normalized count rate at half depth would give a resultant flat response with least variation. For longitudinal uniformity the separation between the two positions of the detector need to be nearly equal to the full width at half maximum of the response curve. The response curve coupling technique described here is different from the commonly used technique of iso-response curves.

^* Institute of Nuclear Medicine and Allied Sciences, Delhi-7.

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