Objective comparison of lesion detectability in low and medium-energy collimator iodine-123 mIBG images using a channelized Hotelling observer

Rebecca A Gregory,Jonathan Gear,Glenn Flux,Sue Chua,Wendy A Waddington,Matthew D Aldridge,Lucy Fowkes,Daniel Levine,Iain Murray

doi:10.1088/1361-6560/62/1/17

Abstract

Iodine-123 mIBG imaging is widely regarded as a gold standard for diagnostic studies of neuroblastoma and adult neuroendocrine cancer although the optimal collimator for tumour imaging remains undetermined. Low-energy (LE) high-resolution (HR) collimators provide superior spatial resolution. However due to septal penetration of high-energy photons these provide poorer contrast than medium-energy (ME) general-purpose (GP) collimators. LEGP collimators improve count sensitivity. The aim of this study was to objectively compare the lesion detection efficiency of each collimator to determine the optimal collimator for diagnostic imaging.The septal penetration and sensitivity of each collimator was assessed. Planar images of the patient abdomen were simulated with static scans of a Liqui-Phil™ anthropomorphic phantom with lesion-shaped inserts, acquired with LE and ME collimators on 3 different manufacturers’ gamma camera systems (Skylight (Philips), Intevo (Siemens) and Discovery (GE)). Two-hundred normal and 200 single-lesion abnormal images were created for each collimator. A channelized Hotelling observer (CHO) was developed and validated to score the images for the likelihood of an abnormality. The areas under receiver-operator characteristic (ROC) curves, Az, created from the scores were used to quantify lesion detectability. The CHO ROC curves for the LEHR collimators were inferior to the GP curves for all cameras. The LEHR collimators resulted in statistically significantly smaller Azs (p < 0.05), of on average 0.891 ± 0.004, than for the MEGP collimators, 0.933 ± 0.004. In conclusion, the reduced background provided by MEGP collimators improved 123I mIBG image lesion detectability over LEHR collimators that provided better spatial resolution.

Highlights

Radionuclide imaging with Metaiodobenzylguanidine has a fundamental role in the diagnosis, staging and evaluation of treatment response in childhood neuroblastoma and adult neuroendocrine tumours (NETs) (Gelfand 1993, Shapiro et al 2001, Brisse et al 2011)
Scintigraphy is routinely undertaken using 123I-mIBG in preference to 131I-mIBG, because better quality images can be obtained from 159 keV 123I gamma photons and twenty times more 123I activity can be administered for diagnostic scans (Shapiro et al 1987, Matthay et al 2010)
Iodine-123 is advocated for treatment planning prior to 131I mIBG therapy (Monsieurs et al 2002), despite the fact that the images obtained have been shown to be less sensitive in detecting lesions than post-therapy 131I-mIBG scans (Yang et al 2012)

Summary

Introduction

Radionuclide imaging with Metaiodobenzylguanidine (mIBG) has a fundamental role in the diagnosis, staging and evaluation of treatment response in childhood neuroblastoma and adult neuroendocrine tumours (NETs) (Gelfand 1993, Shapiro et al 2001, Brisse et al 2011). 123I predominantly emits gamma photons at 159 keV (83% abundance), photons above 500 keV (2.3% abundance) are emitted These high energy photons penetrate the septa of low-energy (LE) collimators and down-scatter into the main photo peak energy window, producing background counts that reduce image contrast (Dobbeleir et al 1999). It was demonstrated almost 40 years ago that medium-energy general purpose (MEGP) collimators provide better signal detection than the a LE high-resolution (HR) collimators (Bolmsjo et al 1977).

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