Effects of attenuation map accuracy on attenuation-corrected micro-SPECT images

Chao Wu,Freek J Beekman,Hugo A Gratama Van Andel,Peter Laverman,Otto C Boerman

doi:10.1186/2191-219x-3-7

Abstract

BackgroundIn single-photon emission computed tomography (SPECT), attenuation of photon flux in tissue affects quantitative accuracy of reconstructed images. Attenuation maps derived from X-ray computed tomography (CT) can be employed for attenuation correction. The attenuation coefficients as well as registration accuracy between SPECT and CT can be influenced by several factors. Here we investigate how such inaccuracies influence micro-SPECT quantification.MethodsEffects of (1) misalignments between micro-SPECT and micro-CT through shifts and rotation, (2) globally altered attenuation coefficients and (3) combinations of these were evaluated. Tests were performed with a NEMA NU 4–2008 phantom and with rat cadavers containing sources with known activity.ResultsChanges in measured activities within volumes of interest in phantom images ranged from <1.5% (125I) and <0.6% (201Tl, 99mTc and 111In) for 1-mm shifts to <4.5% (125I) and <1.7% (201Tl, 99mTc and 111In) with large misregistration (3 mm). Changes induced by 15° rotation were smaller than those by 3-mm shifts. By significantly altering attenuation coefficients (±10%), activity changes of <5.2% for 125I and <2.7% for 201Tl, 99mTc and 111In were induced. Similar trends were seen in rat studies.ConclusionsWhile getting sufficient accuracy of attenuation maps in clinical imaging is highly challenging, our results indicate that micro-SPECT quantification is quite robust to various imperfections of attenuation maps.

Highlights

In single-photon emission computed tomography (SPECT), attenuation of photon flux in tissue affects quantitative accuracy of reconstructed images
Hwang et al [10] and Vanhove et al [11] showed that by using attenuation maps derived from micro-CT data, cupping artefacts in micro-SPECT images could be eliminated and quantitative errors could be reduced with iterative attenuation correction [12] and window-based scatter correction [13] methods
To only evaluate the impact of inaccuracies in attenuation maps on the SPECT quantification, we considered these original attenuation maps to be accurate, and we used the SPECT images corrected with these maps as reference images

Summary

Introduction

In single-photon emission computed tomography (SPECT), attenuation of photon flux in tissue affects quantitative accuracy of reconstructed images. Small-animal single-photon emission computed tomography (micro-SPECT) plays an increasingly important role in biomedical research [1,2,3,4,5,6,7,8,9]. Attenuation correction, together with correction for effects such as scatter and camera blurring, is essential for obtaining highly quantitative SPECT images. Hwang et al [10] and Vanhove et al [11] showed that by using attenuation maps derived from micro-CT data, cupping artefacts in micro-SPECT images could be eliminated and quantitative errors could be reduced with iterative attenuation correction [12] and window-based scatter correction [13] methods. Studies of e.g. Kennedy et al [20]

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