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Open Access Original research

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

Chao Wu12*, Hugo A Gratama van Andel23, Peter Laverman4, Otto C Boerman4 and Freek J Beekman13

Author Affiliations

1 Section Radiation, Detection & Medical Imaging, Delft University of Technology, Mekelweg 15, Delft, 2629 JB, the Netherlands

2 Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, STR 5.101, Univeriteitsweg 100, Utrecht, 3584 CG, the Netherlands

3 MILabs B.V., Heidelberglaan 100, Utrecht, 3584 CX, the Netherlands

4 Department of Nuclear Medicine, Radboud University Nijmegen Medical Centre, Geert Grooteplein 8, Nijmegen, 6525 GA, the Netherlands

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EJNMMI Research 2013, 3:7  doi:10.1186/2191-219X-3-7

Published: 31 January 2013

Abstract

Background

In 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.

Methods

Effects 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.

Results

Changes 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.

Conclusions

While 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.

Keywords:
Molecular imaging; SPECT; CT; Small animal; Misregistration; Attenuation correction; Quantification