Effects of attenuation map accuracy on attenuation-corrected micro-SPECT images.
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.
Section Radiation, Detection & Medical Imaging, Delft University of Technology, Mekelweg 15, Delft, 2629 JB, the Netherlands. c.wu@tudelft.nl.
Chao
C
Wu
Hugo A
HA
Gratama van Andel
Peter
P
Laverman
Otto C
OC
Boerman
Freek J
FJ
Beekman