Breath-hold CT attenuation correction for quantitative cardiac SPECT

Abstract

BackgroundAttenuation correction of a single photon emission computed tomography (SPECT) image is possible using computed tomography (CT)-based attenuation maps with hybrid SPECT/CT. CT attenuation maps acquired during breath holding can be misaligned with SPECT, generating artifacts in the reconstructed images. The purpose of this study was to investigate the effects of respiratory phase during breath-hold CT acquisition on attenuation correction of cardiac SPECT imaging.MethodsA series of 201Tl-emission and 99mTc-based transmission computed tomography (TCT) scans was carried out along with CT-attenuation scans on 11 young normal volunteers using a hybrid SPECT/CT scanner. The CT scans were performed at three respiratory phases: end-inspiration (INS), end-expiration (EXP), and the midpoint (MID) between these phases. Using alignment parameters between attenuation maps and SPECT images without attenuation or scatter corrections, quantitative SPECT images were reconstructed, including corrections for attenuation and scatter. Regional radioactivity concentrations normalized by the subjects’ weights were compared between CT- and TCT-based attenuation correction techniques.ResultsSPECT images with CT attenuation maps at the EXP phase showed significant differences in regional weight-normalized radioactivity concentrations relative to the images using the other attenuation maps (p < 0.05), as well as systematic positive bias errors, compared to TCT-based images for all myocardial segments, 5.7% ± 2.7% (1.9% to 10.0%). No significant differences in regional weight-normalized radioactivity concentrations were observed between images with CT attenuation maps at MID and INS phases or between these and the TCT-based images, but regional tendencies were found: for anterior to anterolateral segment, positive bias of 5.0% ± 2.2% (1.3% to 8.1%) and 5.6% ± 1.9% (2.6% to 8.5%) and for inferior to inferoseptal segment, negative bias of −5.3% ± 2.6% (−9.1% to −1.7%) and −4.6% ± 2.5% (−8.8% to −1.5%) for the MID and INS phases, respectively.ConclusionsUse of breath-hold CT attenuation maps at INS and MID phases for attenuation and scatter corrections demonstrated accurate quantitative images that would prove beneficial in cardiac SPECT/CT studies.

Respiration-averaged CT versus standard CT attenuation map for correction of 18F-sodium fluoride uptake in coronary atherosclerotic lesions on hybrid PET/CT

“…Despite improvements in the test-retest reproducibility and reclassification of singular lesions following the introduction of sophisticated motion correction techniques, the quantitative accuracy might still be impaired by respiratory translations of the PET images during the 30-min long PET acquisitions. Current attenuation correction protocols employ a singlephase CT scan (free breathing, or end-expiratory breathing) (5,(12)(13)(14)(15). The use of single-phase CTAC maps may change the observed uptake patterns in the heart, with deviations between 6% in canine models (27), and as much as 35% in human studies (28).…”

“…To ameliorate this problem, realignment of the CTAC maps and PET emission data before PET image reconstruction is sometimes required to obtain optimal predictive value (11). However, single-phase CTAC maps affect the quantitative accuracy of myocardial viability studies owing to the continuous respiratory translations during the PET emission acquisitions (12)(13)(14)(15). Previous studies employing respiratory averaged CTAC maps (RACTAC), obtained from cine-CT scans can improve the quantitative accuracy in myocardial perfusion and viability studies (16,17).…”

Accurate localization of incidental findings on the computed tomography attenuation correction image

“…Methods of correction, including respiratory gating, deep-inspiration-breath-hold (DIBH), motion correction and post processing methods, have been discussed to correct for these errors [30]. Furthermore the phase of breathing (inspiration, mid-breath, expirations) also has been found to have a significant bearing on AC [30,32].…”

Recent advances in cardiac SPECT instrumentation and imaging methods

“…In the presence of CT-SPECT mismatch, very different conclusions were drawn from studies that investigated the optimal CT acquisition that mitigates mismatch artifacts. In a study with the gold standard of transmission-based attenuation map that is motion blurred and matches with SPECT data (Koshino et al 2012), CT attenuation maps acquired at end-expiration led to SPECT images with positive errors in radioactivity concentration, while using attenuation maps from end-inspiration and midpoint between the two phases showed accurate quantification. However, in a phantom study investigating various SPECT/CT scanners (Konik et al 2013), the mismatch artifacts in the SPECT images by using the attenuation maps derived from helical CT could be mitigated by performing breath-hold acquisition at end-expiration.…”