Respiration-induced Attenuation Artifact at PET/CT: Technical Considerations

Abstract

Combined positron emission tomographic (PET)/computed tomographic (CT) scanners allow the use of CT data for attenuation correction of PET images. Eight patients with cancer underwent PET/CT scanning. Transmission scanning was performed with conventional attenuation correction and with CT scanning during maximum inspiration and normal expiration. Image quality was visually compared and fluorine 18 activities were measured in volumes of interest in the lung and myocardium. Analysis of variance for repeated measures revealed a significant decrease (P =.0001) in measured activities between PET images corrected with CT data acquired during maximum inspiration and those corrected with the conventional attenuation correction method or with CT data acquired during normal expiration. Deep inspiration during CT can result in severe deterioration in the final PET image.

Use of coronary calcium score scans from stand-alone multislice computed tomography for attenuation correction of myocardial perfusion SPECT

“…Our results are in line with a recent study by Utsunomiya et al [12], who found that the accuracy of AC was higher with use of a free-breathing and post-exhalation breath-hold protocol during CT scanning than with the inspiration breath-hold protocol. Similarly, Goerres et al [11] reported that the normal postexhalation breath-hold protocol for CT acquisition proved superior compared with deep inspiration for PET-CT image registration. Nevertheless, differences between AC INSP and AC EXP were minimal in our study, as accurate correction for misalignment was performed for each individual scan and AC method.…”

“…Previous studies have suggested that acquisition of the CT attenuation map with free breathing and postexhalation breath-hold resulted in better matching with SPECT and PET images than did acquisition with post-inhalation breath-hold [11,12]. By contrast, CCS is routinely performed during deep inspiration.…”

“…Considering the widespread use of SPECT MPI and the increasing interest in multislice CT for the non-invasive assessment of patients with known or suspected coronary artery disease (CAD), it appears important in view of the upcoming generation of hybrid SPECT-CT scanners to evaluate whether multislice CT data from coronary calcium scoring (CCS) can also be used for generation of reliable attenuation maps to correct MPI SPECT. It has been previously shown that the respiration-dependent change in attenuation values is a possible drawback of CT-based AC [11,12]. The attenuation map obtained with the lower resolution X-ray-based CT data (obtained with a matrix of 128×128) of hybrid SPECT-CT systems represents an average over many breathing cycles.…”

Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans

“…( 8 – 12 ) This is particularly true when the region of interest is at a boundary between tissue types of different densities, most significantly, at the lung/diaphragm interface. ( 11 , 13 , 14 ) It has been reported that using CT data acquired at deep inspiration can produce severe artifacts, ( 15 ) and also that CT protocols using normal expiration breath‐hold or partial breath‐hold acquisition can reduce artifacts in this region. ( 15 , 16 ) Others have proposed that errors due to attenuation correction can be reduced by using a Cine‐CT to produce an averaged (or max) image dataset for correction purposes.…”

PET/CT scanner instrumentation, challenges, and solutions

“…Any form of patient movement and respiratory motion leads to erroneous attenuation correction factors resulting in degraded emission images [29,44]. CT scans often acquire a peak inspiration, whereas PET scans collect an averaged respiratory cycle.…”