Respiration-Averaged CT for Attenuation Correction in Canine Cardiac PET/CT

Abstract

Heart disease is a leading cause of death in North America. With the increased availability of PET/CT scanners, CT is now commonly used as a transmission source for attenuation correction. Because of the differences in scan duration between PET and CT, respiration-induced motion can create inconsistencies between the PET and CT data and lead to incorrect attenuation correction and, thus, artifacts in the final reconstructed PET images. This study compared respiration-averaged CT and 4-dimensional (4D) CT for attenuation correction of cardiac PET in an in vivo canine model as a means of removing these inconsistencies. Methods: Five dogs underwent respiration-gated cardiac 18 F-FDG PET and 4D CT. The PET data were reconstructed with 3 methods of attenuation correction that differed only in the CT data used: The first method was single-phase CT at either end-expiration, end-inspiration, or the middle of a breathing cycle; the second was respiration-averaged CT, which is CT temporally averaged over the entire respiratory cycle; and the third was phase-matched CT, in which each PET phase is corrected with the matched phase from 4D CT. After reconstruction, the gated PET images were summed to produce an ungated image. Polar plots of the PET heart images were generated, and percentage differences were calculated with respect to the phase-matched correction for each dog. The difference maps were then averaged over the 5 dogs. Results: For single-phase CT correction at end-expiration, end-inspiration, and mid cycle, the maximum percentage differences were 11% 6 4%, 7% 6 3%, and 5% 6 2%, respectively. Conversely, the maximum difference for attenuation correction with respiration-averaged CT data was only 1.6% 6 0.7%. Conclusion: Respirationaveraged CT correction produced a maximum percentage difference 7 times smaller than that obtained with end-expiration single-phase correction. This finding indicates that using respiration-averaged CT may accurately correct for attenuation on respiration-ungated cardiac PET.

Decreased Perfusion in the Lateral Wall of the Left Ventricle in PET/CT Studies with 13N-Ammonia: Evaluation in Healthy Adults

“…However, this phenomenon appears to be more common with PET/CT scanners (1)(2)(3)(4)(5)(6)(7)(8). In our patients, 41% showed misalignment at the left heart border at rest and 62% showed misalignment at the left heart border at stress.…”

“…The routine CT-acquired density map of the heart is acquired in a much shorter time and results in less blurring. Because the heart moves within the chest with respiration and there is a large difference in density between the heart and adjacent lung, attenuation correction artifacts in the lateral wall of the left ventricle have become common with PET/CT (1)(2)(3)(4)(5)(6).…”

“…The cause of this finding has never been fully explained, leaving the possibility that the lateral wall defect is a normal finding in PET of the heart with 13 Nammonia (4). In addition, many studies of the lateral wall defect have used patients with known or likely coronary artery disease, making it difficult to separate artifact from disease with certainty (1,3,8).…”

Feasibility of using respiration‐averaged MR images for attenuation correction of cardiac PET/MR imaging

“…For cardiac PET/CT attenuation correction, the use of respiration‐averaged CT (ACT) images has been reported to reduce respiratory motion‐induced misalignment of PET and CT images 13 , 16 , 17 . Similarly, we posit that using respiration‐averaged MR (AMR) images for attenuation correction could reduce misalignment between cardiac PET and MR data and thus reduce myocardial perfusion artifacts in PET/MR images.…”

Attenuation Correction Strategies for Positron Emission Tomography/Computed Tomography and 4-Dimensional Positron Emission Tomography/Computed Tomography

“…Many potential solutions have been suggested to accommodate differences between breathing patterns including retrospective AC using free breathing CT, 48 the use of optimal CT acquisition protocols, 49,50 respiratory averaged CT, 42,[51][52][53]59 interpolated average CT, 54,55 phased CT acquisitions, [56][57][58] cine CT acquisition, 59 respiratory correlated acquisitions, [60][61][62] deep-inspiration breath-hold acquisition, 44,[63][64][65] and the use of respiratory-gated PET/CT acquisitions. [66][67][68][69][70][71][72][73][74][75] One approach to improve registration between the CT and the PET data is to bring the temporal resolution of the CT images to that of the PET data.…”