Cine CT for Attenuation Correction in Cardiac PET/CT

Abstract

In dual-modality PET/CT systems, the CT scan provides the attenuation map for PET attenuation correction. The current clinical practice of obtaining a single helical CT scan provides only a snapshot of the respiratory cycle, whereas PET occurs over multiple respiratory cycles. Misalignment of the attenuation map and emission image because of respiratory motion causes errors in the attenuation correction factors and artifacts in the attenuationcorrected PET image. To rectify this problem, we evaluated the use of cine CT, which acquires multiple low-dose CT images during a respiratory cycle. We evaluated the average and the intensity-maximum image of cine CT for cardiac PET attenuation correction. Methods: Cine CT data and cardiac PET data were acquired from a cardiac phantom and from multiple patient studies. The conventional helical CT, cine CT, and PET data of an axially translating phantom were evaluated with and without respiratory motion. For the patient studies, we acquired 2 cine CT studies for each PET acquisition in a rest-stress 13 N-ammonia protocol. Three readers visually evaluated the alignment of 74 attenuation image sets versus the corresponding emission image and determined whether the alignment provided acceptable or unacceptable attenuation-corrected PET images. Results: In the phantom study, the attenuation correction from helical CT caused a major artifactual defect in the lateral wall on the PET image. The attenuation correction from the average and from the intensity-maximum cine CT images reduced the defect by 20% and 60%, respectively. In the patient studies, 77% of the cases using the average of the cine CT images had acceptable alignment and 88% of the cases using the intensity maximum of the cine CT images had acceptable alignment. Conclusion: Cine CT offers an alternative to helical CT for compensating for respiratory motion in the attenuation correction of cardiac PET studies. Phantom studies suggest that the average and the intensity maximum of the cine CT images can reduce potential respirationinduced misalignment errors in attenuation correction. Patient studies reveal that cine CT provides acceptable alignment in most cases and suggest that the intensity-maximum cine image offers a more robust alternative to the average cine image. PET combined with CT in an integrated PET/CT scanner offers a single-study, noninvasive technique for the diagnosis of coronary artery disease. The integrated modalities provide distinct and complementary information: PET offers functional measurement of myocardial perfusion and metabolism, whereas contrast-enhanced CT angiography offers structural assessment of coronary anatomy and atherosclerotic burden (1,2).A limitation with cardiac PET on a PET/CT system is that the PET attenuation map formed from a helical CT acquisition represents a snapshot of the respiratory cycle, whereas the PET image is acquired over multiple respirations. The potential attenuation and emission misalignment dramatically reduces the accuracy of attenuation correction, leading...

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

“…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).…”

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.…”