Evaluation of attenuation correction in cardiac PET using PET/MR

Lau, Jeffrey; Laforest, Richard; Sotoudeh, Houman; Nie, Xiaolei; Sharma, Shivak; McConathy, Jonathan; Novak, Eric; Priatna, Agus; Gropler, Robert J.; Woodard, Pamela K.

doi:10.1007/s12350-015-0197-1

Cited by 47 publications

(18 citation statements)

References 23 publications

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“…59 ± 7 vs 127 ± 23 minutes). 10 This most recent study confirms the comparability between PET/CT and PET/MR even in the presence of the significant temporal delay between these two scans. Furthermore, the effects of the nonpatient-specific lung attenuation coefficient were found to be not critical for accurate quantification in heart and lesions around the lungs.…”

Section: See Related Article Pp 839-846supporting

confidence: 68%

The foundation layer of quantitative cardiac PET/MRI: Attenuation correction. Again

Nekolla

Cabello

2017

Journal of Nuclear Cardiology

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It is a well-known fact that attenuation correction is the prerequisite of quantification in PET. It is, however, also the (necessarily related, but even more obvious) requirement that a structure-especially one with a significant extent as the heart represents-with homogeneous tracer uptake is depicted precisely like this: homogeneous. This property is one of the confounding factors why cardiac PET is superior to cardiac SPECT even using static imaging. 1 Although the fraction of attenuation-corrected SPECT examinations is increasing, the overwhelming majority of SPECT scans is performed without this procedure. From a plain technical perspective, the necessary information is relatively simply derived from any technique, which assesses the radio-density of the imaged body. Typically, a CT scan is used for this purpose. However, as the energy of the x-ray photons is anywhere between 80 and 140 keV, only a modest extrapolation to the energy of the photons from the radioactive decay (70 to 159 keV) is needed. For PET/CT, it is more challenging: as the energy of the annihilation photons is 511 keV, this extrapolation is a non-trivial task. Fortunately, a relatively simple algorithm based on experimental data can be used with sufficient accuracy, although one should remember that this is still an extrapolation. 2 But PET/MRI further complicates the situation. An extrapolation is not possible anymore as the MRI signal per se does not contain information about the radio-density for photons of any energy whatsoever. Consequently, attenuation correction was considered-and is still in some settings-an obstacle, which can be exacerbated if we consider scatter as it relies on an attenuation map. When we started the development of an algorithm which is now implemented on the vast majority of all commercially available PET/MRI systems, 3 an important element was our knowledge of how attenuation maps from the days of standalone PET scanners looked like ( Figure 1A). The use of rotating Germanium rod sources was timeconsuming and produced-depending on the age of the sources-images of a quality which required a substantial amount of post-processing to reveal the basic structures of the body-typically answering the question: 4 body or air. Still, data from those scanners provided the solid platform of PET's value in research and clinical use in cardiology, neurology, and oncology. A value which was confirmed by PET/CT systems-but never challenged-although the patient throughput increased almost an order of magnitude due to the rapid CT scan. What happened, however, was a change in visual perception ( Figure 1C). As CT images show so much detail especially in high-contrast objects such as bones (and only a few people ever looked at conventional transmission images which never showed bones unless scanning ex vivo specimen for hours, (Figure 1A), there was the anticipation that an MR-based attenuation map should perfectly resemble a CT scan. Fortunately, this is not the case-at least in the thorax, which is of interest here (the hea...

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Section: See Related Article Pp 839-846supporting

confidence: 68%

The foundation layer of quantitative cardiac PET/MRI: Attenuation correction. Again

Nekolla

Cabello

2017

Journal of Nuclear Cardiology

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“…Together with the 19 seconds acquisition time for the DIXON-AC series, acquired in expiratory breathhold, this protocol can be challenging to clinical patients. 16 The impact of these artifacts is expected to be significant for the calculation of the myocardial perfusion, given the non-linear nature of kinetic modeling. 31 The misalignment artifacts may be corrected for through acquisitions of the DIXON-sequence in several respiratory phases, 32,33 or by a subsequent DIXONacquisition at the end of the examination.…”

Section: Discussionmentioning

confidence: 99%

“…14,15 On the other hand, myocardial examinations are not affected by missing bone attenuation, as shown in dual-time-point examinations and simulations of PET/CT examinations. [16][17][18] However, respiratory misalignment between the AC maps and the PET-emission data is a major challenge in myocardial PET-examinations, which causes false-positive findings in up to 40% of the scans. [19][20][21] Increased frequencies of misalignment artifacts are expected in simultaneous cardiac PET/MRI examinations, due to the requirements of breath-hold for the MR-acquisitions.…”

Section: Introductionmentioning

confidence: 99%

Assessment of attenuation correction for myocardial PET imaging using combined PET/MRI

Lassen

Rasul

Beitzke

et al. 2019

Journal of Nuclear Cardiology

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Objective. To evaluate the frequency of artifacts in MR-based attenuation correction (AC) maps and their impact on the quantitative accuracy of PET-based flow and metabolism measurements in a cohort of consecutive heart failure patients undergoing combined PET/MR imaging.Methods. Myocardial viability studies were performed in 20 patients following a dualtracer protocol involving the assessment of myocardial perfusion ( 13 N-NH 3 : 813 ± 86 MBq) and metabolism ( 18 F-FDG: 335 ± 38 MBq). All acquisitions were performed using a fully-integrated PET/MR system, with standard DIXON-attenuation correction (DIXON-AC) mapping for each PET scan. All AC maps were examined for spatial misalignment with the emission data, total lung volume, susceptibility artifacts, and tissue inversion (TI). Misalignment and susceptibility artifacts were corrected using rigid co-registration and retrospective filling of the susceptibility-induced gaps, respectively. The effects of the AC artifacts were evaluated by relative difference measures and perceived changes in clinical interpretations.Results. Average respiratory misalignment of (7 ± 4) mm of the PET-emission data and the AC maps was observed in 18 (90%) patients. Substantial changes in the lung volumes of the AC maps were observed in the test-retest analysis (ratio: 1.0 ± 0.2, range: 0.8-1.4). Susceptibility artifacts were observed in 10 (50%) patients, while six (30%) patients had TI artifacts. Average differences of 14 ± 10% were observed for PET images reconstructed with the artifactual AC maps. The combined artifact effects caused false-positive findings in three (15%) patients.Conclusion. Standard DIXON-AC maps must be examined carefully for artifacts and misalignment effects prior to AC correction of cardiac PET/MRI studies in order to avoid misinterpretation of biased perfusion and metabolism readings from the PET data. (J Nucl Cardiol 2017)

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“…This approach was developed largely for oncological indications but has also been evaluated for cardiac PET/MR imaging (19). However, on the basis of our initial experience, we hypothesized that when imaging the heart, breath-held imaging, even at end-expiration, does not accurately correspond to the time-averaged location of the heart during free-breathing PET acquisitions and that this results in mismatch between the PET emission and attenuation data and the potential for image artifacts.…”

Section: Methodsmentioning

confidence: 99%

Coronary Artery PET/MR Imaging

Robson

Dweck

Trivieri

et al. 2017

JACC: Cardiovascular Imaging

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OBJECTIVES The aims of this study were to describe the authors’ initial experience with combined coronary artery positron emission tomographic (PET) and magnetic resonance (MR) imaging using 18F-fluorodeoxyglucose (18F-FDG) and 18F-sodium fluoride (18F-NaF) radiotracers, describe common problems and their solutions, and demonstrate the feasibility of coronary PET/MR imaging in appropriate patients. BACKGROUND Recently, PET imaging has been applied to the aortic valve and regions of atherosclerosis. 18F-FDG PET imaging has become established for imaging inflammation in atherosclerosis in the aorta and carotid arteries. Moreover, 18F-NaF has emerged as a novel tracer of active microcalcification in the aortic valve and coronary arteries. Coronary PET imaging remains challenging because of the small caliber of the vessels and their complex motion. Currently, most coronary imaging uses combined PET and computed tomographic imaging, but there is increasing enthusiasm for PET/MR imaging because of its reduced radiation, potential to correct for motion, and the complementary information available from cardiac MR in a single scan. METHODS Twenty-three patients with diagnosed or documented risk factors for coronary artery disease underwent either 18F-FDG or 18F-NaF PET/MR imaging. Standard breath-held MR-based attenuation correction was compared with a novel free-breathing approach. The impact on PET image artifacts and the interpretation of vascular uptake were evaluated semiquantitatively by expert readers. Moreover, PET reconstructions with more algorithm iterations were compared visually and by target-to-background ratio. RESULTS Image quality was significantly improved by novel free-breathing attenuation correction. Moreover, conspicuity of coronary uptake was improved by increasing the number of algorithm iterations from 3 to 6. Elevated radiotracer uptake could be localized to individual coronary lesions using both 18F-FDG (n = 1, maximal target-to-background ratio = 1.61) and 18F-NaF (n = 7, maximal target-to-background ratio = 1.55 ± 0.37), including in 1 culprit plaque post–myocardial infarction confirmed by myocardial late gadolinium enhancement. CONCLUSIONS The authors provide the first demonstration of successful, low-radiation (7.2 mSv) PET/MR imaging of inflammation and microcalcification activity in the coronary arteries. However, this requires specialized approaches tailored to coronary imaging for both attenuation correction and PET reconstruction.

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Evaluation of attenuation correction in cardiac PET using PET/MR

Abstract: Myocardial SUVs PET imaging using MR for AC shows excellent correlation with myocardial SUVs obtained by standard PET/CT imaging. The 2-point Dixon VIBE MR technique can be used for AC in simultaneous PET/MR data acquisition.

Cited by 47 publications

References 23 publications

The foundation layer of quantitative cardiac PET/MRI: Attenuation correction. Again

The foundation layer of quantitative cardiac PET/MRI: Attenuation correction. Again

Assessment of attenuation correction for myocardial PET imaging using combined PET/MRI

Coronary Artery PET/MR Imaging

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