MR-based attenuation correction for cardiac FDG PET on a hybrid PET/MRI scanner: comparison with standard CT attenuation correction

Vontobel, Jan; Liga, Riccardo; Possner, Mathias; Clerc, Olivier; Mikulicic, Fran; Veit-Haibach, Patrick; Voert, Edwin E. G. W. ter; Fuchs, Tobias A.; Stehli, Julia; Pazhenkottil, Aju P.; Benz, Dominik C.; Gräni, Christoph; Gaemperli, Oliver; Herzog, Bernhard A.; Buechel, Ronny R.; Kaufmann, Philipp A.

doi:10.1007/s00259-015-3089-3

Cited by 48 publications

(35 citation statements)

References 28 publications

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“…67 ± 13 minutes, D Time = 42 ± 13 minutes) 8 and Vontobel evaluated the approach as implemented on the second commercially available, fully integrated PET/MRI system (n = 23, oncological patients, D Time 46 ± 17 minutes). 9 Lau and colleagues not only confirmed the results using SUV values but also investigated the effects of a variable lung signal (n = 30, oncological patients, time p.i. 59 ± 7 vs 127 ± 23 minutes).…”

Section: See Related Article Pp 839-846supporting

confidence: 48%

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: 48%

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

Nekolla

Cabello

2017

Journal of Nuclear Cardiology

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“…Before each PET scan, MR images were acquired to correct for photon attenuation. Attenuation correction was performed using 2-point Dixon MR images as previously described (16,17). Data acquisition spanned over 10 min and began a few seconds before the 13 N-ammonia injection.…”

Section: Animal Model and Preparationmentioning

confidence: 99%

Arterial CO₂ as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing

et al. 2017

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Myocardial blood flow (MBF) is the critical determinant of cardiac function. However, its response to increases in partial pressure of arterial CO 2 (PaCO 2 ), particularly with respect to adenosine, is not well characterized because of challenges in blood gas control and limited availability of validated approaches to ascertain MBF in vivo. Methods: By prospectively and independently controlling PaCO 2 and combining it with 13 N-ammonia PET measurements, we investigated whether a physiologically tolerable hypercapnic stimulus (;25 mm Hg increase in PaCO 2 ) can increase MBF to that observed with adenosine in 3 groups of canines: without coronary stenosis, subjected to non-flow-limiting coronary stenosis, and after preadministration of caffeine. The extent of effect on MBF due to hypercapnia was compared with adenosine. Results: In the absence of stenosis, mean MBF under hypercapnia was 2.1 6 0.9 mL/min/g and adenosine was 2.2 6 1.1 mL/min/g; these were significantly higher than at rest (0.9 6 0.5 mL/min/g, P , 0.05) and were not different from each other (P 5 0.30). Under left-anterior descending coronary stenosis, MBF increased in response to hypercapnia and adenosine (P , 0.05, all territories), but the effect was significantly lower than in the left-anterior descending coronary territory (with hypercapnia and adenosine; both P , 0.05). Mean perfusion defect volumes measured with adenosine and hypercapnia were significantly correlated (R 5 0.85) and were not different (P 5 0.12). After preadministration of caffeine, a known inhibitor of adenosine, resting MBF decreased; and hypercapnia increased MBF but not adenosine (P , 0.05). Conclusion: Arterial blood CO 2 tension when increased by 25 mm Hg can induce MBF to the same level as a standard dose of adenosine. Prospectively targeted arterial CO 2 has the capability to evolve as an alternative to current pharmacologic vasodilators used for cardiac stress testing.

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“…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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MR-based attenuation correction for cardiac FDG PET on a hybrid PET/MRI scanner: comparison with standard CT attenuation correction

Abstract: Relative myocardial FDG uptake obtained from MR-based attenuation corrected FDG PET is highly comparable to standard CT-based attenuation corrected FDG PET, suggesting interchangeability of both AC techniques.

Cited by 48 publications

References 28 publications

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

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

Arterial CO₂ as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing

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

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MR-based attenuation correction for cardiac FDG PET on a hybrid PET/MRI scanner: comparison with standard CT attenuation correction

Abstract: Relative myocardial FDG uptake obtained from MR-based attenuation corrected FDG PET is highly comparable to standard CT-based attenuation corrected FDG PET, suggesting interchangeability of both AC techniques.

Cited by 48 publications

References 28 publications

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

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

Arterial CO2 as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing

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

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Arterial CO₂ as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing