PET/MR Imaging: Technical Aspects and Potential Clinical Applications

Torigian, Drew A.; Zaidi, Habib; Kwee, Thomas C.; Saboury, Babak; Udupa, Jayaram K.; Cho, Zang-Hee; Alavi, Abass

doi:10.1148/radiol.13121038

Cited by 206 publications

(130 citation statements)

References 116 publications

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“…Hybr id PET/MR imaging has recently emerged as a new modality enabling simultaneous molecular and morphologic assessment of a variety of physiopathologic conditions (1). Over the last 2 decades, PET/MR technology has experienced considerable technical advances toward addressing the challenges encountered in system design and quantitative performance.…”

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confidence: 99%

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

Mehranian

Zaidi

2015

J Nucl Med

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Time-of-flight (TOF) PET/MR imaging is an emerging imaging technology with great capabilities offered by TOF to improve image quality and lesion detectability. We assessed, for the first time, the impact of TOF image reconstruction on PET quantification errors induced by MR imaging-based attenuation correction (MRAC) using simulation and clinical PET/CT studies. Methods: Standard 4-class attenuation maps were derived by segmentation of CT images of 27 patients undergoing PET/CT examinations into background air, lung, soft-tissue, and fat tissue classes, followed by the assignment of predefined attenuation coefficients to each class. For each patient, 4 PET images were reconstructed: non-TOF and TOF both corrected for attenuation using reference CT-based attenuation correction and the resulting 4-class MRAC maps. The relative errors between non-TOF and TOF MRAC reconstructions were compared with their reference CT-based attenuation correction reconstructions. The bias was locally and globally evaluated using volumes of interest (VOIs) defined on lesions and normal tissues and CT-derived tissue classes containing all voxels in a given tissue, respectively. The impact of TOF on reducing the errors induced by metal-susceptibility and respiratory-phase mismatch artifacts was also evaluated using clinical and simulation studies. Results: Our results show that TOF PET can remarkably reduce attenuation correction artifacts and quantification errors in the lungs and bone tissues. Using classwise analysis, it was found that the non-TOF MRAC method results in an error of -3.4% ± 11.5% in the lungs and -21.8% ± 2.9% in bones, whereas its TOF counterpart reduced the errors to -2.9% ± 7.1% and -15.3% ± 2.3%, respectively. The VOI-based analysis revealed that the non-TOF and TOF methods resulted in an average overestimation of 7.5% and 3.9% in or near lung lesions (n 5 23) and underestimation of less than 5% for soft tissue and in or near bone lesions (n 5 91). Simulation results showed that as TOF resolution improves, artifacts and quantification errors are substantially reduced. Conclusion: TOF PET substantially reduces artifacts and improves significantly the quantitative accuracy of standard MRAC methods. Therefore, MRAC should be less of a concern on future TOF PET/MR scanners with improved timing resolution. Hybr id PET/MR imaging has recently emerged as a new modality enabling simultaneous molecular and morphologic assessment of a variety of physiopathologic conditions (1). Over the last 2 decades, PET/MR technology has experienced considerable technical advances toward addressing the challenges encountered in system design and quantitative performance. With the advent of avalanche photodiodes and silicon photomultipliers, the challenge of mutual compatibility between PET and MR subsystems has now been well addressed, thus paving the way toward fully integrated time-of-flight (TOF) PET/MR systems (2). However, accurate PET quantification using MR imaging-based attenuation correction (MRAC) remains a major challenge (3)....

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confidence: 99%

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

Mehranian

Zaidi

2015

J Nucl Med

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“…The most straightforward approach adopted the configuration of clinical PET/ CT systems, where separate PET and MR scanners were arranged in tandem to enable sequential data acquisition in space and time. This less challenging design concept was adopted as a first step to gain experience and establish the clinical role of this hybrid modality while waiting for mature and economically practical simultaneous whole-body PET/MRI units to become available [5]. Figure 1 shows potential design concepts of combined PET/MRI systems.…”

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confidence: 99%

“…These technologic advances enabled the design of more advanced PET/MR units dedicated initially to brain and more recently for whole-body imaging, thus allowing a practical exploration of the clinical potential of this hybrid technology [5].…”

Section: Introductionmentioning

confidence: 99%

A Pivotal Time for Hybrid PET/MR Imaging Technology

Zaidi

2013

Journal of the American College of Radiology

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“…The advent of hybrid positron emission tomography (PET)/magnetic resonance (MR) imaging systems has brought the potential of superior diagnostic performance over PET/CT (computed tomography) in certain applications, 1 , 2 , 3 , 4 , 5 including cardiac imaging 6 , 7 , 8 , 9 , 10 . However, respiratory motion can compromise the quantification of cardiac PET data using MR data.…”

Section: Introductionmentioning

confidence: 99%

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

Pan

2015

J Applied Clin Med Phys

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Cardiac imaging is a promising application for combined PET/MR imaging. However, current MR imaging protocols for whole‐body attenuation correction can produce spatial mismatch between PET and MR‐derived attenuation data owing to a disparity between the two modalities' imaging speeds. We assessed the feasibility of using a respiration‐averaged MR (AMR) method for attenuation correction of cardiac PET data in PET/MR images. First, to demonstrate the feasibility of motion imaging with MR, we used a 3T MR system and a two‐dimensional fast spoiled gradient‐recalled echo (SPGR) sequence to obtain AMR images of a moving phantom. Then, we used the same sequence to obtain AMR images of a patient's thorax under free‐breathing conditions. MR images were converted into PET attenuation maps using a three‐class tissue segmentation method with two sets of predetermined CT numbers, one calculated from the patient‐specific (PS) CT images and the other from a reference group (RG) containing 54 patient CT datasets. The MR‐derived attenuation images were then used for attenuation correction of the cardiac PET data, which were compared to the PET data corrected with average CT (ACT) images. In the myocardium, the voxel‐by‐voxel differences and the differences in mean slice activity between the AMR‐corrected PET data and the ACT‐corrected PET data were found to be small (less than 7%). The use of AMR‐derived attenuation images in place of ACT images for attenuation correction did not affect the summed stress score. These results demonstrate the feasibility of using the proposed SPGR‐based MR imaging protocol to obtain patient AMR images and using those images for cardiac PET attenuation correction. Additional studies with more clinical data are warranted to further evaluate the method.PACS number: 87.57.uk

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PET/MR Imaging: Technical Aspects and Potential Clinical Applications

Abstract: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13121038/-/DC1.

Cited by 206 publications

References 116 publications

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

Impact of Time-of-Flight PET on Quantification Errors in MR Imaging–Based Attenuation Correction

A Pivotal Time for Hybrid PET/MR Imaging Technology

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

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