Abstract
The introduction of positron emission tomography/computed tomography (PET/CT), particularly with F-18 fluorodeoxyglucose, has transformed disease management, especially in oncology, marking a major breakthrough in nuclear medicine. Since its advent, PET/CT has been widely adopted as both a primary and complementary imaging modality. The functional data from PET, integrated with anatomical details from CT, has facilitated more effective disease management. Advancements in PET and CT technologies have enhanced imaging outcomes, but limitations of CT, such as inadequate soft tissue contrast and ionizing radiation exposure, remain. In response, PET/magnetic resonance imaging (MRI) has emerged, offering high tissue contrast and additional functional data, addressing CT’s shortcomings. However, PET/MRI introduces new challenges, including attenuation correction and signal issues in bone and lung imaging. Evaluating lung lesions is still challenging, though progress has been made with short echo time sequences. The distinct imaging characteristics and artifacts of MRI necessitate adaptation, requiring familiarity with various sequences and proper imaging protocols. The MRI component also introduces safety concerns that must be addressed with proper procedures and staff training. Additionally, the high cost of PET/MRI limits its availability to major research centers. Despite these challenges, PET/MRI represents a new milestone in nuclear medicine, generating excitement in the field. Ongoing developments are expected to address current issues, but understanding existing challenges and pitfalls is essential for accurate interpretation. This review discusses the general challenges, critical areas of concern, and potential pitfalls associated with PET/MRI.
Keywords: PET/MRI, attenuation, artifact, lung, SUV
References
Phelps ME, Hoffman EJ, Mullani NA, Ter-Pogossian MM. Application of annihilation coincidence detection to transaxial reconstruction tomography. J Nucl Med. 1975;16:210-224.
Townsend DW. Combined positron emission tomography-computed tomography: the historical perspective. Semin Ultrasound CT MR. 2008;29:232-235.
Afaq A, Faul D, Chebrolu VV, et al. Pitfalls on PET/MRI. Semin Nucl Med. 2021;51:529-539.
Keller SH, Holm S, Hansen AE, et al. Image artifacts from MR-based attenuation correction in clinical, whole-body PET/MRI. MAGMA. 2013;26:173-181.
Schramm G, Rigie D, Vahle T, et al. Approximating anatomically-guided PET reconstruction in image space using a convolutional neural network. Neuroimage. 2021;224:117399.
Mehranian A, Zaidi H. Clinical assessment of emission- and segmentation-based MR-guided attenuation correction in whole-body time-of-flight PET/MR imaging. J Nucl Med. 2015;56:877-883.
Jung JH, Choi Y, Im KC. PET/MRI: Technical challenges and recent advances. Nucl Med Mol Imaging. 2016;50:3-12.
Delso G, ter Voert E, de Galiza Barbosa F, Veit-Haibach P. Pitfalls and limitations in simultaneous PET/MRI. Semin Nucl Med. 2015;45:552-559.
Noda C, Ambale Venkatesh B, Wagner JD, Kato Y, Ortman JM, Lima JAC. Primer on commonly occurring MRI artifacts and how to overcome them. Radiographics. 2022;42:E102-E103.
Catana C. Motion correction options in PET/MRI. Semin Nucl Med. 2015;45:212-223.
Ladefoged CN, Hansen AE, Keller SH, et al. Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion. EJNMMI Phys. 2014;1:101.
Schramm G, Maus J, Hofheinz F, et al. Evaluation and automatic correction of metal-implant-induced artifacts in MR-based attenuation correction in whole-body PET/MR imaging. Phys Med Biol. 2014;59:2713-2726.
Koch KM, Brau AC, Chen W, et al. Imaging near metal with a MAVRIC-SEMAC hybrid. Magn Reson Med. 2011;65:71-82.
Morelli JN, Runge VM, Ai F, et al. An image-based approach to understanding the physics of MR artifacts. Radiographics. 2011;31:849-866.
Sim AJ, Kaza E, Singer L, Rosenberg SA. A review of the role of MRI in diagnosis and treatment of early stage lung cancer. Clin Transl Radiat Oncol. 2020;24:16-22.
de Galiza Barbosa F, Geismar JH, Delso G, et al. Pulmonary nodule detection in oncological patients - value of respiratory-triggered, periodically rotated overlapping parallel T2-weighted imaging evaluated with PET/CT-MR. Eur J Radiol. 2018;98:165-170.
Chassagnon G, Martin C, Ben Hassen W, et al. High-resolution lung MRI with ultrashort-TE: 1.5 or 3 Tesla? Magn Reson Imaging. 2019;61:97-103.
Zhu X, Chan M, Lustig M, Johnson KM, Larson PEZ. Iterative motion-compensation reconstruction ultra-short TE (iMoCo UTE) for high-resolution free-breathing pulmonary MRI. Magn Reson Med. 2020;83:1208-1221.
Crimì F, Varotto A, Orsatti G, et al. Lung visualisation on PET/MRI: implementing a protocol with a short echo-time and low flip-angle volumetric interpolated breath-hold examination sequence. Clin Radiol. 2020;75:239.e15-239.e21.
Bae K, Jeon KN, Hwang MJ, et al. Comparison of lung imaging using three-dimensional ultrashort echo time and zero echo time sequences: preliminary study. Eur Radiol. 2019;29:2253-2262.
