- Email: [email protected]
MRI: ready for clinical routine?
European Journal of Radiology xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Hybrid imaging with PET/MRI: ready for clinical routine? A R T I C L E I N F O
A B S T R A C T
Keywords: Hybrid imaging PET/MRI Multiparametric imaging
The introduction of integrated PET/MRI imaging combining full magnetic resonance imaging and positron emission tomography is a new milestone in tissue imaging. As usual innovations in clinical practice generate new dilemmas. The questions it poses are: when to use PET/MRI scanning, what radiopharmaceutical to use and how to optimize examination protocols. A range of new radiopharmaceuticals, in addition to 18F-fluorodeoxyglucose (18F-FDG), are now available for assessing and characterizing tissues.
Over the last decade, the rapid adoption of hybrid PET/CT imaging has changed the clinical diagnostic algorithms of many tumorous diseases. Because of relatively poor soft tissue contrast discrimination, computed tomography (CT) is limited in the detail imaging of tissues, such as brain, head and neck tissues, prostate and other pelvic organs. The other inherent problem for CT is the radiation dose burden to the patient. These difficulties are logically projected into the hybrid imaging of PET/CT. Recent advances in scanning techniques of both positron emission tomography (PET) and CT have substantially reduced the dose of ionizing radiation used in examinations. Nevertheless, this dose remains a significant factor in the stochastic effects of radiation, especially in patients undergoing repeated examinations. The introduction of hybrid PET/MRI imaging into clinical practice has opened up the possibility of reducing the radiation dose from hybrid imaging by eliminating the contribution from CT. PET/MRI with integrated 3 T MRI subsystems allows the use of a complete repetoir of diagnostic imaging algorithms. However, there are serious disadvantages associated with the use of PET/MRI. These problems include the length of examination time, which for whole body imaging are not acceptable for many patients and especially for those with acute conditions. Generally, examinations take about 45 min, which is the limit most patients can tolerate. So, the MRI protocols have to be tailored to the patient's condition and ability to remain still in the scanner as well as being capable of answering the clinical question. For PET/MRI optimizing imaging protocols and their appropriate applications are crucial, especially in the light of the competition with PET/CT and non-hybrid MRI. The main questions to be discussed are when it should be used, with what radiopharmaceuticals and how to design the examination protocol. In addition to 18F-fluorodeoxyglucose (18F-FDG), the most frequently used molecule in the PET diagnosis, other molecules can be chosen from the range of available radiopharmaceuticals for assessing tumors. These include: 18F-fluorothymidine (18F-FLT), 18F-fluorocholine (18F-FCH), 18F-fluoro-ethyltyrosine (18F-FET), 18F-fluorodihydroxyphenylalanine (18F-FDOPA), 11C-methionine (11C-MET) or 18F-fluoromisonidazole (18F-FMISO), 68Ga-DOTA derivates, 68Ga-PSMA, also 18F-florbetaben or 18F-flutemetamol for brain amyloid beta imaging. Introducing PET/MRI imaging with simultaneous full magnetic resonance imaging is a challenge in practice. The current scenarios of the PE/MRI are divided in two main streams. The first approach is to decrease the general radiation dose burden to the patients; the second one is to exploit all the advantages of precise multiparametric MRI in addition of the molecular imaging of PET [1]. The typical “dose saving” approach is the indications in children and young adults with malignant diseases [2]. Many need repeat imaging during follow up over long periods because diseases, such as Hodgkin disease or testicular tumors are curable. The dosage of the radiopharmaceutical is an important way of decreasing the total radiation dose. The applied activity of the18F-fluorodeoxyglucose could be effectively reduced to the doses of 2.0–2.5 MBq/kg because the acquisition time for one bed position could be tailored acquisition times of the chosen MR sequences. A combination of basic sequences (e.g. gradient echo T1 sequence like VIBE in two directions and T2 weighted STIR or HASTE sequence) in one position takes about 4–5 min to perform. As a result, the total dosing of radiopharmaceutical can be reduced to levels of 50 MBq in infants. These “dose oriented” protocols could be completed within 25 min and are able to replace PET/CT completely in patients with hematologic malignancies or testicular tumors. There are some typical indications for PET/MRI when metabolic imaging is becoming a part of multiparametric assessment [3]: brain tumors or neurodegenerative disease and tumors of the oral cavity, breast, cervix or prostate. The complete MRI imaging protocol includes the high-resolution images, dynamic post contrast scanning oriented to the pharmacodynamic analysis, advanced diffusion weighted imaging with possibilities of tractography reconstruction or using MR spectroscopy. These multi-parametric imaging protocols are able to replace MRI with assessment of tissue metabolic activity, proliferation, or special substance content. The important value of PET/MRI is the capability to add whole-body evaluation of the tumorous spread in diseases like breast cancers, or its use for tele-radiotherapy planning in cervical or prostate carcinoma [4]. What are the current indications and usage of PET/MRI in the spectrum of the diagnostic procedures? In institutions, where it is used routinely, http://dx.doi.org/10.1016/j.ejrad.2017.05.004 Received 29 March 2017; Received in revised form 30 April 2017; Accepted 3 May 2017 0720-048X/ © 2017 Elsevier B.V. All rights reserved.
European Journal of Radiology xxx (xxxx) xxx–xxx
the number of the performed examinations is usually about 1200 per year. Approximately 1% of all procedures are examinations of children and adolescent. Let me present the example of our institution: the commonest examination is non-target imaging of the head and trunk (about 33%), then about 20% are brain examinations for tumors, neurodegenerative disease and epilepsy, then 15%, combined trunk examination with targeted liver imaging and 15% trunk examination with targeted head and neck examinations. The imaging of the pelvic organs covers about 10% and breast imaging takes about 5%, the rest is left to chest, heart or other examinations. This pattern of indications is based on the dose saving in about one third of patients and the advantage of full diagnostic MRI combined with metabolic imaging in whole body staging in two thirds of patients. Rigorous evaluation of the first years of PET/MRI use is important. There are some technical problems which need to be addressed including truncation artifact due to the in-homogeneity of the magnetic field, attenuation correction mistakes and motion artifacts [5–7]. An additional problem is the limited resolution in lung parenchyma imaging. These technical problems can be solved with active compensation of field inhomogeneity and using the motion correction data acquisition and special sequences able to detect lung lesions smaller than 5 mm. The more important question is when to use PET/CT and when PET/MRI, if you have both options. PET/MRI looks be more effective when both an MRI assessment and PET are needed to assess the whole body spread of disease, but is it cost effective? The installation of PET/MRI equipment needs a huge investment and considerable running expenses. The latter is partially due to the cost of radiopharmaceuticals, which are substantial for standalone PET/MRI equipment, but can be shared in the ideal situation of running PET/MRI and PET/CT side by side. Then as a result of the higher through put radiopharmaceutical expenses could be reduced by almost 50%. An important advantage of such combined suites is that claustrophobic patients can be more easily accommodated. In conclusion, PET/MRI seems to be a promising diagnostic imaging tool with potential for further development in clinical indications and technical efficiency improvements. Its future is part of a general trend towards the personalized medicine approach to diagnostics, therapy decisions and therapy effect assessments. References [1] C.M. Tempany, J. Jayender, T. Kapur, et al., Multimodal imaging for improved diagnosis and treatment of cancers, Cancer 121 (6) (2015) 817–827. [2] J. Grueneisen, L.M. Sawicki, B.M. Schaarschmidt, S. Suntharalingam, S. von der Ropp, A. Wetter, V. Ruhlmann, H.H. Quick, M. Forsting, L. Umutlu, Evaluation of a fast protocol for staging lymphoma patients with integrated PET/MRI, PLoS One 11 (6) (2016) e0157880 Jun 21. [3] A. Jena, S. Taneja, A. Gambhir, A.K. Mishra, M.M. D?souza, S.M. Verma, P.P. Hazari, P. Negi, G.K. Jhadav, S.K. Sogani, Glioma recurrence versus radiation necrosis: single-session multiparametric approach using simultaneous O-(2-18F-fluoroethyl)-L-tyrosine PET/MRI, Clin. Nucl. Med. 41 (5) (2016) 2016 May, e228-e222. [4] W. Atkinson, C. Catana, J.S. Abramson, G. Arabasz, S. McDermott, O. Catalano, V. Muse, M.A. Blake, J. Barnes, M. Shelly, E. Hochberg, B.R. Rosen, A.R. Guimaraes, Hybrid FDG-PET/ MR compared to FDG-PET/CT in adult lymphoma patients, Abdom. Radiol. (NY) 41 (7) (2016) 1338–4138. [5] C. Catana, Motion correction options in PET/MRI, Semin. Nucl. Med. 45 (3) (2015) 212–223. [6] P. Roy, J.K. Lee, Sheikh, W. Lin, Quantitative comparison of misregistration in abdominal and pelvic organs between PET/MRI and PET/CT: effect of mode of acquisition and type of sequence on different organs AJR Am, J. Roentgenol. 205 (2015) 1295–1305. [7] B. Sharma, A. Martin, L. Zerizer, Positron emission tomography-computed tomography in liver imaging semin, Ultrasound CT MR 34 (2013) 66–80.
Jiří Ferda Clinic of the Imaging Methods, University Hospital Plzen, Alej Svobody 80, Plzeň 304 60, Czech Republic E-mail address: [email protected]
2
Contents lists available at ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Hybrid imaging with PET/MRI: ready for clinical routine? A R T I C L E I N F O
A B S T R A C T
Keywords: Hybrid imaging PET/MRI Multiparametric imaging
The introduction of integrated PET/MRI imaging combining full magnetic resonance imaging and positron emission tomography is a new milestone in tissue imaging. As usual innovations in clinical practice generate new dilemmas. The questions it poses are: when to use PET/MRI scanning, what radiopharmaceutical to use and how to optimize examination protocols. A range of new radiopharmaceuticals, in addition to 18F-fluorodeoxyglucose (18F-FDG), are now available for assessing and characterizing tissues.
Over the last decade, the rapid adoption of hybrid PET/CT imaging has changed the clinical diagnostic algorithms of many tumorous diseases. Because of relatively poor soft tissue contrast discrimination, computed tomography (CT) is limited in the detail imaging of tissues, such as brain, head and neck tissues, prostate and other pelvic organs. The other inherent problem for CT is the radiation dose burden to the patient. These difficulties are logically projected into the hybrid imaging of PET/CT. Recent advances in scanning techniques of both positron emission tomography (PET) and CT have substantially reduced the dose of ionizing radiation used in examinations. Nevertheless, this dose remains a significant factor in the stochastic effects of radiation, especially in patients undergoing repeated examinations. The introduction of hybrid PET/MRI imaging into clinical practice has opened up the possibility of reducing the radiation dose from hybrid imaging by eliminating the contribution from CT. PET/MRI with integrated 3 T MRI subsystems allows the use of a complete repetoir of diagnostic imaging algorithms. However, there are serious disadvantages associated with the use of PET/MRI. These problems include the length of examination time, which for whole body imaging are not acceptable for many patients and especially for those with acute conditions. Generally, examinations take about 45 min, which is the limit most patients can tolerate. So, the MRI protocols have to be tailored to the patient's condition and ability to remain still in the scanner as well as being capable of answering the clinical question. For PET/MRI optimizing imaging protocols and their appropriate applications are crucial, especially in the light of the competition with PET/CT and non-hybrid MRI. The main questions to be discussed are when it should be used, with what radiopharmaceuticals and how to design the examination protocol. In addition to 18F-fluorodeoxyglucose (18F-FDG), the most frequently used molecule in the PET diagnosis, other molecules can be chosen from the range of available radiopharmaceuticals for assessing tumors. These include: 18F-fluorothymidine (18F-FLT), 18F-fluorocholine (18F-FCH), 18F-fluoro-ethyltyrosine (18F-FET), 18F-fluorodihydroxyphenylalanine (18F-FDOPA), 11C-methionine (11C-MET) or 18F-fluoromisonidazole (18F-FMISO), 68Ga-DOTA derivates, 68Ga-PSMA, also 18F-florbetaben or 18F-flutemetamol for brain amyloid beta imaging. Introducing PET/MRI imaging with simultaneous full magnetic resonance imaging is a challenge in practice. The current scenarios of the PE/MRI are divided in two main streams. The first approach is to decrease the general radiation dose burden to the patients; the second one is to exploit all the advantages of precise multiparametric MRI in addition of the molecular imaging of PET [1]. The typical “dose saving” approach is the indications in children and young adults with malignant diseases [2]. Many need repeat imaging during follow up over long periods because diseases, such as Hodgkin disease or testicular tumors are curable. The dosage of the radiopharmaceutical is an important way of decreasing the total radiation dose. The applied activity of the18F-fluorodeoxyglucose could be effectively reduced to the doses of 2.0–2.5 MBq/kg because the acquisition time for one bed position could be tailored acquisition times of the chosen MR sequences. A combination of basic sequences (e.g. gradient echo T1 sequence like VIBE in two directions and T2 weighted STIR or HASTE sequence) in one position takes about 4–5 min to perform. As a result, the total dosing of radiopharmaceutical can be reduced to levels of 50 MBq in infants. These “dose oriented” protocols could be completed within 25 min and are able to replace PET/CT completely in patients with hematologic malignancies or testicular tumors. There are some typical indications for PET/MRI when metabolic imaging is becoming a part of multiparametric assessment [3]: brain tumors or neurodegenerative disease and tumors of the oral cavity, breast, cervix or prostate. The complete MRI imaging protocol includes the high-resolution images, dynamic post contrast scanning oriented to the pharmacodynamic analysis, advanced diffusion weighted imaging with possibilities of tractography reconstruction or using MR spectroscopy. These multi-parametric imaging protocols are able to replace MRI with assessment of tissue metabolic activity, proliferation, or special substance content. The important value of PET/MRI is the capability to add whole-body evaluation of the tumorous spread in diseases like breast cancers, or its use for tele-radiotherapy planning in cervical or prostate carcinoma [4]. What are the current indications and usage of PET/MRI in the spectrum of the diagnostic procedures? In institutions, where it is used routinely, http://dx.doi.org/10.1016/j.ejrad.2017.05.004 Received 29 March 2017; Received in revised form 30 April 2017; Accepted 3 May 2017 0720-048X/ © 2017 Elsevier B.V. All rights reserved.
European Journal of Radiology xxx (xxxx) xxx–xxx
the number of the performed examinations is usually about 1200 per year. Approximately 1% of all procedures are examinations of children and adolescent. Let me present the example of our institution: the commonest examination is non-target imaging of the head and trunk (about 33%), then about 20% are brain examinations for tumors, neurodegenerative disease and epilepsy, then 15%, combined trunk examination with targeted liver imaging and 15% trunk examination with targeted head and neck examinations. The imaging of the pelvic organs covers about 10% and breast imaging takes about 5%, the rest is left to chest, heart or other examinations. This pattern of indications is based on the dose saving in about one third of patients and the advantage of full diagnostic MRI combined with metabolic imaging in whole body staging in two thirds of patients. Rigorous evaluation of the first years of PET/MRI use is important. There are some technical problems which need to be addressed including truncation artifact due to the in-homogeneity of the magnetic field, attenuation correction mistakes and motion artifacts [5–7]. An additional problem is the limited resolution in lung parenchyma imaging. These technical problems can be solved with active compensation of field inhomogeneity and using the motion correction data acquisition and special sequences able to detect lung lesions smaller than 5 mm. The more important question is when to use PET/CT and when PET/MRI, if you have both options. PET/MRI looks be more effective when both an MRI assessment and PET are needed to assess the whole body spread of disease, but is it cost effective? The installation of PET/MRI equipment needs a huge investment and considerable running expenses. The latter is partially due to the cost of radiopharmaceuticals, which are substantial for standalone PET/MRI equipment, but can be shared in the ideal situation of running PET/MRI and PET/CT side by side. Then as a result of the higher through put radiopharmaceutical expenses could be reduced by almost 50%. An important advantage of such combined suites is that claustrophobic patients can be more easily accommodated. In conclusion, PET/MRI seems to be a promising diagnostic imaging tool with potential for further development in clinical indications and technical efficiency improvements. Its future is part of a general trend towards the personalized medicine approach to diagnostics, therapy decisions and therapy effect assessments. References [1] C.M. Tempany, J. Jayender, T. Kapur, et al., Multimodal imaging for improved diagnosis and treatment of cancers, Cancer 121 (6) (2015) 817–827. [2] J. Grueneisen, L.M. Sawicki, B.M. Schaarschmidt, S. Suntharalingam, S. von der Ropp, A. Wetter, V. Ruhlmann, H.H. Quick, M. Forsting, L. Umutlu, Evaluation of a fast protocol for staging lymphoma patients with integrated PET/MRI, PLoS One 11 (6) (2016) e0157880 Jun 21. [3] A. Jena, S. Taneja, A. Gambhir, A.K. Mishra, M.M. D?souza, S.M. Verma, P.P. Hazari, P. Negi, G.K. Jhadav, S.K. Sogani, Glioma recurrence versus radiation necrosis: single-session multiparametric approach using simultaneous O-(2-18F-fluoroethyl)-L-tyrosine PET/MRI, Clin. Nucl. Med. 41 (5) (2016) 2016 May, e228-e222. [4] W. Atkinson, C. Catana, J.S. Abramson, G. Arabasz, S. McDermott, O. Catalano, V. Muse, M.A. Blake, J. Barnes, M. Shelly, E. Hochberg, B.R. Rosen, A.R. Guimaraes, Hybrid FDG-PET/ MR compared to FDG-PET/CT in adult lymphoma patients, Abdom. Radiol. (NY) 41 (7) (2016) 1338–4138. [5] C. Catana, Motion correction options in PET/MRI, Semin. Nucl. Med. 45 (3) (2015) 212–223. [6] P. Roy, J.K. Lee, Sheikh, W. Lin, Quantitative comparison of misregistration in abdominal and pelvic organs between PET/MRI and PET/CT: effect of mode of acquisition and type of sequence on different organs AJR Am, J. Roentgenol. 205 (2015) 1295–1305. [7] B. Sharma, A. Martin, L. Zerizer, Positron emission tomography-computed tomography in liver imaging semin, Ultrasound CT MR 34 (2013) 66–80.
Jiří Ferda Clinic of the Imaging Methods, University Hospital Plzen, Alej Svobody 80, Plzeň 304 60, Czech Republic E-mail address: [email protected]
2