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Integrated whole body MR/PET: where are we?

Yoo HJ, Lee JS, Lee JM - Korean J Radiol (2015)

Bottom Line: This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions.Various early clinical applications of integrated MR/PET are also addressed.Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Seoul National University Hospital, Seoul 110-744, Korea.

ABSTRACT
Whole body integrated magnetic resonance imaging (MR)/positron emission tomography (PET) imaging systems have recently become available for clinical use and are currently being used to explore whether the combined anatomic and functional capabilities of MR imaging and the metabolic information of PET provide new insight into disease phenotypes and biology, and provide a better assessment of oncologic diseases at a lower radiation dose than a CT. This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions. Various early clinical applications of integrated MR/PET are also addressed. Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

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Related in: MedlinePlus

66-year-old man with 3.7-cm lung mass (not shown) in right lower lobe.A. Axial, post-contrast, three-dimensional volumetric interpolated breath-hold examination image showed two small right interlobar lymph nodes (arrows). B. Axial fused FDG-MR/PET image showed increased FDG uptake in interlobar nodes (SUVmax: 4.4 and 3.8). Axial, DWI (b = 400) (C) and ADC map showed diffusion restriction in two lymph nodes (D). Concordant findings of right interlobar lymph nodes on ADC map and on fused MR/PET image increased our confidence in reporting right interlobar lymph-node metastasis, and pathology results confirmed right interlobar lymph-node metastasis. ADC = apparent diffusion coefficient, DWI = diffusion-weighted image, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value
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Figure 5: 66-year-old man with 3.7-cm lung mass (not shown) in right lower lobe.A. Axial, post-contrast, three-dimensional volumetric interpolated breath-hold examination image showed two small right interlobar lymph nodes (arrows). B. Axial fused FDG-MR/PET image showed increased FDG uptake in interlobar nodes (SUVmax: 4.4 and 3.8). Axial, DWI (b = 400) (C) and ADC map showed diffusion restriction in two lymph nodes (D). Concordant findings of right interlobar lymph nodes on ADC map and on fused MR/PET image increased our confidence in reporting right interlobar lymph-node metastasis, and pathology results confirmed right interlobar lymph-node metastasis. ADC = apparent diffusion coefficient, DWI = diffusion-weighted image, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value

Mentions: For the evaluation of locoregional lymph-node metastasis, cross-sectional imaging modalities, including CT and MR imaging, are dependent mainly on the size and shape of lymph nodes in order to differentiate benign from malignant lymph nodes, and thus resulting in the relatively low accuracy in N-staging (60). The addition of the metabolic information of PET imaging has been shown to significantly improve the diagnostic accuracy of N-staging compared with that of CT (74). As MR imaging also relies on the morphologic criteria, similar to those of CT, for the assessment of lymph-node metastasis, the simple combination of PET and MR imaging is not expected to have advantages over PET/CT for N-staging (1, 5, 17). Another problem of N-staging is the detection of microscopic metastasis in lymph nodes, as the spatial resolution of PET imaging is limited for detecting it and lymph nodes with micrometastasis often have a morphologically normal shape and size without significant FDG uptake. To date, there are only a few clinical reports regarding the diagnostic performance of MR/PET in N-staging. Recently, Kohan et al. (75) performed a study in 11 patients with lung cancer in order to evaluate the performance of sequential MR/PET for detecting lymph-node metastasis. They reported that the overall interobserver agreement was high (κ = 0.86) for PET/CT and substantial (κ = 0.70) for MR/PET, although the diagnostic accuracy of MR/PET (0.77) for N-staging was slightly less than that of PET/CT (0.80), although the difference was not statistically significant. Considering the previous studies evaluating the additional values of STIR and DWI in the N-staging of lung cancer patients, further studies using multiparametric MRI sequences should be performed in order to improve the diagnostic performance of MR/PET in the detection of metastasized lymph nodes (Fig. 5). The additional use of an MR contrast agent specific for the reticuloendothelial system, such as ultra-small iron oxide particles (USPIO), or a new radiotracer will need to be considered in future research studies (1, 5, 76). Thorek et al. (76) presented a multimodal nanoparticle, 89Zr-ferumoxytol, for the enhanced detection of lymph nodes (LNs) using MR/PET in preclinical disease models. Their work showed that MR/PET could be successfully used to localize the axillary and prostate draining lymphatics using radiolabeled nanoparticles.


Integrated whole body MR/PET: where are we?

Yoo HJ, Lee JS, Lee JM - Korean J Radiol (2015)

66-year-old man with 3.7-cm lung mass (not shown) in right lower lobe.A. Axial, post-contrast, three-dimensional volumetric interpolated breath-hold examination image showed two small right interlobar lymph nodes (arrows). B. Axial fused FDG-MR/PET image showed increased FDG uptake in interlobar nodes (SUVmax: 4.4 and 3.8). Axial, DWI (b = 400) (C) and ADC map showed diffusion restriction in two lymph nodes (D). Concordant findings of right interlobar lymph nodes on ADC map and on fused MR/PET image increased our confidence in reporting right interlobar lymph-node metastasis, and pathology results confirmed right interlobar lymph-node metastasis. ADC = apparent diffusion coefficient, DWI = diffusion-weighted image, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296276&req=5

Figure 5: 66-year-old man with 3.7-cm lung mass (not shown) in right lower lobe.A. Axial, post-contrast, three-dimensional volumetric interpolated breath-hold examination image showed two small right interlobar lymph nodes (arrows). B. Axial fused FDG-MR/PET image showed increased FDG uptake in interlobar nodes (SUVmax: 4.4 and 3.8). Axial, DWI (b = 400) (C) and ADC map showed diffusion restriction in two lymph nodes (D). Concordant findings of right interlobar lymph nodes on ADC map and on fused MR/PET image increased our confidence in reporting right interlobar lymph-node metastasis, and pathology results confirmed right interlobar lymph-node metastasis. ADC = apparent diffusion coefficient, DWI = diffusion-weighted image, FDG = fluorodeoxyglucose, MR/PET = magnetic resonance imaging/positron emission tomography, SUVmax = maximum standardized uptake value
Mentions: For the evaluation of locoregional lymph-node metastasis, cross-sectional imaging modalities, including CT and MR imaging, are dependent mainly on the size and shape of lymph nodes in order to differentiate benign from malignant lymph nodes, and thus resulting in the relatively low accuracy in N-staging (60). The addition of the metabolic information of PET imaging has been shown to significantly improve the diagnostic accuracy of N-staging compared with that of CT (74). As MR imaging also relies on the morphologic criteria, similar to those of CT, for the assessment of lymph-node metastasis, the simple combination of PET and MR imaging is not expected to have advantages over PET/CT for N-staging (1, 5, 17). Another problem of N-staging is the detection of microscopic metastasis in lymph nodes, as the spatial resolution of PET imaging is limited for detecting it and lymph nodes with micrometastasis often have a morphologically normal shape and size without significant FDG uptake. To date, there are only a few clinical reports regarding the diagnostic performance of MR/PET in N-staging. Recently, Kohan et al. (75) performed a study in 11 patients with lung cancer in order to evaluate the performance of sequential MR/PET for detecting lymph-node metastasis. They reported that the overall interobserver agreement was high (κ = 0.86) for PET/CT and substantial (κ = 0.70) for MR/PET, although the diagnostic accuracy of MR/PET (0.77) for N-staging was slightly less than that of PET/CT (0.80), although the difference was not statistically significant. Considering the previous studies evaluating the additional values of STIR and DWI in the N-staging of lung cancer patients, further studies using multiparametric MRI sequences should be performed in order to improve the diagnostic performance of MR/PET in the detection of metastasized lymph nodes (Fig. 5). The additional use of an MR contrast agent specific for the reticuloendothelial system, such as ultra-small iron oxide particles (USPIO), or a new radiotracer will need to be considered in future research studies (1, 5, 76). Thorek et al. (76) presented a multimodal nanoparticle, 89Zr-ferumoxytol, for the enhanced detection of lymph nodes (LNs) using MR/PET in preclinical disease models. Their work showed that MR/PET could be successfully used to localize the axillary and prostate draining lymphatics using radiolabeled nanoparticles.

Bottom Line: This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions.Various early clinical applications of integrated MR/PET are also addressed.Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology, Seoul National University Hospital, Seoul 110-744, Korea.

ABSTRACT
Whole body integrated magnetic resonance imaging (MR)/positron emission tomography (PET) imaging systems have recently become available for clinical use and are currently being used to explore whether the combined anatomic and functional capabilities of MR imaging and the metabolic information of PET provide new insight into disease phenotypes and biology, and provide a better assessment of oncologic diseases at a lower radiation dose than a CT. This review provides an overview of the technical background of combined MR/PET systems, a discussion of the potential advantages and technical challenges of hybrid MR/PET instrumentation, as well as collection of possible solutions. Various early clinical applications of integrated MR/PET are also addressed. Finally, the workflow issues of integrated MR/PET, including maximizing diagnostic information while minimizing acquisition time are discussed.

Show MeSH
Related in: MedlinePlus