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Imaging in head and neck squamous cell carcinoma: the potential role of PET/MRI.

Becker M, Zaidi H - Br J Radiol (2014)

Bottom Line: In head and neck oncology, the information provided by positron emission tomography (PET)/CT and MRI is often complementary because both the methods are based on different biophysical foundations.However, combining PET with MRI has proven to be technically and clinically more challenging than initially expected and, as such, research into the potential clinical role of PET/MRI in comparison with PET/CT, diffusion-weighted MRI (DW MRI) or the combination thereof is still ongoing.Feasibility and quantification issues, diagnostic pitfalls and challenges in clinical settings as well as ongoing research and potential future applications are also discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Imaging, Division of Radiology, Geneva University Hospital, Geneva, Switzerland.

ABSTRACT
In head and neck oncology, the information provided by positron emission tomography (PET)/CT and MRI is often complementary because both the methods are based on different biophysical foundations. Therefore, combining diagnostic information from both modalities can provide additional diagnostic gain. Debates about integrated PET/MRI systems have become fashionable during the past few years, since the introduction and wide adoption of software-based multimodality image registration and fusion and the hardware implementation of integrated hybrid PET/MRI systems in pre-clinical and clinical settings. However, combining PET with MRI has proven to be technically and clinically more challenging than initially expected and, as such, research into the potential clinical role of PET/MRI in comparison with PET/CT, diffusion-weighted MRI (DW MRI) or the combination thereof is still ongoing. This review focuses on the clinical applications of PET/MRI in head and neck squamous cell carcinoma (HNSCC). We first discuss current evidence about the use of combined PET/CT and DW MRI, and, then, we explain the rationale and principles of PET/MR image fusion before summarizing the state-of-the-art knowledge regarding the diagnostic performance of PET/MRI in HNSCC. Feasibility and quantification issues, diagnostic pitfalls and challenges in clinical settings as well as ongoing research and potential future applications are also discussed.

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Hybrid positron emission tomography (PET)/MRI obtained for primary staging of advanced laryngeal squamous cell carcinoma. (a) Fused T2 and b 1000 image (colour overlay) illustrate restricted diffusivity in the right Level VI region (arrow), suggesting metastatic lymph nodes. Note geometric distortion of the overlaid b 1000 image in comparison with T2. Position of the spinal cord (long dashed arrow) and T1 nerve roots (arrowheads) on b 1000. Position of the spinal cord on T2 (short dashed arrow). (b) Corresponding fused T2 and PET show hypermetabolic thyroid nodule (arrow) and absent Level VI metastatic nodes. Ultrasonography with fine-needle aspiration cytology and surgery revealed a benign thyroid nodule and absent Level VI metastases, respectively.
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fig2: Hybrid positron emission tomography (PET)/MRI obtained for primary staging of advanced laryngeal squamous cell carcinoma. (a) Fused T2 and b 1000 image (colour overlay) illustrate restricted diffusivity in the right Level VI region (arrow), suggesting metastatic lymph nodes. Note geometric distortion of the overlaid b 1000 image in comparison with T2. Position of the spinal cord (long dashed arrow) and T1 nerve roots (arrowheads) on b 1000. Position of the spinal cord on T2 (short dashed arrow). (b) Corresponding fused T2 and PET show hypermetabolic thyroid nodule (arrow) and absent Level VI metastatic nodes. Ultrasonography with fine-needle aspiration cytology and surgery revealed a benign thyroid nodule and absent Level VI metastases, respectively.

Mentions: Susceptibility artefacts, attenuation correction artefacts and miscoregistration artefacts can hamper the interpretation of head and neck PET/MRI examinations. Susceptibility artefacts occur as the result of microscopic variations in the magnetic field strength near the interfaces of substances with different magnetic susceptibility. Susceptibility artefacts are commonly seen around ferromagnetic objects as contained in dental restorations or osteosynthesis material. Dephasing of spins and frequency shifts in the tissues surrounding the ferromagnetic objects lead to spatial distortion of the surrounding anatomy as well as to bright and dark areas on MRI sequences. These artefacts are more pronounced at high field strength (3 T vs 1.5 T), on gradient echo sequences, with long echo train length and DWI sequences. Although metal-based restoration materials can degrade MR image quality, they have an even stronger influence on CT image quality90 (Figure 1). As suggested by several authors, the observed artefacts are in general larger on CT than on MR images, the size of the artefact mainly depending on the composition of the ferromagnetic material used.90 A distinct problem is geometric distortion in DW MRI sequences caused by B0 susceptibility differences over the areas imaged. Although parallel imaging techniques reduce geometric distortion, a certain amount of distortion cannot be avoided even with newer DW MRI sequences.91 Because of miscoregistration of the k space, the geometric distortion can be particularly well appreciated when b 1000 images are fused with standard morphological sequences.92 In our experience, this diffeomorphic miscoregistration may result in erroneous interpretation of findings unless morphological MRI sequences are carefully analysed (Figure 2).


Imaging in head and neck squamous cell carcinoma: the potential role of PET/MRI.

Becker M, Zaidi H - Br J Radiol (2014)

Hybrid positron emission tomography (PET)/MRI obtained for primary staging of advanced laryngeal squamous cell carcinoma. (a) Fused T2 and b 1000 image (colour overlay) illustrate restricted diffusivity in the right Level VI region (arrow), suggesting metastatic lymph nodes. Note geometric distortion of the overlaid b 1000 image in comparison with T2. Position of the spinal cord (long dashed arrow) and T1 nerve roots (arrowheads) on b 1000. Position of the spinal cord on T2 (short dashed arrow). (b) Corresponding fused T2 and PET show hypermetabolic thyroid nodule (arrow) and absent Level VI metastatic nodes. Ultrasonography with fine-needle aspiration cytology and surgery revealed a benign thyroid nodule and absent Level VI metastases, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4067029&req=5

fig2: Hybrid positron emission tomography (PET)/MRI obtained for primary staging of advanced laryngeal squamous cell carcinoma. (a) Fused T2 and b 1000 image (colour overlay) illustrate restricted diffusivity in the right Level VI region (arrow), suggesting metastatic lymph nodes. Note geometric distortion of the overlaid b 1000 image in comparison with T2. Position of the spinal cord (long dashed arrow) and T1 nerve roots (arrowheads) on b 1000. Position of the spinal cord on T2 (short dashed arrow). (b) Corresponding fused T2 and PET show hypermetabolic thyroid nodule (arrow) and absent Level VI metastatic nodes. Ultrasonography with fine-needle aspiration cytology and surgery revealed a benign thyroid nodule and absent Level VI metastases, respectively.
Mentions: Susceptibility artefacts, attenuation correction artefacts and miscoregistration artefacts can hamper the interpretation of head and neck PET/MRI examinations. Susceptibility artefacts occur as the result of microscopic variations in the magnetic field strength near the interfaces of substances with different magnetic susceptibility. Susceptibility artefacts are commonly seen around ferromagnetic objects as contained in dental restorations or osteosynthesis material. Dephasing of spins and frequency shifts in the tissues surrounding the ferromagnetic objects lead to spatial distortion of the surrounding anatomy as well as to bright and dark areas on MRI sequences. These artefacts are more pronounced at high field strength (3 T vs 1.5 T), on gradient echo sequences, with long echo train length and DWI sequences. Although metal-based restoration materials can degrade MR image quality, they have an even stronger influence on CT image quality90 (Figure 1). As suggested by several authors, the observed artefacts are in general larger on CT than on MR images, the size of the artefact mainly depending on the composition of the ferromagnetic material used.90 A distinct problem is geometric distortion in DW MRI sequences caused by B0 susceptibility differences over the areas imaged. Although parallel imaging techniques reduce geometric distortion, a certain amount of distortion cannot be avoided even with newer DW MRI sequences.91 Because of miscoregistration of the k space, the geometric distortion can be particularly well appreciated when b 1000 images are fused with standard morphological sequences.92 In our experience, this diffeomorphic miscoregistration may result in erroneous interpretation of findings unless morphological MRI sequences are carefully analysed (Figure 2).

Bottom Line: In head and neck oncology, the information provided by positron emission tomography (PET)/CT and MRI is often complementary because both the methods are based on different biophysical foundations.However, combining PET with MRI has proven to be technically and clinically more challenging than initially expected and, as such, research into the potential clinical role of PET/MRI in comparison with PET/CT, diffusion-weighted MRI (DW MRI) or the combination thereof is still ongoing.Feasibility and quantification issues, diagnostic pitfalls and challenges in clinical settings as well as ongoing research and potential future applications are also discussed.

View Article: PubMed Central - PubMed

Affiliation: Department of Imaging, Division of Radiology, Geneva University Hospital, Geneva, Switzerland.

ABSTRACT
In head and neck oncology, the information provided by positron emission tomography (PET)/CT and MRI is often complementary because both the methods are based on different biophysical foundations. Therefore, combining diagnostic information from both modalities can provide additional diagnostic gain. Debates about integrated PET/MRI systems have become fashionable during the past few years, since the introduction and wide adoption of software-based multimodality image registration and fusion and the hardware implementation of integrated hybrid PET/MRI systems in pre-clinical and clinical settings. However, combining PET with MRI has proven to be technically and clinically more challenging than initially expected and, as such, research into the potential clinical role of PET/MRI in comparison with PET/CT, diffusion-weighted MRI (DW MRI) or the combination thereof is still ongoing. This review focuses on the clinical applications of PET/MRI in head and neck squamous cell carcinoma (HNSCC). We first discuss current evidence about the use of combined PET/CT and DW MRI, and, then, we explain the rationale and principles of PET/MR image fusion before summarizing the state-of-the-art knowledge regarding the diagnostic performance of PET/MRI in HNSCC. Feasibility and quantification issues, diagnostic pitfalls and challenges in clinical settings as well as ongoing research and potential future applications are also discussed.

Show MeSH
Related in: MedlinePlus