PET/MRI

• The PET/MRI study plays an important role in epilepsy cases:

• 16 years old patient with long standing epileptic attacks, on anti-epileptic treatment with visual function:

(A) Mild left cerebral hemi-atrophy evidenced by mild prominence of CSF spaces in the left side including cortical sulci as well as the left lateral ventricle compared to the right side. The cortex in generally is reduced compared to the contra-lateral more normal right side.

(B&C) After super-imposition of the PET data on the conventional MRI data there appears to be hypo-metabolic status with reduced uptake of the 18f-FDG tracer within the left cerebral hemisphere cortical regions.

• The PET/MRI study plays an important role in brain tumor cases:

• 70 years old patient with pathologically proven right frontal region high-grade glioma (glioblastoma WHO grade IV), he underwent surgery and then received radiotherapy.

(A) The right fontal lesion shows heterogeneous signal on all images due to the multi-component of hemorrhagic components and solid enhancing parts around a non-enhancing cavity.

(B&C) The PET/MR data shows an evident hyper-metabolic status along the inner part of the post operative and therapy cavity, and this is due to more avid uptake of the FDG tracer by the suggested viable tumor tissue medially compared to the lesser uptake by normal brain parenchyma specially the white matter.

• The PET/MRI study plays an important role in dementia cases

• Old patient with amnesia:

(A) Axial FLAIR reveals prominent ventricles and sulci spaces & cerebral atrophy.

(B &C) Axial fused PET MRI reveals bilateral fronto-temporal and parietal hypo-metabolism. 

It is a PET/MRI examination that incorporates MRI and PET imaging form skull to legs after intravenous injection of the radioactive material Gallium PSMA which detect cancer prostate cells, in the prostate and its metastasis all over the body.

• Better TNM staging: PET MR is considered now a revolution in imaging as despite the PET/CT can provide NM staging but it cannot offer local staging as the MR can do due to magnificent better spatial resolution and great soft tissue details.
• Shorter study time: For patients with prostatic cancer the multi-parametric MRI study is needed to detect the tumor and its local staging as well as the PET/CT study to detect the metastatic spread of the tumor as presence of metastasis prevents surgery so both studies (PET/CT and MRI multiparametric) are needed, now with PET/MRI this can be done in one study only saving time, effort and cost.
• PET/MRI is also of high advantage than the traditional PET imaging  as there is no radiation dose and  also has a higher ability to detect even faint uptake of the tracer.

PSMA PET/MR Is more sensitive showing the focal uptake of left iliac bone, left pelvic lymph nodes as well as the tiny right pelvic lymph node.

Patient 66 years old with history of prostate cancer submitted for 68Ga-PSMA PET study that showing a well localized uptake of the tracer which 2 weeks later appeared in the CT study.

Liver metastasis in segment IVa

A small lesion difficult to characterized but in PET/MRI:

The lesion shows slightly elevated tracer uptake (SUV 3.4), ring enhancement in T1 post contrast and diffusion restriction in DWI, which are signs of malignancy.

T2 coronal MRI image shows a large right colon mass with multiple low signal intensity lymph nodes (left).

PET-MRI coronal fusion images better reveal the colon mass and chain of mesenteric lymph nodes that extends to the paracaval region (middle).

PET 3D image shows the prominent FDG activity in the colon cancer and lymph node metastases (right).

MR/PET of a patient with rectal cancer which was performed on a sequential MR/PET system.

Asymmetrical thickening of the rectal wall is seen in the axial (a), sagittal (b), and coronal (c) planes of the T2 TSE sequence.

Associated increased FDG uptake in relationship to the finding described previously is seen in the PET acquisition (d-f).

Fusion images (g-i) help determine to malignant origin of the thickening and the absence of involved lymph nodes.

62 year-old male for initial staging of pancreatic adenocarcinoma. 

The PET-MRI axial fusion image shows a large hypermetabolic mass in the body of the pancreas (top left).

The T1 axial image demonstrates a mass in the pancreatic body that is isointense to the normal pancreatic tissue (top right).

The T2 axial images show considerable main pancreatic duct dilatation (bottom left).

The PET axial image displays intense metabolic activity within the pancreatic tumor relative to the liver activity with standardized uptake value of 8.7

• PET/MRI of the breast and whole-body can bring metabolic, anatomic, spectroscopic, diffusion and perfusion-based data together in a single examination.
• The multiparametric imaging offered by PET/MRI provide new biomarkers, aiming  at personalizing treatment and providing more  prognostic information.
• Breast PET/MRI has shown promise in reducing unnecessary biopsies that would be recommended based on their current standard DCE-MRI.
• Breast PET/MRI is more important before and during neoadjuvant therapy, where lend increased precision to breast cancer treatments.
• In local staging, PET/MRI may eventually preclude the need for axillary lymph node tissue sampling.
• In need of whole-body staging or post treatment surveillance, PET/MRI has the benefit of lower radiation dose.
• Combining PET and DWI may be important as PET has been shown to  greatly improve the specificity of DWI in whole-body imaging.
• In whole-body imaging for breast cancer, PET/MRI imaging provide higher sensitivity particularly for breast cancers, liver and bone metastases and also brain metastas.

48-y-old woman with history of left breast cancer metastatic to lung and bone obtained to monitor response during chemotherapy.

T1W MR/PET images and contrast enhanced T1W(A,B)  show left breast cancer and several lung metastasis (white arrow) and bony metastasis (black arrow). CT and PET/CT images (C,D) show these metastasis (white and black arrows). As obvious from the previous example PET/MRI shows the same data as the PET/CT even in bony metastasis.

Case of left breast invasive ductal carcinoma with positive left axillary lymph nodes. Whole-body PET/MRI detected distant metastatic disease in this patient that was not previously diagnosed. An unexpected rib metastasis is seen enhanced on DCE MRI and is FDG-avid on PET.

PET/MRI                                                            PET/CT

Case of history of left breast cancer metastatic to lung and bone obtained to monitor response during chemotherapy. A liver metastasis is seen on the PET/MR images.

Neoplastic Musculoskeletal Disease

• Multiple myeloma

60-year-old man with history of multiple myeloma who underwent chemotherapy and had laboratory evidence of relapse.

(A) whole-body low-dose CT shows subtle area of soft-tissue density in proximal left femoral shaft, (B) without corresponding osteolysis. (C) Subsequent FDG PET/MRI shows T1-hypointense marrow-replacing lesion in same location with increased FDG activity seen on fused PET/MR image (D), consistent with active disease.

CT often fails to detect early focal lesions that are not yet lytic. Owing to high soft tissue contrast and better ability to detect marrow lesions, whole body MRI has also been used for the evaluation of multiple myeloma

• Rhabdomyosarcoma

A 13-year-old girl with neurological symptoms and pain in the right knee.

(A) PET MIP demonstrates widespread foci of FDG-accumulation suspected for  disseminated malignancy. (B–D) Coronal MRI T2 fat sat, FDG-PET, and fused PET-MR show soft tissue and BM lesions.

• Peripheral Nerve Sheath Tumor

61-year-old female with a large pelvic mass discovered on CT and non-diagnostic biopsies taken during laparoscopic exploration.

(A) T₂-weighted fat-saturated (FS) (B) FS  post-gadolinium spoiled gradient recalled (SPGR) demonstrate a large heterogeneously T₂-hyperintense pelvic mass extending through the right sciatic notch with peri-lesional edema and extensive central necrosis. Corresponding fused T2-weighted FS. (B)  FS  post-gadolinium SPGR  FDG PET-MRI (D) images demonstrate intense peripheral FDG activity. An FDG-avid area was targeted during subsequent CT-guided biopsy, with pathology showing a high-grade malignant peripheral nerve sheath tumor

Non-Neoplastic Musculoskeletal Disease\

• Stress fracture

CT show sclerotic lesions in the dorsal calcaneus and degenerative changes in talonavicular  region but no signs of acute stress fractures. On MRI, a fracture line in the dorsal calcaneus due to an older stress fracture that corresponds to elevated ¹⁸F-NaF PET uptake & Additionally, another stress fracture is shown on PET-MRI in the mediodorsal parts of the cuboid with elevated uptake on ¹⁸F NaF PET .

• Rheumatoid arthritis

MRI provides high-resolution anatomical images to assess structural changes for diagnosis and staging of RA disease. Hybrid PET-MRI systems offer to combine high-resolution morphologic images with early molecular markers to enhance the study of RA.

Hand in early RA acquired on  an integrated PET-MRI system, The highest uptake is seen at the palmer portion of the second metacarpophalangeal joint which  corresponds to synovial thickening and contrast enhancement on MRI.

Neoplastic Musculoskeletal Disease

• Multiple myeloma

60-year-old man with history of multiple myeloma who underwent chemotherapy and had laboratory evidence of relapse.

(A) whole-body low-dose CT shows subtle area of soft-tissue density in proximal left femoral shaft, (B) without corresponding osteolysis. (C) Subsequent FDG PET/MRI shows T1-hypointense marrow-replacing lesion in same location with increased FDG activity seen on fused PET/MRI image (D), consistent with active disease.

CT often fails to detect early focal lesions that are not yet lytic. Owing to high soft tissue contrast and better ability to detect marrow lesions, whole body MRI has also been used for the evaluation of multiple myeloma

• Rhabdomyosarcoma

A 13-year-old girl with neurological symptoms and pain in the right knee.

(A) PET MIP demonstrates widespread foci of FDG-accumulation suspected for  disseminated malignancy. (B–D) Coronal MRI T2 fat sat, FDG-PET, and fused PET/MRI show soft tissue and BM lesions.

• Peripheral Nerve Sheath Tumor

61-year-old female with a large pelvic mass discovered on CT and non-diagnostic biopsies taken during laparoscopic exploration.

(A) T₂-weighted fat-saturated (FS) (B) FS  post-gadolinium spoiled gradient recalled (SPGR) demonstrate a large heterogeneously T₂-hyperintense pelvic mass extending through the right sciatic notch with peri-lesional edema and extensive central necrosis. Corresponding fused T2-weighted FS. (B)  FS  post-gadolinium SPGR  FDG PET/MRI (D) images demonstrate intense peripheral FDG activity. An FDG-avid area was targeted during subsequent CT-guided biopsy, with pathology showing a high-grade malignant peripheral nerve sheath tumor.

Non-Neoplastic Musculoskeletal Disease

• Stress fracture

CT show sclerotic lesions in the dorsal calcaneus and degenerative changes in talonavicular  region but no signs of acute stress fractures. On MRI, a fracture line in the dorsal calcaneus due to an older stress fracture that corresponds to elevated ¹⁸F-NaF PET uptake & additionally, another stress fracture is shown on PET-MRI in the mediodorsal parts of the cuboid with elevated uptake on ¹⁸F NaF PET.

• Rheumatoid arthritis

MRI provides high-resolution anatomical images to assess structural changes for diagnosis and staging of RA disease. Hybrid PET/MRI systems offer to combine high-resolution morphologic images with early molecular markers to enhance the study of RA.

Hand in early RA acquired on an integrated PET/MRI system, The highest uptake is seen at the palmer portion of the second metacarpophalangeal joint which  corresponds to synovial thickening and contrast enhancement on MRI.