The benefits of PET – MRI in oncological staging

After a tumor is diagnosed, in order to plan the accurate treatment and predict survival, local and whole-body staging should be performed.

MRI is the most superior imaging method in local staging (T). Since the resolution is increased with 3-Tesla examination, the local staging of rectal cancer, gynecologic tumors, head and neck tumors, and hepatobiliary neoplasms are performed in detail.

Even though Lymph nodes (N) can be assessed in terms of size with MRI, PET examination is required to detect which lymph nodes contain tumor deposits. Lymph nodes containing tumor cells despite of their normal size are also detected with PET agents. The patient undergoes a PET scan for the detection of distant metastases (M).

Since FDG uptake can be limited in localizations such as the central nervous system, liver, bone marrow and in tumor types such as mucinous neoplasms and RCC in PET, the patient should also be scanned for cerebral, upper abdominal, and spinal pathologies in MRI.

For an accurate TNM staging, the patient has to undergo both MRI and PET scan multiple times. This is a troublesome and expensive process.

With PET-MRI, local staging is performed very precisely; Lymph nodes and distant metastases are displayed as a whole simultaneously, complementing each other in the regions where both examinations are powerful and no additional examination is required.

With the rapid evaluation of response to treatment;

• In cases that are unresponsive to treatment, change of therapy makes a positive contribution to the course of the disease.
• With the earlier evidence of therapy response or failure, treatment becomes more cost-effective
• Response to treatment cannot be evaluated only in terms of the change observed in the size of the tumor alone.

With a functional MRI examination, tumor perfusion (antiangiogenic treatment response), density and metabolism of tumor cells (Diffusion MRI, MR Spectroscopy) and with PET scan, the metabolic response of the tumor and viability of tumor cells are evaluated in the earliest time frame.

PET – MRI ensures the earliest and most accurate assessment of treatment response by simultaneously displaying both the changes in functional MRI and the uptake of PET tracers. This enables an accurate and rapid focus on the treatment plan of patients.

The PET – MRI combination plays an important role in the imaging of padiatric patients and adolescents who can potentially be healed. The effective dose in a PET – MRI scan is only 20% of that of the equivalent PET – CT scan.

Brain Tumors

• Leads to better detection of brain lesions that can be underestimated or missed on a PET/CT.
• Improves diagnostic accuracy and changes the course of surgery and therapy planning.
• Corrects for head motion leading to a significant increase in temporal resolution.
• Differentiates between areas of necrosis and viable tissue after surgery and radiation therapy.

Breast Cancer

Increases specificity and decreases false negatives more than an MRI or FDG PET scan alone.

Improves evaluation of small liver lesions, lymph nodes and bony metastasis because of high soft-tissue contrast of MRI.
Assists in the selection of lesions to biopsy in women who show multiple enhancing lesions on an MR scan.

Cervical Cancer

• Increases diagnostic confidence by providing both the biological behavior and local extent of the tumor in one test.
• Reduces errors in diagnosis and evaluation of treatment response that can be caused by bladder and bowel obstruction.

Colorectal Cancer

• Increases the detection of tumor recurrence and/or newly developed distant metastases.
• Distinguishes between scar tissue and recurrence after treatment or surgery.

Esophageal Cancer

• Improves diagnosis, and all aspects of further evaluation using MRI sequences that are able to define the layers of the esophageal wall.
• Increases assessment of tracheobronchial, aortic and pericardial invasion.

Head & Neck Cancer

• Combines the excellent soft-tissue contrast of MRI and the metabolic evaluation of lymph node tumor presence of PET to improve the diagnosis and treatment of head and neck cancers.
• Eliminates artifacts from dental implants which can obscure tumors in or around the mouth.
• Increases precision of anatomic localization of abnormal masses.

Liver Disease

• Since the liver is one of the most common sites for metastasis of various cancers including lung, breast and colorectal, MRI/PET is a better tool for staging because of it.
• Improves detection of small liver lesions, which can often be too small to characterize on a PET/CT.
• Increases diagnostic confidence in the characterization of liver lesions.
• Differentiates between normal liver tissue and tumor burden.

Lung Cancer

• Improves diagnosis, and all aspects of further evaluation using MRI sequences that are able to define the layers of the esophageal wall.
• Increases assessment of tracheobronchial, aortic, and pericardial invasion.

Lymphoma

MRI/PET plays an important role in all aspects of lymphoma evaluation since it:

• Reduces radiation exposure over a lifetime by eliminating the CT radiation from repetitive PET/CT scans.
• Increases the accuracy of detection through the addition of diffusion-weighted imaging in MRI.
• Improves detection of low-grade or less-FDG avid lymphomas.

Melanoma

Studies have proven that the combination of diffusion-weighted MRI and PET images are a powerful tool to achieve whole-body staging and influence therapeutic approaches in patients with melanoma.

Myeloma

The increased sensitivity of MRI and PET combined can help detect infiltrative bone marrow lesions.

Neuroendocrine Tumors

MRI/PET with FDG as well as with Ga68-DOTATOC has the ability to stage and monitor therapy in patients with neuroendocrine tumors.

Ovarian Cancer

Studies demonstrate the combined strength of MRI and PET in all aspects of gynecological oncological evaluation. In addition, MRI/PET improves the detection of disease in the pelvis.

Pancreatic Cancer

Studies show that MRI/PET is superior to PET/CT in characterizing pancreatic tumors since:

• The CT portion of the PET/CT may have limited visualization of pancreatic tumors.
• T1-weighted images from MRI are superior to CT.

Prostate Cancer

Increases the certainty of localization because of its ability to distinguish between uptakes in the bowel, bladder and ureter.

• Improves assessment of small structures in the pelvis using high-resolution MRI.
• Enhances sensitivity in the detection of bone metastasis; PET and MRI combined have a higher sensitivity in this setting than CT and Nuclear Medicine Bone scans.

Renal Cancer

Primary and secondary lesions in the kidneys can be challenging to identify on PET/CT since FDG uptake can be misinterpreted as a urinary activity. However, when PET is fused with MRI, renal malignancies can be better detected.

Sarcoma

Functional MRI (urography) can further help understand the blockage of the urethra that can be caused by distant metastasis.

In patients with both soft-tissue and bone sarcomas, MRI/PET:

• Increases the diagnostic accuracy for T-staging.
• Improves the assessment of change in tumor volume after therapy.
• Corrects for head motion leading to a significant increase in temporal resolution.
• Differentiates between areas of necrosis and viable tissue after surgery and radiation therapy.
• Simultaneous imaging of MRI and PET has better mapping and fusion image quality than PET and MRI separately.

Testicular Center

MRI/PET provides the benefits of PET and MRI imaging, both known to be strong diagnostic tools in testicular cancer, without the radiation dose of CT from PET/CT.

Thyroid Cancer

MRI/PET combines important structural and functional data useful in staging, surgical planning, radioactive iodine treatment planning and follow-up in different types of thyroid cancer.

• Whole-body Tumor Diagnosis with low radiation
• Displaying mucinous tumors, prostate cancer, RCC, HCC and bronchoalveolar cancer in a single examination
• Displaying liver, brain, spinal cord and bone tumors and their metastases in one session.
• Ensuring whole – body TNM staging in one session
• Target-oriented tumor diagnosis with cell-specific functional MRI imaging methods and tumor-specific PET agents.
• More rapid evaluation of the response to new generation therapies
• Safe use with low radiation in pediatric oncology cases