Research shows how MRI and PET/CT can work together in cancer assessment

Preliminary studies presented Tuesday gave radiologists a glimpse of future imaging practices for cancer patients: a molecular nuclear imaging test to assess the extent of hypoxia and functional MRI to monitor the response of head and neck carcinoma to treatment.

Dr. Amita Shukla-Dave of Memorial Sloan-Kettering Cancer Center established that dynamic contrast-enhanced MRI and F-18 misonidazole (MISO) PET/CT can work together to evaluate the perfusion and hypoxic status of squamous cell carcinoma of the head and neck.

Nine HNSCC patients with nodal metastasis were assessed on a 1.5T scanner before receiving chemo- and radiation therapy. They were administered a 0.1 mmol/kg bolus of gadolinium. Dynamic perfusion images were acquired on the nodes using a fast multiphase spoiled gradient echo sequence.

For the PET/CT hypoxia study, F-18 MISO was injected two hours before imaging. After standard reconstruction, images were transmitted to a workstation for interpretation. Uptake was scored on a three-point scale (mild, moderate, and severe) based on visual analysis.

Comparisons of images from the two modalities established an inverse relationship between hypoxia and perfusion. Hypoxic nodes tended to be poorly perfused, and nodes with no hypoxia were well-perfused, according to Shukla-Dave.

In a separate study of 16 patients, Dr. Sungheon Kim, from Dr. Jerry Glickson's lab at the University of Pennsylvania, evaluated various functional MRI measures, including apparent diffusion coefficient mapping, for monitoring the early response of squamous cell head and neck tumors to chemo- and radiation therapy

Kim performed T2-weighted imaging on a 1.5T scanner equipped with a neck array coil to locate the tumor, then acquired eight axial slices with a field-of-view of 26 cm and slice thicknesses of 5 mm to cover the tumor. Diffusion-weighted imaging involved a PGSE/EPI sequence with four b-values: 0, 500, 1000, and 1500 s/mm2. Scans were performed before treatment, one week after the initiation of treatment, and after its completion. Corresponding T1- and T2-weighted imaging confirmed that tumor volume changes do not measure early treatment response, Kim said. Anatomic imaging established which patients experienced a complete response (75% tumor shrinkage) or partial/no response (less than 75% tumor shrinkage) after the completion of therapy.

The partial/no response group appeared to have longer T1 and T2 times and lower K^trans measures of diffusion than the complete-response group, but the differences were not statistically significant. No differences in ADC changes were observed between the two groups, Kim said.

For the complete responders, the measures did not change predictably from time point to time point. They increased initially, but then decreased, while the values for the partial/no response group either increased or decreased steadily over time. Tumor heterogeneity posed measurement problems.

Additional trials involving more patients are needed to find a reliable biomarker to predict treatment response, Kim said.

For related news, examine the following from the Diagnostic Imaging archives:

Head and neck reports must combine accurate descriptions with foresight

CT and MR imaging assist nasopharyngeal tumor mapping

64-slice experience bolsters head and necks expertise