Barbara Lewellen

FDG-PET/CT–guided intensity modulated head and neck radiotherapy: A pilot investigation†‡

2‐deoxy‐2[18F]fluoro‐d‐glucose–positron emission tomography (FDG‐PET) imaging can be registered with CT images and can potentially improve neck staging sensitivity and specificity in patients with head and neck squamous cell cancer. The intent of this study was to examine the use of registered FDG‐PET/CT imaging to guide head and neck intensity modulated radiotherapy (IMRT) planning.

Magnetically Targeted Viral Envelopes: A PET Investigation of Initial Biodistribution

Gene and drug therapy for organ-specific diseases in part depends on the efficient delivery to a particular region of the body. We examined the biodistribution of a viral envelope commonly used as a nanoscale gene delivery vehicle using positron emission tomography (PET) and investigated the magnetic alteration of its biodistribution. Iron oxide nanoparticles and 18F-fluoride were encapsulated by hemagglutinating virus of Japan envelopes (HVJ-Es). HVJ-Es were then injected intravenously in the rat and imaged dynamically using high-resolution PET. Control subjects received injections of encapsulated materials alone. For magnetic targeting, permanent magnets were fixed on the head during the scan. Based on the quantitative analysis of PET images, HVJ-Es accumulated in the liver and spleen and activity remained higher than control subjects for 2 h. Histological sections of the liver confirmed imaging findings. Pixel-wise activity patterns on coregistered PET images of the head showed a significantly different pattern for the subjects receiving magnetic targeting as compared to all control groups. Imaging demonstrated the initial biodistribution of a viral envelope within the rodent by providing quantitative behavior over time and in specific anatomical regions. Magnetic force altered the biodistribution of the viral envelope to a target structure, and could enable region-specific delivery of therapeutic vehicles noninvasively.

IC-102-02

Background: CMS approval of FDG PET to differentiate AD from FTD raises diagnostic challenges as patients are increasingly referred to PET centers from clinical settings. Objectives: To characterize cortical metabolic features of clinically referred patients. Methods: Fifteen patients (11 women, mean age 69 /-11 years) with mild to moderate dementia (mean MMSE 23 /6) clinically consistent with both AD and FTD underwent FDG PET in 3D data acquisition mode after a transmission scan for attenuation correction. Reconstructed images were transformed to standard stereotactic coordinates, extracting gray matter activity using 3D stereotactic surface projections. Individual patient data were compared to those of 30 cognitively normal elderly volunteers using pixel-by-pixel Z-score mapping to identify hypometabolic patterns (AD, parietotemporal and posterior cingulate; FTD, frontotemporal; and NS, non-specific, neither AD or FTD). Structural MR images were compared to identify metabolic changes of presumed ischemic origin. Results: Eleven of 15 patients exhibited a pattern consistent with one of the neurodegenerative diagnoses being considered (8, or 53%, AD pattern; 3, or 20%, FTD pattern) and 4 exhibited an NS pattern. Among the 11 patients with a distinct neurodegenerative pattern, focal or watershed hypometabolism consistent with ischemia was found in 2/8 with AD pattern and 1/3 with FTD pattern, and significant hemispheric asymmetry (Z-score difference 2) was found in 4 patients (2 each with AD and FTD patterns). Temporal hypometabolism was more severe than frontal in 1 of the 3 patients with an FTD pattern, and none of the FTD patients showed the classic ‘lobar’ frontal hypometabolism. Conclusions: Patients clinically referred for FDG PET to help differentiate between AD and FTD exhibit significant cortical metabolic heterogeneity. Sources of heterogeneity identified in this study include hemispheric asymmetry, concurrent ischemic changes corroborated by MR, and regional variability within FTD that most likely reflects variations inherent in its pathology. A significant minority of patients meeting clinical diagnostic criteria may not be classifiable by FDG PET as having either AD or FTD. Further investigation of this heterogeneity is required to support optimal clinical interpretation of imaging findings. (NIH R01 NS045254, NIA P50 AG 05136).

Comparing the effects of standard and segmented attenuation correction

We have evaluated a segmentation algorithm developed by General Electric for the Advance positron emission scanner (PET). Phantom studies were performed to measure the accuracy in emission scans reconstructed with segmented, attenuation data as a function of transmission scan time. The results indicated errors of less than 2% will be made in emission scan data reconstructed with transmission scan times of 3 minutes. Based on the phantom results, 185 patient data sets were acquired with both long (15 min.) non-segmented and short (3 min.) segmented attenuation scans. Comparisons of scan data in foci of abnormal uptake yielded a correlation coefficient between long and short scan SUV maximum values of 0.99 and a mean absolute difference of 4.6%. The average SUV values in lung between long and short has a correlation coefficient of 0.99 and a mean absolute difference of 3.1%. The corresponding values from the liver had a correlation coefficient of 0.96 and mean absolute difference of 7.4%. Visual review by physicians noted minor differences, but when grading the images on a scale of 1 to 5, 91% of the time there was no difference. In all cases comparing the long and short attenuation and no abnormal sites were missed.