A novel stereotactic frame for real PET-guided biopsies: A preclinical proof-of-concept.

PURPOSE: To design, build and test a stereotactic device that allows PET image-guided biopsies to be performed. METHODS: An initial prototype consisting of four main pieces, one of which contains radioactive markers to make it visible in the PET images, was built using a 3D printer. Once the device is mounted, a spherical coordinate system is built with the entrance needle point in the skin as the origin of coordinates. Two in-house software programs, namely getCoord.ijm, which obtains the spherical coordinates of the tumour tissue to be biopsied, and getNeedle.ijm, which virtualizes the inner needle tip once the puncture has taken place, were written. This prototype was tested on an FDG-doped phantom to characterize both the accuracy of the system and the procedure time. RESULTS: Up to 11 complete biopsy procedures were conducted. The mean total procedure time was less than 20min, which is less than the procedure time of conventional standard CT-guided biopsies. The overall accuracy of the system was found to be 5.0±1.3mm, which outperforms the criterion used in routine clinical practice when targeting tumours with a diameter of 10mm. CONCLUSIONS: A stereotactic frame to conduct real PET image-guided biopsies has been designed and built. A proof-of-concept was performed to characterize the system. The procedure time and accuracy of the system were found to meet the current needs of physicians performing biopsies.

Identification of low variability textural features for heterogeneity quantification of 18F-FDG PET/CT imaging.

OBJECTIVE: To identify those textural features that are insensitive to both technical and biological factors in order to standardise heterogeneity studies on 18F-FDG PET imaging. MATERIALS AND METHODS: Two different studies were performed. First, nineteen series from a cylindrical phantom filled with different 18F-FDG activity concentration were acquired and reconstructed using three different protocols. Seventy-two texture features were calculated inside a circular region of interest. The variability of each feature was obtained. Second, the data for 15 patients showing non-pathological liver were acquired. Anatomical and physiological features such as patient's weight, height, body mass index, metabolic active volume, blood glucose level, SUV and SUV standard deviation were also recorded. A liver covering region of interest was delineated and low variability textural features calculated in each patient. Finally, a multivariate Spearman's correlation analysis between biological factors and texture features was performed. RESULTS: Only eight texture features analysed show small variability (<5%) with activity concentration and reconstruction protocol making them suitable for heterogeneity quantification. On the other hand, there is a high statistically significant correlation between MAV and entropy (P<0.05). Entropy feature is, indeed, correlated (P<0.05) with all patient parameters, except body mass index. CONCLUSIONS: The textural features that are correlated with neither technical nor biological factors are run percentage, short-zone emphasis and intensity, making them suitable for quantifying functional changes or classifying patients. Other textural features are correlated with technical and biological factors and are, therefore, a source of errors if used for this purpose.