Evaluation of the tumor registration error in biopsy procedures performed under real-time PET/CT guidance

Abstract

Purpose: The purpose of this study is to quantify tumor displacement during real-time PET/CT guided biopsy and to investigate correlations between tumor displacement and false-negative results.

Methods: 19 patients who underwent real-time ¹⁸ F-FDG PET-guided biopsy and were found positive for malignancy were included in this study under IRB approval. PET/CT images were acquired for all patients within minutes prior to biopsy to visualize the FDG-avid region and plan the needle insertion. The biopsy needle was inserted and a post-insertion CT scan was acquired. The two CT scans acquired before and after needle insertion were registered using a deformable image registration (DIR) algorithm. The DIR deformation vector field (DVF) was used to calculate the mean displacement between the pre-insertion and post-insertion CT scans for a region around the tip of the biopsy needle. For 12 patients one biopsy core from each was tracked during histopathological testing to investigate correlations of the mean displacement between the two CT scans and false-negative or true-positive biopsy results. For 11 patients, two PET scans were acquired; one at the beginning of the procedure, pre-needle insertion, and an additional one with the needle in place. The pre-insertion PET scan was corrected for intraprocedural motion by applying the DVF. The corrected PET was compared with the post-needle insertion PET to validate the correction method.

Results: The mean displacement of tissue around the needle between the pre-biopsy CT and the postneedle insertion CT was 5.1 mm (min = 1.1 mm, max = 10.9 mm and SD = 3.0 mm). For mean displacements larger than 7.2 mm, the biopsy cores gave false-negative results. Correcting pre-biopsy PET using the DVF improved the PET/CT registration in 8 of 11 cases.

Conclusions: The DVF obtained from DIR of the CT scans can be used for evaluation and correction of the error in needle placement with respect to the FDG-avid area. Misregistration between the pre-biopsy PET and the CT acquired with the needle in place was shown to correlate with false negative biopsy results.

Keywords: PET/CT; biopsy; image registration; image-guidance; oncology.

Figure 1

Clinical Workflow of a real‐time PET/CT guided biopsy without (a) and with a second PET scan (b). Images from Patient 12 are shown for illustration. In part (a) is shown the workflow when only one PET scan is performed right before needle insertion and in part (b) is explained the workflow when an additional PET scan is acquired after needle insertion. In both cases an initial PET/CT (PET_pre/CT_pre) was acquired and fused to plan the needle insertion. Once the needle was inserted; in case (a) an additional CT was acquired (CT_needle) and fused with the initial PET_pre or in case (b) a CT plus and additional PET were acquired and fused (CT_needle/PET_needle). [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

Displacement vector field displayed on top of a transverse CT_needle image. The black rectangle defines the ROI around the needle, inside which the mean displacement was calculated. For reference the needle notch (thin part near needle end) is 2 cm long. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

The Fuzzy locally adaptive Bayesian (FLAB) segmentation contours obtained for PET_pre, PET_needle, and PET_corrected are displayed in green, red, and blue, respectively, on top of the fused (a) CT_needle/PET_pre; (b) CT_needle/PET_needle; (c) CT_needle/PET_corrected; (d) The three PET segmentation contours are displayed on top of the CT_needle image (zoomed). The distance d between the middle of the notch of the needle (seen as voxels in white color on the CT_needle image) and the center of mass of the PET_needle segmentation contour is shown for illustration. These scans were obtained from patient 12. [Color figure can be viewed at wileyonlinelibrary.com]

Figure 4

(a) The distance between the biopsy needle seen in the CT_needle and the center of mass of the segmentation contour of PET_needle is compared to the same distance as obtained for PET_pre, and PET_corrected. The plot shows that the corrected PET image is closer to the PET image with the needle for most cases. (b) Illustration of how the distance d between the needle notch and the PET segmentation contour center of mass is measured. The segmentation contours in the different images are illustrated by different color circles. [Color figure can be viewed at wileyonlinelibrary.com]