Histology and ultrasound fusion of excised prostate tissue using surface registration

We present a method for combining histological data with 3D ultrasound of excised prostate tissue using surface registration. With this technique, 3D prostate cancer lesions can be properly located and visualized within a B-scan volume for tissue characterization comparisons. Three prostate specimens were scanned with a GE Logiq 700 (Expert series) to obtain 2D B-scan sequences. The prostate boundaries were manually segmented from each sequence and reconstructed into 3D volumes. Specimens were fixed, sectioned into slabs, then mounted whole onto slides. Cancerous lesions were outlined by a pathologist. The slides were photographed with an Optronics Spot digital camera using Image-Pro Plus software on a PC. The gland surface was manually segmented from 2D histology images and reconstructed into a volume. Various reconstruction problems were addressed, such as specimen shrinkage due to the fixing and staining processes. The fusion algorithm translates and rotates one surface volume in 3D to find the best surface overlap. The resulting geometric transform is used to reorient the original image volume. The displacement error was determined by measuring the urethra offsets in final volume cross-sections. The offset distance ranged from 1.25 mm to 3.45 mm with an average of 2.36 mm. Another measure to gauge volume alignment is to calculate the ratio of overlapping voxels to total combined voxels(intersection/union). For a perfect case, this ratio will be 1. The ratios for the three cases ranged in value from 0.774 to 0.845.