Tumor measurements: CT

The CT images were acquired following completion of the US examination. The dog was placed in ventral recumbency on the CT (GE Light Speed, 8-detector, Milwaukee, WI) table. Scout images were acquired. Helical images with a slice thickness of 1.25 mm and pitch of 1.35 were acquired from the diaphragm through the perineum. The tube rotation was 0.8 seconds with a fluctuating mA that had a maximum of 400 and a set kVp of 120. The field of view was 500 mm with a matrix of 512 × 512.

Three separate series were acquired and are as follows: (1) empty urinary bladder; (2) infusion of 2 ml/kg of 0.9% sterile saline into the urinary bladder; (3) following a hand injection of intravenous administration of 2 mL/kg of iohexol 240 (Omnipaque, GE Healthcare, Princeton, NJ 08540) via a cephalic vein catheter within the urinary bladder distended as in series 2. Transverse images were then reconstructed into sagittal and dorsal plane images for both bone and standard algorithms; however, the standard algorithm with a window width of 400 and window level of 40 was used for review. The tumor volumes were measured on the pre-contrast and post-contrast series that had infused 2 mL/kg saline (Figure 2).

Transverse images of a urinary bladder transitional cell carcinoma along the dorsal margin of the urinary bladder. Figure 2A demonstrates computed tomography (CT) linear measurements with the maximum width and height of the tumor. Figure 2B shows the CT tracing of the tumor. Figure 2C is a transverse image of the same tumor on ultrasound. The right side of the patient is to the left of the image indicated by an ‘R’.

Linear measurements were made on post-contrast CT images. The dorsal plane images were initially reviewed to evaluate the position of the urinary bladder relative to the sagittal plane (long axis) of the patient. If the urinary bladder was parallel to the sagittal plane of the patient, the maximum length of the tumor was measured using dorsal or sagittal plane images. The maximum width of the tumor was measured using dorsal or transverse plane images. The maximum height of the tumor was measured using sagittal or transverse plane images. Measurements were made using a DICOM viewer (eFilm Workstation 3.2, Merge Healthcare, Chicago, IL 60654). If the sagittal plane of the urinary bladder was not parallel to the sagittal plane of the patient, orthogonal multi-planar reformats of the urinary bladder were made using the DICOM viewer using the sagittal plane of the urinary bladder as a point of reference. Length, width and height measurements were of the tumor were made using the multi-planar reformatted images to the nearest tenth of a millimeter. Two observers (ETH, WTD) independently made measurements of each tumor at each time point.

Tumor volume tracing measurements were made using a commercial DICOM viewer (Horos2k v. 2.0.2, https://www.horosproject.org). The tumor volumes were measured on the pre-contrast and post-contrast series that had infused 2 mL/kg saline. Two observers (AJL, ETH) independently evaluated each transverse slice and traced the outline of the tumor with the pencil tool on each slice in which a portion of the transitional cell carcinoma tumor was present. In the cases in which multiple non-contiguous pieces of a tumor were present on a single transverse slice, each individual piece of the tumor was traced with the pencil tool and their areas were added together. For tracing purposes, the assumption was made that the transitional cell carcinoma tumors had infiltrated the urinary bladder wall to the level of the serosal. Observer A was a fourth-year veterinary student (AJL) and observer B was a board-certified veterinary radiologist (ETH). The tumor area (mm²) on each CT slice was multiplied by the slice thickness (1.25 mm) to yield a volume for each individual transverse slice (mm³). The volume of the tumor from each CT slice was then added together to yield a total tumor volume (mm³). This process was applied to both pre-contrast and post-contrast images from each dog obtained on week 0, week 8, and week 16. To help minimize bias, each observer measured the images in the following systematic format: week 0 pre-contrast, week 8 pre-contrast, week 16 pre-contrast, week 0 post-contrast, week 8 post-contrast, week 16 post-contrast. After a temporal recess (a minimum of 30 days), measurements were repeated utilizing this same method.