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OBJECTIVE To evaluate the effect of kernel and window settings on the assessment of small and complicated vasculature in CT angiographic (CTA) images of kidneys, jejunum with mesentery, and tumors in dogs. ANIMALS 20 healthy dogs and 20 dogs with tumors. PROCEDURES Images from CTA performed previously in dogs were reconstructed with 3 different combinations of kernel and window settings (soft kernel with soft tissue window, soft kernel with bone window, and sharp kernel with bone window), and reconstructed images of the left kidney and the jejunum with the mesentery in healthy dogs and tumors in affected dogs were evaluated by reviewers blinded to the settings. RESULTS For images of kidney and jejunum with mesentery, reviewers’ scores for the conspicuity of vascularity in the arterial phase and the differentiation of the organs from the adjacent structures were significantly higher when viewed in bone window (vs soft tissue window) regardless of kernel setting. For images of head and gastrointestinal tumors, reviewers’ scores for differentiation of intratumoral vasculature were higher when viewed in sharp kernel with bone window versus other setting combinations. However, the conspicuity of gastrointestinal, hepatic, or splenic tumoral vessels from the adjacent structures had higher reviewer scores for images in soft kernel with soft tissue window, compared with other setting combinations. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that reconstruction of CTA images with sharp kernel combined with bone window settings might have clinical utility in evaluating and planning treatments for dogs with various tumors; however, additional research is warranted to further identify effects of various kernel and window setting combinations on assessments of small and complicated vasculature in larger and more diverse populations of dogs with and without tumors.

OBJECTIVE To evaluate the effect of contrast medium injection rate on CT-derived renal perfusion estimates obtained with the maximum slope method in healthy small dogs. ANIMALS 6 healthy sexually intact male purpose-bred Beagles. PROCEDURES All dogs underwent CT perfusion analysis 3 times in a crossover design, receiving a different contrast medium injection rate (1.5, 3.0, and 4.5 mL/s) each time, with a 1-week interval between imaging sessions. All CT images were obtained at the level of the left renal hilus. The time to peak aortic enhancement (TPAE) and time to initial renal venous enhancement (TIRVE) were measured from time-attenuation curves. The renal CT perfusion estimates (blood flow and blood volume) were estimated by use of the maximum slope method, which assumes no venous outflow of contrast medium during CT perfusion analysis. RESULTS The TPAE occurred at or before the TIRVE at all injection rates. Median values of estimated blood flow and blood volume did not differ significantly among injection rates. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the assumption of no venous outflow of contrast medium during renal CT perfusion analysis with the maximum slope method was satisfied for all 3 contrast medium injection rates in the evaluated dogs. A low injection rate may be more practical than higher injection rates that require large catheters for CT perfusion analysis in small dogs such as Beagles.

Sono-urethrography is a technique used to evaluate the integrity of the urethra utilizing fluid dilation of the urethral lumen. The purpose of this prospective, method comparison, pilot study was to investigate the feasibility of sono-urethrography in male dogs and to compare the quality of the images obtained using three different contrast solutions. The prostatic, membranous, and penile urethra was evaluated using saline, agitated saline, and ultrasound contrast agent (Sonovue) in 10 adult, male Beagles. Visibility of the urethral wall was better with sono-urethrography than with conventional ultrasonography, and the conspicuity of urethra could be assessed using all solutions. Hyperechoic lines created by agitated saline and Sonovue were more useful than anechoic saline in allowing identification of the urethra. Visibility scores for the internal margin of the urethral wall using sono-urethrography were significantly higher with saline and one-minute post agitated saline injection. However, the individual layers of the urethral wall could not be observed, regardless of the contrast solution used. Shadowing created by the pelvic bone deteriorated the window through which the urethra could be visualized, and this could not be overcome using sono-urethrography. The results of this study indicated that sono-urethrography is a feasible option for the visualization of the male urethra in dogs. The authors recommend sono-urethrography using saline or agitated saline infusion to evaluate the urethral wall and lumen. Sono-urethrography using ultrasound contrast agent can be applied to assess the integrity of the urethra by improving its conspicuity.

OBJECTIVE To investigate the effects of respiratory phase, body position, beam center location, and gastric distention on radiographic assessment of liver size in dogs. ANIMALS 12 Beagles. PROCEDURES Liver length and the ratio of liver length to T11 length were determined on lateral radiographic views obtained with various techniques. Images were acquired at maximal expiration or maximal inspiration, with dogs in right or left recumbency, with the beam centered on the caudal border of the scapula or the 13th rib, and after food was withheld or with gastric distention. Effects on organs adjacent to the liver were assessed with CT. Changes of the thoracic cavity during the respiratory cycle were investigated with fluoroscopy. RESULTS Liver length was significantly greater on radiographs obtained at maximal expiration than at maximal inspiration, but there was no increase in the ratio of liver length to T11 length. Body position, beam center location, and gastric distention did not significantly affect liver size. For CT, location of the spleen and stomach and location or size of the liver did not change markedly between right and left recumbency. Fluoroscopy revealed that thoracic width was less at maximal expiration than maximal inspiration. CONCLUSIONS AND CLINICAL RELEVANCE Liver length was greater at maximal expiration than at maximal inspiration because of a smaller thoracic width. Body position, beam center location, and gastric distention did not affect liver length. The ratio of liver length to T11 length was not significantly affected by any of the factors investigated.

Hormonal and vascular changes affecting the canine prostate after castration were investigated to identify the effects of hormones and perfusion on the development of benign prostatic hyperplasia (BPH). Concentrations of serum testosterone and estrogen and intraprostatic dihydrotestosterone (DHT) were compared between 5 normal dogs, 6 dogs with mild BPH, and 6 dogs with marked BPH. In addition, prostatic perfusion using contrast-enhanced ultrasonography (CEUS) and CT perfusion (CTP), as well as CT volumes of the prostates were compared. The changes in these values following castration were assessed in 6 dogs with marked BPH. CEUS revealed significantly slower prostatic arterial inflow and relatively faster venous outflow in BPH versus normal prostate. Permeability and blood volume were not significantly different between the groups via CTP. Intraprostatic DHT level was higher in BPH than in normal prostate and decreased significantly following castration, which was accompanied by a rapid decrease in prostatic volume. On CEUS, arterial inflow to the prostate significantly decreased following castration. Blood volume within the prostate decreased significantly by day 60 following castration. Permeability increased significantly during the early phase after castration; however, by day 60 post-castration, all perfusion parameters decreased significantly. Perfusion changes including venous parameters measured by CEUS and blood volume changes measured by CTP, however, did not support the backflow theory postulating that BPH is induced by vascular changes from congested testes. The major etiology for the development of BPH is attributed to be increased levels of DHT rather than vascular changes.

Computed tomography angiography is widely used for the assessment of various mesenteric vascular and bowel diseases in humans. However, there are only few studies that describe CT angiography application to mesenteric vessels in dogs. In this prospective, experimental, exploratory study, the mesenteric vasculature and enhancement pattern of the intestinal wall were evaluated on triple-phase CT angiography, and improvement of the visibility of vasculature was assessed on multiplanar reformation, maximum intensity projection, and volume rendering technique. After test bolus scanning at the level of the cranial mesenteric artery arising from the aorta, mesenteric CT angiography was performed in 10 healthy, male, Beagle dogs. Scan delay was set based on time-to-attenuation curves, drawn by placing the regions of interest over the aorta, intestinal wall, and cranial mesenteric vein. Visualization and enhancement of mesenteric arteries and veins were evaluated with multiplanar reformation, maximum intensity projection, and volume rendering techniques. The degree of intestinal wall enhancement was assessed on the transverse images in precontrast, arterial, intestinal, and venous phases. Pure arterial images were obtained in the arterial phase. Venous phase images allowed good portal vascular mapping. All CT angiography images were of high quality, allowing for excellent visualization of the anatomy of mesenteric vasculature including the small branches, particularly on maximum intensity projection and volume rendering technique. Distinct contrast enhancement of the intestinal wall was observed in both intestinal and venous phases. Findings indicated that this technique is feasible for the evaluation of mesenteric circulation in dogs.

This study was performed to evaluate the feasibility of ultrasound-guided computed tomography (CT) cholecystography and to establish an optimal protocol. In 8 healthy beagles, CT cholecystography was conducted using four contrast formulas; two dilution ratios (1:1 vs. 1:3) and two total volumes (8 mL vs. 16 mL) of 300 mgI/kg iohexol after ultrasound-guided percutaneous contrast injection into the gallbladder. CT images were obtained at 3, 10, and 30 min after injection and assessed qualitatively and quantitatively. For all contrast formulas, CT cholecystography showed the gallbladder and the intra- and extrahepatic bile ducts. The volume of the gallbladder and size of bile duct were significantly larger when using a volume of 16 mL iohexol than an 8 mL volume regardless of the dilution ratio. The distinction between the common bile duct and duodenum, the filling of the gallbladder, and the patency of bile duct were effectively assessed using a 16 mL volume of contrast agent with either dilution ratio. Beam-hardening artifacts deteriorated CT image quality for visualizing the biliary system when using the dilution ratio of 1:1. Patency of the bile tract could be easily evaluated using a curvilinear planar reconstruction. There was no significant difference in CT scan time among the different conditions. Minor leakage of contrast agent temporarily occurred after contrast injection in 30% of 32 sets of CT cholecystography. Ultrasound-guided percutaneous cholecystography can visualize both gallbladder and biliary tract with minimal artifacts using a contrast agent volume of 16 mL with a 1:3 dilution ratio.

OBJECTIVE To evaluate acute changes of the liver by use of shear wave elastography (SWE) and CT perfusion after radiofrequency ablation (RFA). ANIMALS 7 healthy Beagles. PROCEDURES RFA was performed on the liver (day 0). Stiffness of the ablation lesion, transitional zone, and normal parenchyma were evaluated by use of SWE, and blood flow, blood volume, and arterial liver perfusion of those regions were evaluated by use of CT perfusion on days 0 and 4. All RFA lesions were histologically examined on day 4. RESULTS Examination of the SWE color-coded map distinctly revealed stiffness of the liver tissue, which increased from the normal parenchyma to the transitional zone and then to the ablation zone. For CT perfusion, blood flow, blood volume, and arterial liver perfusion decreased from the transitional zone to the normal parenchyma and then to the ablation zone. Tissue stiffness and CT perfusion variables did not differ significantly between days 0 and 4. Histologic examination revealed central diffuse necrosis and peripheral hyperemia with infiltration of lymphoid cells and macrophages. CONCLUSIONS AND CLINICAL RELEVANCE Coagulation necrosis induced a loss of blood perfusion and caused tissue hardening (stiffness) in the ablation zone. Hyperemic and inflammatory changes of the transitional zone resulted in increased blood perfusion. Acute changes in stiffness and perfusion of liver tissue after RFA could be determined by use of SWE and CT perfusion. These results can be used to predict the clinical efficacy of RFA and to support further studies, including those involving hepatic neoplasia.