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.
OBJECTIVE To evaluate dynamic movement of the diaphragm of clinically normal dogs by use of fluoroscopy and to obtain quantitative data of diaphragmatic excursion during spontaneous breathing.
ANIMALS 8 healthy male Beagles with no history of respiratory tract disease.
PROCEDURES Fluoroscopy was performed during stabilized respiratory conditions. The beam center was located at the level of the diaphragm, and diaphragmatic motion was recorded during 3 respiratory cycles in dogs positioned in left lateral, right lateral, and dorsal recumbency. Extent of excursion of the diaphragmatic cupula and both crura, difference in excursion between the left and right crura, and ratios of the excursions of the diaphragmatic cupula and left and right crura to the length of the eighth thoracic vertebra were determined.
RESULTS Diaphragmatic crural excursion was symmetric for dogs in right lateral recumbency, and the crural excursion was approximately three-quarters of the vertebral length; however, crural excursion appeared to be asymmetric for dogs in left lateral recumbency. Mean ± SD difference in excursion between the right and left crura was 22.68 ± 8.68% for left lateral recumbency, 16.63 ± 9.22% for right lateral recumbency, and 18.11 ± 12.96% for dorsal recumbency.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that the fluoroscopic view of a dog positioned in right lateral recumbency may allow better evaluation of the symmetry of diaphragmatic excursion, compared with results for other recumbency positions. This study provided quantitative data on the excursion of diaphragmatic movement observed by use of fluoroscopy in clinically normal Beagles.
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.
20 healthy dogs and 20 dogs with tumors.
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.
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.
To evaluate the effect of slice thickness on CT perfusion analysis of the pancreas in healthy dogs.
12 healthy Beagles.
After precontrast CT scans, CT perfusion scans of the pancreatic body were performed every second for 30 seconds by sequential CT scanning after injection of contrast medium (iohexol; 300 mg of 1/kg) at a rate of 3 mL/s. Each dog underwent CT perfusion scans twice in a crossover-design study with 2 different slice thicknesses (2.4 and 4.8 mm). Computed tomographic pancreatic perfusion variables, including blood flow, blood volume determined with the maximum slope model, times to the start of enhancement and peak enhancement, permeability, and blood volume determined by Patlak plot analysis, were measured independently by 2 reviewers. The CT perfusion variables were compared between slice thicknesses. Interoperator reproducibility was determined by ICC calculation.
Interoperator reproducibility of CT perfusion variable measurements was excellent on 2.4-mm (mean ± SD ICC, 0.81 ± 0.17) and 4.8-mm (0.90 ± 0.07) slice thicknesses, except for time to peak pancreatic enhancement on 2.4-mm-thick slices, which had moderate reproducibility (intraclass correlation coefficient, 0.473). There was no significant difference in measurements of blood flow, blood volume by either method, times to the start and peak of pancreatic enhancement, or permeability between slice thicknesses.
CONCLUSIONS AND CLINICAL RELEVANCE
Results supported that a thin slice thickness of 2.4 mm can be used for assessment of pancreatic perfusion variables in healthy dogs.
To evaluate the sedative effect of a combination of butorphanol and midazolam on 2-D shear wave elastography (SWE) of the kidneys and pancreas in dogs.
8 clinically healthy dogs.
We conducted a 2-D SWE examination of the bilateral kidneys and the pancreas before and after IV of 0.2 mg/kg butorphanol and 0.1 mg/kg midazolam in each dog. We performed 2-D SWE on the left kidney via a subcostal approach with the dog in right lateral recumbency, on the right kidney via the intercostal approach with the dog in left lateral recumbency, and on the right lobe of the pancreas via the subcostal approach. Subsequently, the pancreas and kidney shear wave velocities (SWV) pre- and postsedation were compared.
On qualitative evaluation using color mapping, the pancreas and kidneys showed a homogeneous blue-to-green color in pre- and post-sedation 2-D SWE. There was no significant difference in SWV pre- and post-sedation in the pancreas and kidneys.
Intravenous administration of a combination of 0.2 mg/kg butorphanol and 0.1 mg/kg midazolam did not change the 2-D SWE of the pancreas and kidneys significantly. The combination of butorphanol and midazolam can be used in healthy dogs for 2-D SWE evaluation of the pancreas and kidneys, especially when the patient is uncooperative during the examination.
OBJECTIVE To determine the scan delay for use in performing cardiac CT angiography in dogs.
ANIMALS 4 clinically normal adult Beagles.
PROCEDURES In a crossover study, 12 formulations of iohexol solutions differing in iodine dose (300, 400, and 800 mg/kg) and concentration (undiluted and diluted 1:1, 1:2, and 1:3 with saline [0.9% NaCl] solution) were administered IV to each dog. Dynamic CT angiography was performed to evaluate enhancement characteristics of each formulation, with the region of interest set over the aorta. Time-attenuation curves (TACs) were obtained and analyzed.
RESULTS Peak arc–type TACs were obtained after administration of all undiluted formulations. Curve shape changed from peak arc type to plateau type as the total volume of the contrast solution (ie, dilution) increased. Prolonged peaks characteristic of plateau-type TACs suggested that a sufficient period of homogeneous attenuation could be achieved for CT scanning with administration of higher iohexol dilutions (1:2 or 1:3) containing higher iodine doses (400 or 800 mg/kg). In particular, attenuation values for plateau-type TACs remained between 200 and 300 Hounsfield units for > 16 seconds after the plateau endpoint was reached for 1:2 and 1:3 dilutions containing an iodine dose of 800 mg/kg. Scan delays of 13 to 17 seconds were computed for those 2 formulations.
CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that for clinically normal dogs, a scan delay of 13 to 17 seconds could be used to perform cardiac CT angiography with iohexol solutions containing an iodine dose of 800 mg/kg at dilutions of 1:2 or 1:3.
Objective—To determine the effect of region of interest (ROI) setting and slice thickness on trabecular bone mineral density (BMD) measured with quantitative CT in dogs.
Animals—14 healthy Beagles.
Procedures—CT of the lumbar vertebrae and a quantitative CT phantom was performed. The BMD of trabecular bone was measured from L1 to L7 in 2 ways in all dogs. First, sequential 9.6-mm-thick CT images were acquired and then CT images were reconstructed into transverse CT images with slice thicknesses of 2.4, 4.8, and 9.6 mm. The obtained images were analyzed by circular ROI and trace ROI methods. Second, lumbar vertebrae were scanned with the installed quantitative CT protocol with a slice thickness of 10 mm and then the CT images were analyzed by installed automatic BMD software.
Results—Interclass correlation coefficients of the automatic software (0.975 to 1.0) and the circular method (0.871 to 0.996) were high, compared with those of the trace method (0.582 to 0.996). The BMD measured with the automatic software was not significantly different from that measured with circular ROI and a slice thickness of 9.6 mm. The BMD measured by use of the circular method was not different according to slice thickness.
Conclusions and Clinical Relevance—Results obtained by use of automatic software were similar to those obtained by use of more manual methods. The CT images with thinner slice thickness (2.4 and 4.8 mm) could be used in dogs of toy and small breeds to measure lumbar vertebrae BMD to reduce the limitations of the standard 10-mm slice thickness.
OBJECTIVE To evaluate whether a low-dosage regimen of prednisolone induces bone loss and whether administration of alendronate sodium prevents glucocorticoid-induced osteopenia in dogs by measuring trabecular bone mineral density (BMD) with quantitative CT.
ANIMALS 8 healthy Beagles.
PROCEDURES In 4 dogs, prednisolone was administered PO at a dosage of 2 mg/kg once daily for 2 weeks, 1 mg/kg once daily for 4 weeks, and 0.5 mg/kg once daily for 3 weeks. In the other 4 dogs, alendronate sodium (2 mg/kg, PO, q 24 h) was whether administered for 9 weeks in addition to the same dosage of prednisolone used in the prednisolone-treated dogs. Before (day 0 [baseline]) and 21, 42, 63, and 150 days after the start of treatment, BMD of the lumbar vertebrae was measured by quantitative CT.
RESULTS BMD in the prednisolone treatment group decreased to 84.7% of the baseline value on day 42, increased to 87.9% on day 63, and recovered to 91.6% on day 150. In the prednisolone-alendronate treatment group, BMD decreased to 91% of the baseline value on day 21, increased to 93.8% on day 63, and then recovered to 96.7% on day 150. Bone mineral density in the prednisolone treatment group was generally lower, albeit not significantly, than that of the prednisolone-alendronate treatment group on each examination day.
CONCLUSIONS AND CLINICAL RELEVANCE BMD temporarily decreased after low-dosage prednisolone administration; however, it gradually improved during tapering of the prednisolone dosage. These results have suggested that a low dosage of prednisolone can be used with little concern for development of osteopenia in dogs.
To compare qualitative features and quantitative parameters of 2 contrast agents (sulfur hexafluoride microbubbles [SHM; SonoVue] and perfluoro-butane [PFB; Sonazoid]) for performance of contrast-enhanced ultrasonography (CEUS) of the pancreas in dogs.
8 healthy Beagles.
In a crossover study design, CEUS of the pancreas was performed twice in each dog, once with SHM and once with PFB, in random order with at least 3 days between examinations. The recorded cine images were qualitatively assessed for homogeneity of pancreatic enhancement and conspicuity of the pancreatic signal relative to the background. For the quantitative assessment, circular regions of interest were placed over the pancreatic body, and a time-intensity curve was obtained. For each region of interest, CEUS parameters including peak intensity (PI), time to peak pancreatic enhancement, area under the curve (AUC), and wash-in rate were obtained.
The homogeneity of the pancreatic parenchyma was not significantly different between contrast agents. The signal conspicuity relative to background noise was significantly higher with PFB than with SHM. Mean values of PI, wash-in rate, and AUC were significantly higher with PFB than with SHM. Time to peak enhancement was not significantly different between contrast agents.
CONCLUSIONS AND CLINICAL RELEVANCE
Pancreatic CEUS with SHM and PFB produced similar homogeneity scores, but only PFB provided excellent signal conspicuity. Perfluorobutane produced higher values of PI, wash-in rate, and AUC. Findings indicated that PFB can provide homogeneous and strong enhancement of the pancreas during CEUS in healthy dogs and that pancreatic CEUS parameter values differ with the contrast agent used.
To investigate the change in the lumbosacral angle (ΔLSA) and conus medullaris (CM) displacement in healthy dogs undergoing dynamic MRI with changes in the posture of their pelvic limbs from neutral posture to flexion or extension posture and to evaluate for potential correlation between ΔLSA and CM displacement.
9 healthy adult Beagles.
Dogs underwent dynamic MRI with their pelvic limbs positioned in neutral, flexion, and extension postures. From T2-weighted sagittal midline plane MRI images, 2 observers measured the lumbosacral angle and CM location in duplicate for each posture for each dog. Intra- and interobserver agreement was assessed, and the Spearman rank correlation coefficient (ρ) was used to assess for potential correlation between ΔLSA and CM displacement for changes in pelvic limb posture from neutral to flexion or extension.
Overall, the mean ΔLSA and CM displacement for changes in posture were 23° and 9.09 mm (caudal displacement) for the change from neutral to flexion posture, 8.4° and −2.5 mm (cranial displacement) for the change from neutral to extension posture, and 32.2° and 11.64 mm (caudal displacement) for the change from extension to flexion posture. The ΔLSA strongly correlated (ρ = 0.705; 95% CI, 0.434 to 0.859) with displacement of the CM.
CONCLUSIONS AND CLINICAL RELEVANCE
The use of dynamic MRI, compared with conventional MRI, will better help to characterize clinically normal and abnormal features of the lumbosacral region of the vertebral column and associated spinal cord during postural changes. Further, when limited translocation of the CM is evident on dynamic MRI, veterinarians should suspect underlying lumbosacral pathophysiologic processes or anatomic abnormalities.