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- Author or Editor: George Voorhout x
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Objective—To assess intra- and interobserver repeatability of ocular biometric measurements obtained by means of high-resolution B-mode ultrasonography in dogs.
Animals—6 Beagles without ocular abnormalities.
Procedures—B-mode ultrasonography was performed bilaterally with a 10.5-MHz broadband compact linear array transducer. All measurements were made on 2 different occasions by 2 observers. The Bland-Altman method was used to assess agreement between measurements obtained by the 2 observers and between the 2 sets of measurements obtained by each observer.
Results—Intra- and interobserver repeatability was highest for larger measurements, such as depth of the eye and depth of the anterior chamber. When repeatability was examined, bias was significantly different from 0 for only a few measurements, but the percentage difference between observations was as high as 180% for some measurements.
Conclusions and Clinical Relevance—Results suggest that most measurements of intraocular distances and structures obtained by means of high-resolution B-mode ultrasonography have acceptable intra- and interobserver repeatability. However, the percentage difference between observations can be high for smaller measurements.
Objective—To determine the reproducibility and accuracy of computed tomographic (CT) measurements of pituitary gland dimensions in healthy dogs.
Animals—35 healthy sexually intact adult dogs.
Procedures—2 observers independently viewed CT images of the skull in 35 dogs twice. Pituitary gland height, width, length, and volume and pituitary gland height–to–brain area ratio (P:B ratio) were measured or calculated. Intraobserver and interobserver agreement indexes (AIs) were calculated for pituitary gland dimensions. Computed tomography was performed also on 5 phantoms, and both observers measured phantom dimensions twice. True-value AIs were calculated for the phantom study.
Results—The mean ± SD interobserver AI between observer 1 and 2 for pituitary gland height and the P:B ratio was 0.90 ± 0.07. The intraobserver AI for pituitary gland height and the P:B ratio was 0.97 ± 0.04 for observer 1 and 0.94 ± 0.04 for observer 2. The intraand interobserver AIs for the other dimensions were lower than those for pituitary gland height and the P:B ratio. All phantom dimensions on CT images were underestimated significantly, compared with their true values.
Conclusions and Clinical Relevance—The intra- and interobserver AIs for pituitary gland dimension measurements on CT images were high. However, the same observer preferably should perform serial measurements. Window settings influence pituitary gland dimension measurements, and predetermined window settings are recommended to make comparisons among dogs. Pituitary gland dimension measurements made from CT images in our study underestimated the true values.
Objective—To evaluate thin-slice 3-dimensional gradient-echo (GE) magnetic resonance imaging (MRI) of the pituitary gland in healthy dogs.
Animals—11 healthy dogs.
Procedures—By use of a 0.2-Tesla open magnet, MRI of the skull was performed with T1-weighted GE sequences and various protocols with variations in imaging plane, slice thickness, and flip angle before and after administration of contrast medium; multiplanar reconstructions were made. The pituitary region was subjectively assessed, and its dimensions were measured. Image quality was determined by calculation of contrast-to-noise and signal-to-noise ratios.
Results—Best-detailed images were obtained with a T1-weighted GE sequence with 1-mm slice thickness and 30° flip angle before and after administration of contrast medium. Images with flip angles > 50° were of poor quality. Quality of multiplanar reconstruction images with 1-mm slices was better than with 2-mm slices. The bright signal was best seen without contrast medium. With contrast medium, the dorsal border of the pituitary gland was clearly delineated, but lateral borders were more difficult to discern.
Conclusions and Clinical Relevance—MRI of the canine pituitary gland with a 0.2-Tesla open magnet should include a T1-weighted GE sequence with 1-mm slice thickness and flip angle of 30° before and after administration of contrast medium. The neurohypophysis was best visualized without contrast medium. The MRI examination permitted differentiation between the pituitary gland and surrounding structures.
Objective—To determine the contrast enhancement pattern of the pituitary gland in healthy dogs via dynamic computed tomography (CT).
Procedure—With each dog in sternal recumbency, transverse CT scans were made perpendicular to the skull base from the rostral clinoid processes to the dorsum sellae. At the position of the image that contained the largest cross section of the pituitary gland, a series of 9 to 11 scans was made during and after IV injection of contrast medium (dynamic CT scans). The contrast enhancement pattern of the pituitary gland and surrounding arteries was assessed visually and by use of time-density curves.
Results—After strong enhancement of the maxillary arteries, the intracavernous parts of the internal carotid arteries, and the communicating arteries of the arterial cerebral circle, there was a strong enhancement of the central part of the pituitary gland followed by enhancement of its peripheral part. On the last images of the dynamic series of the pituitary gland, the central part was hypodense, compared with the peripheral part. Time-density curves confirmed an early, strong enhancement of the central part and a delayed, less strong enhancement of the peripheral part of the gland.
Conclusions and Clinical Relevance—The difference in enhancement between the central and peripheral parts of the pituitary gland was attributable to a difference in vascularization of the neurohypophysis and adenohypophysis, respectively. Distortion or disappearance of the strong central enhancement (pituitary flush) may be used for the detection and localization of pituitary abnormalities in the adenohypophysis. (Am J Vet Res 2004;65:1518–1524)
Objective—To determine portal hemodynamic changes associated with surgical shunt ligation and establish ultrasonographic criteria for determining the optimal degree of shunt narrowing and predicting outcome.
Animals—17 dogs, each with a single congenital extrahepatic portosystemic shunt.
Procedure—Pre- and postligation flow velocities and flow directions were determined by Doppler ultrasonography intraoperatively in the shunt and in the portal vein cranial and caudal to the shunt origin. Outcome was evaluated 1 month after surgery by measuring blood ammonia concentration and performing abdominal ultrasonography.
Results—Hepatofugal flow was detected in 9 of 17 dogs before shunt attenuation in the portal segment that was between the shunt origin and the entering point of the gastroduodenal vein. If hepatofugal flow became hepatopetal after shunt ligation, hyperammonemia resolved. Hepatofugal portal flow was caused by blood that flowed from the gastroduodenal vein toward the shunt. Shunt attenuation converted hepatofugal flow to hepatopetal in the shunt in 12 of 17 dogs. Chronic portal hypertension developed or perioperative death occurred when the portal congestion index caudal to the shunt origin increased by > 3.6 times.
Conclusions and Clinical Relevance—After hepatopetal flow in the cranial portal vein and the shunt is established, further shunt narrowing is contraindicated. Increase of the portal congestion index caudal to the shunt > 3.5 times should be avoided. Poor outcome because of severe hypoplasia of the portal branches can be expected if the flow direction remains hepatofugal after shunt occlusion cranial to the shunt origin. ( J Am Vet Med Assoc 2004;224:395–402)
Objective—To assess the extent of agreement between computed tomography (CT), magnetic resonance imaging (MRI), and surgical findings in dogs with degenerative lumbosacral stenosis.
Animals—35 dogs with degenerative lumbosacral stenosis.
Procedures—Results of preoperative CT and MRI were compared with surgical findings with respect to degree and location of disk protrusion, position of the dural sac, amount of epidural fat, and swelling of spinal nerve roots.
Results—A lumbosacral step was seen on radiographic images from 22 of 32 (69%) dogs, on CT images from 23 of 35 (66%) dogs, and on MR images from 21 of 35 (60%) dogs. Most dogs had slight or moderate disk protrusion that was centrally located. There was substantial or near perfect agreement between CT and MRI findings in regard to degree of disk protrusion (kappa, 0.88), location of disk protrusion (0.63), position of the dural sac (0.89), amount of epidural fat (0.72), and swelling of spinal nerve roots (0.60). The degree of agreement between CT and surgical findings and between MRI and surgical findings was moderate in regard to degree and location of disk protrusion (kappa, 0.44 to 0.56) and swelling of spinal nerve roots (0.40 and 0.50).
Conclusions and Clinical Relevance—Results indicate that there is a high degree of agreement between CT and MRI findings in dogs with degenerative lumbosacral stenosis but that the degree of agreement between diagnostic imaging findings and surgical findings is lower.
Objective—To quantitatively assess distractioninduced bone formation in a crural lengthening model in dogs by use of delayed-image bone scintigraphy.
Animals—12 mature Labrador Retrievers.
Procedure—Dogs were randomly allocated to 1 of 3 groups. A circular external skeletal fixation system was mounted on the right crus of each dog. Osteotomy of the distal portion of the tibia and fibula was performed in groups 1 and 2 and was followed by a lengthening procedure of 10 mm in the first group only. The third group served as sham-operated controls. Delayed-image bone scintigraphy with technetium-99m hydroxy methylene diphosphonate was performed 2, 4, and 6 weeks after surgery. Delayedimage–to–region-of-interest, delayed-image–to–crural, and delayed-image–to–femoral scintigraphic activity ratios were calculated. New bone formation was quantified by use of densitometric image analysis, and values for the scintigraphic ratios were compared.
Results—In the distraction and osteotomy groups, delayed-image–to–region-of-interest and delayedimage-to-crural ratios increased significantly. Although densitometric image analysis revealed increased bone formation after distraction, the region-of-interest ratios and crural ratios were similar in both groups. All dogs had increased delayedimage–to–femoral ratios.
Conclusions and Clinical Relevance—Delayed-image bone scintigraphy ratios were not effective at differentiating between the amounts of distraction-induced bone and osteotomy-induced bone. Metabolic bone activity in the adjacent femur was increased as a consequence of circular external skeletal fixator placement. Delayed-image bone scintigraphy was not adequately sensitive to quantitatively monitor bone formation but may be useful as an early predictor of bone healing.
Objective—To compare the results of computed tomography (CT) and magnetic resonance imaging (MRI) of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism (PDH) caused by histologically confirmed pituitary adenoma.
Design—Retrospective case series.
Animals—11 dogs with PDH that underwent transsphenoidal hypophysectomy.
Procedures—Medical records of dogs examined between January 2001 and March 2003 were reviewed. Dogs were included in this study if they had clinical signs of hypercortisolism at the time of admission (for which PDH was diagnosed) and underwent transsphenoidal hypophysectomy. Pre- and postcontrast CT and low-field MRI (0.2-Tesla magnet) were performed on the same day as surgery for each dog.
Results—An abnormal pituitary gland was found in 7 dogs by use of MRI and in the same 7 dogs by use of CT. Significant differences were found between postcontrast CT and MR images for height, width, and length of the pituitary gland; brain area; and thickness of the sphenoid bone. However, the pituitary gland height-to-brain area ratio determined from postcontrast CT and MR images was not significantly different. The signal-to-noise ratio and contrast-to-noise ratio of pre- and postcontrast MR images were significantly higher than those of the CT images.
Conclusions and Clinical Relevance—Low-field MRI and dynamic CT imaging of the pituitary gland provided comparable information on the presence of pituitary adenomas in dogs with PDH.