TRUNCATION ARTIFACT IN MAGNETIC RESONANCE IMAGES OF THE CANINE SPINAL CORD.

The truncation artifact in magnetic resonance (MR) images is a line of abnormal signal intensity that occurs parallel to an interface between tissues of markedly different signal intensity. In order to demonstrate the truncation artifact in sagittal images of the canine spinal cord and the effect of changing spatial resolution, we conducted an experimental in vitro study. A section of fixed canine spinal cord was imaged using a 1.5T magnet. Spatial resolution was increased by increasing the acquisition matrix and reconstruction matrix, producing series of T2-weighted (T2w) images with the following pixel sizes: A, 1.6 (vertical) × 2.2 mm2 (horizontal); B, 1.2 × 1.7 mm2 ; C, 0.8 × 1.1 mm2 ; D, 0.4 × 0. 6 mm2 . Plots of mean pixel value across the cord showed variations in signal intensity compatible with truncation artifact, which appeared as a single, wide central hyperintense zone in low-resolution images and as multiple narrower zones in high spatial resolution images. Even in images obtained using the highest spatial resolution available for the MR system, the edge of the spinal cord was not accurately defined and the central canal was not visible. The experiment was repeated using an unfixed spinal cord specimen with focal compression applied to mimic a pathologic lesion. Slight hyperintensity was observed within the spinal cord at the site of compression although the cord was normal histologically. Results of this study suggest that caution should be applied when interpreting hyperintensity affecting the spinal cord in T2w sagittal images of clinical patients because of the possibility that the abnormal signal could represent a truncation artifact.

A description of a technique for ultrasound-guided lumbar plexus catheter in dogs: cadaveric study.

OBJECTIVE: To describe an ultrasound-guided approach for lumbar plexus catheter placement in dogs. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: Eleven thawed canine cadavers (13 ± 2 kg). MATERIAL AND METHODS: A technique to place a catheter in the psoas compartment at the level of the lumbar plexus under ultrasound guidance was described. Ultrasonographic landmarks for the placement of a lumbar plexus catheter were identified as the body of the sixth lumbar vertebrae, the psoas muscle and the femoral nerve. All catheters were placed by the principal investigator using epidural sets with an 18-G Tuohy needle. The procedure was carried out twice in each cadaver, with the aim of placing a catheter at the point of the left and right lumbar plexuses. A total volume of 0.4 mL kg(-1) of 1% methylene blue solution was injected into the psoas compartment after which the catheter was removed. After performing the injection in four cadavers, the technique was modified, altering the angle of needle placement and length of catheter insertion. Staining of the femoral and obturator nerves was assessed. Success was recorded if both nerves were stained over a length >1 cm. The spreading of the dye into the abdomen or to the nerve roots was also recorded. RESULTS: The success rate after the first four cadavers was four out of eight, and dye was found in the abdomen of two of the cadavers. When the modified technique was used in the subsequent seven cadavers, the success rate was 12 out of 14, and no dye was found in the abdomens. CONCLUSIONS AND CLINICAL RELEVANCE: This technique has shown a high percentage of success and low rate of complications. The only complication investigated in this study was the spread to the abdomen or epidural space. To establish safety, clinical studies will be needed.

Description and evaluation of four ultrasound-guided approaches to aid spinal canal puncture in dogs.

OBJECTIVE: To describe four ultrasound-guided approaches to the lumbar and thoracic spine to aid spinal canal puncture in the dog and to evaluate the feasibility of the technique. STUDY DESIGN: Prospective experimental study. ANIMAL POPULATION: Two canine cadavers. METHODS: In the first part of the study, the ultrasonographic appearance of the interlaminar space in the lumbosacral, lumbar and thoracic regions was described. In the second part of the study, four operators attempted a real-time, ultrasound-guided approach to the vertebral canal. Each operator performed the technique 20 times in total: five times at the lumbosacral junction, five in the thoracic region, five in the lumbar region with an in-plane approach, and five in the lumbar region with an out-of-plane approach. Computed tomography (CT) was used to confirm the position of the needle. The procedure was considered successful when the tip of the needle was observed within the vertebral canal. The success rate was calculated for each approach and operator. Fisher's exact test was used to compare differences between approaches and operators. RESULTS: In all cases, visualization of a ventral, parallel and straight hyperechoic line (floor of the vertebral canal) was considered a necessary prerequisite for successful positioning of the needle within the vertebral canal. A straight hyperechoic line (ligamentum flavum or dura mater) closer to the ultrasound probe was visualized in both the median lumbosacral approach and the transverse lumbar approach. The success rate overall was 81%; for the lumbosacral approach, 100%; for the thoracic approach, 80%; for the in-plane lumbar approach 95%; and for the out-of-plane lumbar approach, 45%. These differences were statistically significant (p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: The sonographic description of these approaches was considered adequate for performing spinal canal puncture. In-plane techniques achieved a higher success rate than out-of-plane ones. Further studies are needed to evaluate them in a clinical setting.

Comparison of computed tomographic and pathologic findings in 17 dogs with primary adrenal neoplasia.

The CT appearance of canine adrenal masses has been reported, but associations between imaging features and pathologic features of these lesions have not been investigated in detail. The purpose of this study was to test associations between different types of adrenal neoplasia and their CT and pathologic features. A retrospective cross-sectional study was performed and inclusion criteria were histologic diagnosis of primary adrenal neoplasia, contrast-enhanced CT examination of the abdomen and surgical resection of the mass or necropsy examination. For all included dogs, CT images and histopathologic specimens were reviewed independently by two veterinary radiologists and a veterinary pathologist, respectively. Seventeen dogs met inclusion criteria. Diagnoses were adenocarcinoma in nine (53%) dogs, pheochromocytoma in five (29%) dogs, and adenoma in three (18%) dogs. Pheochromocytoma was associated with CT signs of vascular invasion (likelihood ratio = 4.8, 95% CI = 1.3-18.3, P = 0.03) and macroscopic vascular invasion (likelihood ratio = 9.6, 95% CI = 1.4-65.9, P = 0.02). There was excellent agreement between signs of vascular invasion in CT images and vascular invasion at surgery or necropsy (kappa = 0.86, P = 0.001). A peripheral contrast-enhancing rim in delayed postcontrast CT images was associated with fibrous encapsulation of the tumor (kappa = 0.53, P = 0.05), and a heterogeneous pattern of contrast distribution in delayed postcontrast CT images was associated with adrenal hemorrhage or infarction on histological examination (kappa = 0.45, P = 0.05). Findings indicated that CT enabled assessment of adrenal neoplasia features that reflected their biological behavior and pathological findings, however overlapping characteristics between tumor types limited the potential for reliably distinguishing them based on CT alone.

Use of transsplenic injection of agitated saline and heparinized blood for the ultrasonographic diagnosis of macroscopic portosystemic shunts in dogs.

We describe the use of ultrasonography-guided percutaneous splenic injection of agitated saline and heparinized blood for the diagnosis of portosystemic shunts (PSS) in 34 dogs. Agitated saline mixed with 1 ml of heparinized autologous blood was injected into the spleen of 34 sedated dogs under sonographic guidance. The transducer was then sequentially repositioned to visualize the portal vein, the caudal vena cava, and the right atrium through different acoustic windows. It was possible to differentiate between intrahepatic and extrahepatic shunts depending on the entry point of the microbubbles into the caudal vena cava. Portoazygos shunts and portocaval shunts could be differentiated based on the presence of microbubbles in the caudal vena cava and/or the right atrium. In one dog, collateral circulation due to portal hypertension was identified. In dogs with a single extrahepatic shunt, the microbubbles helped identify the shunting vessel. The technique was also used postoperatively to assess the efficacy of shunt closure. All abnormal vessels were confirmed by exploratory laparotomy or with ultrasonographic identification of the shunting vessel. Ultrasound-guided transsplenic injection of agitated saline with heparinized blood should be considered as a valuable technique for the diagnosis of PSS; it is easy to perform, safe, and the results are easily reproducible.

Ultrasonographic appearance of the intravascular transit of agitated saline in normal dogs following ultrasound guided percutaneous splenic injection.

Portosystemic shunts (PSSs) allow portal blood to bypass the liver and enter the systemic circulation. Definitive diagnosis requires surgical identification, positive contrast portography, ultrasonography, or scintigraphy. This study was designed as a preliminary step to developing an alternative/adjuvant protocol to these imaging modalities. The main goals were to establish a technique for ultrasound-guided percutaneous trans-splenic injection of agitated saline, to evaluate the feasibility of performing the test to explore the postsplenic portal vasculature highlighted by the microbubbles, and to ascertain whether agitated saline microbubbles cross the sinusoidal barrier. Agitated saline was injected into the spleen of 20 healthy sedated dogs under sonographic guidance. The transducer was then repositioned to visualize the portal vein, the caudal vena cava, and the right atrium through different acoustic windows. Satisfactory results were achieved in all dogs. The microbubbles were visualized in all dogs as small intense echo signals within the portal vein at the level of the porta hepatis immediately after injection. In 18 out of 20 dogs, the echogenic signal of the microbubbles disappeared immediately once within the hepatic parenchyma, whereas in two dogs, the echoes from the microbubbles lasted for several seconds within the intrahepatic portal vasculature. The absence of microbubbles beyond the sinusoidal barrier in all of the healthy dogs included in this study makes trans-splenic injection of agitated saline a candidate as an adjuvant technique for the diagnosis of PSS, being easy to perform and repeat, as well as safe and technically feasible.

Pathologic correlation of resistive and pulsatility indices in canine abdominal lymph nodes.

We assessed the ability of the resistive index (RI) and pulsatility index (PI) to allow differentiation between normal, reactive, and neoplastic lymph nodes. Forty-seven medial iliac and 54 mesenteric lymph nodes from 83 dogs were evaluated sonographically. A cytologic sample was obtained in each dog that allowed categorization into one of the categories defined above. We found a significant difference in the RI and PI in nonneoplastic vs. neoplastic medial iliac and mesenteric lymph nodes. Values higher than 0.67 for the RI and 1.02 for the PI in medial iliac lymph nodes and higher than 0.76 for the RI and 1.23 for the PI in mesenteric lymph nodes had a high sensitivity and specificity for differentiating benign from neoplastic lymph nodes.