COMPUTED TOMOGRAPHIC DETERMINATION OF TIBIAL TORSION IN THE DOG

The goal of this study was to develop a method for computed tomographic (CT) measurement of tibial torsion, and to compare this technique with direct anatomic measurement of tibial torsion in cadaveric canine tibiae. Paired hind limbs of 10 cadaveric dogs were mounted on a custom-designed limb holding apparatus. One-millimeter thick, contiguous, transverse CT slices were obtained from the distal femur to the proximal tibia and 2 mm CT slices were obtained from the distal tibia to the proximal tarsus. The tibiae were freed of soft tissues and digital photographic images of the proximal and distal articular surfaces were obtained with the camera lens aligned perpendicular to the long axis of the tibia. Multiple proximal and distal tibial axes were identified on the images; two proximal and two distal axes were found to be repeatable in all specimens in both the direct and CT methods. The torsion angle was calculated by determining the difference between the axis angles for each pair of proximal and distal axes. There was no significant difference in torsion angle identified between the direct photographic and CT method for any pair of proximal and distal axes. CT determination of tibial torsion is a rapid and accurate method, and warrants investigation in clinical patients.     

Comparison of radiographic and anatomic femoral varus angle measurements in normal dogs

Objective— To determine if the clinically practiced method of radiographic femoral varus angle (R-FVA) measurement is repeatable, reproducible, and accurate.
Study Design— Radiographic and anatomic study.
Animals/Sample Population— Normal Walker hound cadavers (n=5) and femora (n=10).
Methods— Cadavers were held in dorsally-recumbent and torso-elevated positions as 3 craniocaudal radiographs were made of each femur, by each of 2 different technicians. Femora were then harvested for direct measurement of anatomic femoral varus angle (A-FVA). R-FVA was measured on each radiograph by each of 3 examiners on 3 separate occasions. Intra-observer (repeatability) and inter-observer (reproducibility) variance in R-FVA measurement and the strength of relationship between R-FVA and A-FVA (accuracy) were determined.
Results— Mean (±SD) A-FVA was 5.2±2.1° (range, 2.4–8.2°). Mean (±SD) R-FVA was 5.8±1.0° (range, 2.7–9.6°). Intra-observer variance (range: 11–16%) and inter-observer variance (16%) were acceptable. The strength of relationship between measured R-FVA and A-FVA (maximum adjusted R²<0) was unacceptably low regardless of observer, patient position, or radiographic technician.
Conclusion— R-FVA measurement was repeatable and reproducible, but not statistically accurate in predicting A-FVA in these 5 normal Walker hounds. The detected inaccuracy may be real or the result of a selection bias for normal dogs obscuring the true relationship.
Clinical Relevance— R-FVA may not be an accurate method of femoral varus measurement in dogs with A-FVA<10°. Using Slocum's criteria for distal femoral osteotomy (R-FVA>10°), the procedure would not have been erroneously performed in any of the normal dogs of this study.     

VALIDATION OF A NOVEL TECHNIQUE FOR CREATING SIMULATED RADIOGRAPHS USING COMPUTED TOMOGRAPHY DATASETS

Understanding radiographic anatomy and the effects of varying patient and radiographic tube positioning on image quality can be a challenge for students. The purposes of this study were to develop and validate a novel technique for creating simulated radiographs using computed tomography (CT) datasets. A DICOM viewer (ORS Visual) plug‐in was developed with the ability to move and deform cuboidal volumetric CT datasets, and to produce images simulating the effects of tube‐patient‐detector distance and angulation. Computed tomographic datasets were acquired from two dogs, one cat, and one horse. Simulated radiographs of different body parts (n = 9) were produced using different angles to mimic conventional projections, before actual digital radiographs were obtained using the same projections. These studies (n = 18) were then submitted to 10 board‐certified radiologists who were asked to score visualization of anatomical landmarks, depiction of patient positioning, realism of distortion/magnification, and image quality. No significant differences between simulated and actual radiographs were found for anatomic structure visualization and patient positioning in the majority of body parts. For the assessment of radiographic realism, no significant differences were found between simulated and digital radiographs for canine pelvis, equine tarsus, and feline abdomen body parts. Overall, image quality and contrast resolution of simulated radiographs were considered satisfactory. Findings from the current study indicated that radiographs simulated using this new technique are comparable to actual digital radiographs. Further studies are needed to apply this technique in developing interactive tools for teaching radiographic anatomy and the effects of varying patient and tube positioning.     

Comparison of radiography and CT to identify changes in the skulls of four rabbits with dental disease

Four domestic pet rabbits with dental pathology were presented at a university clinic. In addition to conducting physical examinations of the rabbits, radiographic and computed tomographic (CT) images of the rabbits' heads were obtained. Three rabbits were euthanized at the owners' request, and anatomic sections of the skulls were made. The observations of the anatomic sections, radiographs, and CT images are described. The abnormalities found on the radiographs and CT images were very similar to the findings on the anatomic sections. Compared to radiography, the CT images provided more details about the extent of the dental pathology, which is likely to be important for establishing a more precise prognosis and a more informed decision making process.     

COMPARISON OF RADIOGRAPHY, MYELOGRAPHY AND COMPUTED TOMOGRAPHY FOR THE EVALUATION OF CANINE VERTEBRAL AND SPINAL CORD TUMORS IN SIXTEEN DOGS

Radiographic, myelographic and computed tomographic (CT) studies from sixteen dogs with histologically diagnosed vertebral or spinal cord neoplasia (seventeen lesions) were retrospectively evaluated. Radiographs were compared with CT images to evaluate vertebral bony changes (bone production, lysis or both). Myelographic and CT images were evaluated to separate lesions into one of three categories, extradural, intradural/extramedullary, or intramedullary. These findings were compared to histologic tumor type from surgical or necropsy samples. Histologically, seven lesions were vertebral tumors and were classified as extradural lesions; ten lesions were spinal cord tumors of which eight were classified as intradural/extramedullary and two as intramedullary. Using CT, the amount of bony change associated with extradural lesions was greater than or equal to the amount of bony change visualized using radiographs. Myelography more correctly differentiated between intradural/ extramedullary and intramedullary lesions than did CT, although three open diagnoses detracted from the CT results. This study suggests that when evaluating extradural lesions, the amount of bony change was better visualized using CT than survey radiographs. Myelography was better when compared to CT for classifying spinal cord lesions, however, standardization of the CT imaging protocol may help determine the specific clinical indications for using CT in dogs with suspected vertebral or spinal cord tumors.     

COMPUTED TOMOGRAPHIC AND RADIOGRAPHIC CHARACTERISTICS OF AORTIC LESIONS IN 42 DOGS WITH SPIROCERCOSIS

Spirocerca lupi is a common cause of vomiting, regurgitation, and sudden death in dogs that live in tropical or subtropical regions. Sudden death due to aortic rupture may occur with no preceding clinical signs. The purpose of this prospective study was to compare radiographic and computed tomographic (CT) characteristics of aortic lesions in a cohort of 42 dogs with endoscopically confirmed spirocercosis. Dorsoventral and right lateral recumbent thoracic radiographic findings were compared with pre‐ and postcontrast thoracic CT findings. Aortic mineralization was detected using CT in 18/42 dogs (43%). Three dogs had faint diffuse aortic wall mineralization. Using CT as the reference standard, radiographs had a sensitivity and specificity of 6% and 96%, respectively, for detecting aortic mineralization. A total of 20 aortic aneurysms were detected using CT in 15/42 dogs (36%). Using CT as the reference standard, radiographs had a sensitivity and specificity of 86% and 56%, respectively, for detecting aortic aneurysms. Respiratory motion, aortic displacement by esophageal masses and Spirocerca nodules adjacent to the aorta mimicked aneurysm formation on radiographs. Aortic thrombi were seen in two dogs in postcontrast CT images. Findings from this study indicated that aortic mineralization and aneurysm formation are common in dogs with spirocercosis. Findings also supported the use of pre‐ and postcontrast CT as effective methods for detecting and characterizing these lesions.     

Comparison of computed tomographic and standard radiographic determination of tibial torsion in the dog

OBJECTIVE: To compare the effect of internal tibial rotation on the computed tomographic (CT) and standard radiographic assessment of tibial torsion (TT) in dogs. STUDY DESIGN: In vitro study. SAMPLE POPULATION: Cadaveric canine hind limbs (6 pairs). METHODS: The cranial cruciate ligament was transected, and caudo-cranial radiographic and transverse CT images were obtained with the femur and tibiae in a neutral position, and after 15 degrees internal tibial rotation. Radiographic TT was determined by measuring the distance (d) between the calcaneus and the sulcus of the talus. CT determination of TT was performed using the proximal transcondylar and the distal cranial tibial axes. The distance (d) in the 2 groups and the difference in the CT determination of TT between groups were compared with a hypothetical mean value of 0 mm and 0 degrees, respectively. RESULTS: The mean distance (d) for the neutral radiographic group was not significantly different from 0 (P=.473); however, for the 15 degree group it was significantly different (P<.0001). The difference in the CT determination of TT did not differ from 0 (P=.317). CONCLUSION: The standard radiographic technique does not discriminate between internal TT and internal rotation of the tibia. Thus, dogs with normal tibial conformation can be depicted by radiography as torsed, whereas dogs with TT may be misinterpreted as normal because of arbitrary positioning. CLINICAL RELEVANCE: Lateral displacement of the medial border of the calcaneus on a caudo-cranial radiograph should not be used as the sole arbiter of TT before surgical correction.     

COMPUTED TOMOGRAPHY AND POSITIVE CONTRAST COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE CANINE SHOULDER: NORMAL ANATOMY AND EFFECTS OF LIMB POSITION ON VISIBILITY OF SOFT TISSUE STRUCTURES

Soft tissue injuries of the shoulder are an important cause of forelimb lameness in dogs. The objectives of this canine cadaver study were to describe normal anatomy of shoulder soft tissue structures using computed tomography (CT) and computed tomographic arthrography (CTA) and to determine the effects of positioning on visualization of shoulder soft tissue structures. Thirteen forelimbs were removed from eight canine cadavers. Two forelimbs were used for contrast dose optimization. For the remaining 11 forelimbs, shoulder CT and CTA were performed using three defined joint angles (140°, 90°, and 70°). For three forelimbs, CT and CTA images were compared with frozen anatomic sections to describe normal anatomy. Ten forelimbs were used for analysis of positioning effects. Soft tissue structures evaluated were the joint capsule, cartilage, ligaments, tendons, and muscles. A visual assessment score was assigned to each structure using a consensus of two observers. The range and mode of scores were calculated and compared for each modality and limb position. The shoulder joint capsule and medial and lateral glenohumeral ligaments were completely visible with CTA. All tendons and muscles were visualized in all the examinations except for the teres minor muscle tendon and the coracobrachialis muscle, which were not visible on all scans. Positioning the limb in an extended position significantly improved visualization of most soft tissue shoulder structures. Shoulder cartilage was best seen with CTA and with neutral or flexed positioning of the shoulder. Findings indicated that both CT and CTA are feasible imaging techniques for visualization of soft tissue structures of the canine shoulder.     

ANATOMIC REFERENCE FOR COMPUTED TOMOGRAPHY OF THE HEAD OF THE FOAL

The purpose of this study was to produce an anatomic reference for computed tomography (CT) of the head of the foal for use by radiologists, clinicians, and veterinary students. The head from each of 2 foals, euthanized for reasons unrelated to head pathology, was removed and prepared for CT scanning. Using a third-generation CT scanner, 5-mm contiguous transverse images were acquired. The heads were then frozen and sectioned using a band saw, with the cuts matched as closely as possible to the CT slices. The anatomic sections were photographed and radiographed. The radiographs and anatomic photographs were digitized and matched with the corresponding CT image. Each CT image was compared with its corresponding radiographic and anatomic section to assist in the accurate identification of specific structures. Clinically relevant structures were identified and labeled in corresponding images (CT, anatomic slice, and radiograph of slice). Only structures identified in the CT image were labeled in 1 of the other 2 images. Sagittal (reference) images of the horse's head were reconstructed from the transverse CT scans, and were used to indicate the level from which each of the transverse images was obtained. Corresponding labeled images were then formatted together with a legend for identification of specific anatomic structures.     

The relationship between the size of caudolateral curvilinear osteophyte of the canine femoral neck and the radiographic view

Caudolateral curvilinear osteophyte (CCO), an osteophyte at the site of joint capsule attachment on the caudal aspect of the femoral neck, has been advocated as a radiographic criterion for coxofemoral subluxation. The correlation between the presence of CCO on radiographs (radiographic-CCO), the size of the CCO (CCO index) on three-dimensional computed tomographic (CT) images, and hip evaluation using transverse CT images was assessed in 22 Border Collies. CCOs were detected on the radiographs and CT images of 32% and 100% femurs, respectively. The CCO index correlated significantly with radiographic-CCO, but a large CCO index did not necessarily imply that the CCO was visible on radiographs. Hence, radiographic-CCO findings should be used cautiously in hip evaluation of Border Collies.     

The diagnostic yield of conventional radiographs and computed tomography in dogs and cats with maxillofacial trauma

Objective— To compare the diagnostic yield of conventional radiographs and computed tomography (CT) images of the skulls of dogs and cats with maxillofacial trauma (MFT).
Study Design— Prospective study.
Animals— Dogs (n=9) and 15 cats with MFT.
Methods— CT-scans and skull radiographs (4 standard projections) for each animal were evaluated using a semi-quantitative scoring system for the ability to identify 26 predefined, clinically relevant anatomic features (Part 1), and 27 predetermined potential traumatic injuries (Part 2). For Part 1, mean scores for each anatomic feature were recorded for every view and imaging modality. For Part 2, studies were evaluated for the frequency of cases where each predetermined traumatic injury was identified.
Results— Part 1: On radiographs it was easy to identify 17 of 26 anatomic features whereas 6 features were very difficult or impossible to identify on any view. All structures were considered easy or very easy to identify on CT. Scores for CT were lower than radiographs for evaluating dental occlusion and the integrity of the mandibular body. Part 2: CT scans demonstrated 1.6 times more maxillofacial injuries for dogs and 2.0 times more for cats than conventional radiographs. The average number of MFT injuries per animal by radiographs and CT-scan was 4.8 and 7.6 in dogs, and 3.8 and 7.7 in cats, respectively.
Conclusion— CT is superior to conventional skull radiography for identification of anatomic structures and traumatic injuries in dogs and cats. Skull radiography is useful for visualizing the mandibular body and dental occlusion.
Clinical Relevance— CT allows for accurate assessment, diagnosis and treatment planning of MFT in dogs and cats.     

Computed Tomography Atlas of the Normal Cranial Canine Abdominal Vasculature Enhanced by Dual‐phase Angiography

This study was performed to provide a detailed atlas of the normal arterial and venous canine vasculature in the cranial abdomen by dual‐phase computed tomographic angiography. Five adult beagles were positioned in dorsal recumbency on a multislice helical CT scanner. An unenhanced survey CT scan from the diaphragm to the pelvic inlet was performed. Bolus‐tracking software was used for the dual‐phase angiogram, and contrast medium was administered in a cephalic vein. The arterial phase was scanned from the mid‐abdomen to the cranial aspect of the diaphragm; the portal phase was scanned a few seconds after the arterial phase in the opposite direction. The DICOM studies from all dogs were analysed. Representative images were selected and anatomic structures labelled. Maximum intensity projections and three‐dimensional images were generated using software techniques. A detailed atlas of the venous and arterial vasculature of the cranial canine abdomen was created with the help of bolus‐tracking dual‐phase computed tomographic angiography (CTA). Practitioners can use this anatomic atlas with its detailed venous and arterial phase CT angiograms of the canine cranial abdomen to compare normal versus abnormal vascular anatomy.     

ACCURACY OF MAGNETIC RESONANCE IMAGING FOR ESTIMATING INTRAMEDULLARY OSTEOSARCOMA EXTENT IN PRE-OPERATIVE PLANNING OF CANINE LIMB-SALVAGE PROCEDURES

The objective of this work was to compare the accuracy of radiographs and magnetic resonance imaging (MRI) for estimating appendicular osteosarcoma margins. The accuracy of computed tomography (CT) and bone scintigraphy was also assessed when these studies were available. Eight dogs with appendicular osteosarcoma underwent radiographic and MRI of affected limbs. In addition, bone scintigraphy was performed in six dogs and CT examination was performed in five dogs. Two observers jointly measured tumor length on all imaging studies. Correlative gross and histologic evaluation of all affected limbs was performed to determine tumor extent as measured from the nearest articular surface. Results from imaging studies were compared to gross and microscopic morphometry findings to determine the accuracy of each modality for determining tumor boundaries. MRI images were accurate with a mean overestimation of actual tumor length of 3 +/- 13%. T1-weighted non-contrast images were superior in identifying intramedullary tumor margins in most instances whereas contrast-enhanced images provided supplemental information in two dogs. Lateromedial and craniocaudal radiographs overestimated tumor length by 17 +/- 28% and 4 +/- 26%, respectively. Scintigraphy and CT overestimated tumor margins by 14 +/- 28% and 27 +/- 36%, respectively. MRI appears to be an accurate diagnostic imaging modality in determining intramedullary osteosarcoma boundaries. MRI should be considered as part of a pre-operative assessment of appendicular osteosarcoma, particularly when a limb-sparing procedure is contemplated.     

Comparison of thoracic radiographs and single breath-hold helical CT for detection of pulmonary nodules in dogs with metastatic neoplasia

Imaging studies in people indicate that x-ray computed tomography (CT) is a more sensitive technique than thoracic radiography for the detection of pulmonary metastasic neoplasia. Systematic studies comparing CT and thoracic radiographic techniques in veterinary patients have not been performed. The present retrospective study was designed to directly compare the efficacy of these 2 techniques in detecting pulmonary nodules in dogs. Eighteen dogs with histologically confirmed pulmonary metastatic neoplasia had contemporaneous thoracic radiographs and pulmonary CT scans compared. Quantitative analyses included estimation of pulmonary nodule size, number, and lobar distribution on thoracic radiographs and CT images. Only 9% of CT-detected pulmonary nodules were identified on thoracic radiographs (P < .003). The lower size threshold was approximately 1 mm to detect pulmonary nodules on CT images and 7-9 mm to reliably detect nodules on radiographs (P < .0001). Additionally, pulmonary nodules were detected in a significantly greater number of lung lobes using CT as compared with thoracic radiographs (P < .0001). These data indicate that CT is significantly more sensitive than thoracic radiography for detecting soft-tissue nodules in dogs. As such, thoracic CT should be considered in any patient with neoplasia that has potential for pulmonary metastasis to more reliably stage the disease, particularly when accurate characterization of the extent and distribution of pulmonary metastatic disease affects therapeutic planning.     

Computed tomographic features of the normal canine thyroid gland.

The computed tomographic (CT) features of the normal thyroid gland were compiled from images acquired in 25 client-owned dogs without thyroid gland disease. The mean pre- and postcontrast attenuation values were 107.5 and 169.0 Hounsfield Units, respectively. After injection of intravenous contrast medium (600 mg iodine/kg), the apparent thyroid gland volume (both lobes combined) increased from a mean value of 1148.0 nm3 to a mean value of 1188.9 mm3. All thyroid lobes were homogeneous on pre- and postcontrast images. In a craniocaudal direction, the gland spanned a region from the 1st to the 8th tracheal ring and the right lobe was often more cranial than the left. On transverse images the lobe shape was ovoid in 72%, and its location was dorsolateral to the trachea in 90% of dogs. Parathyroid glands could not be identified and an isthmus connecting both thyroid lobes was only seen in one dog. Considering the excellent visibility of the normal canine thyroid gland, CT can be beneficial in the differentiation of thyroidal versus nonthyroidal neck masses. CT also yields potential in the staging of thyroid carcinomas.     

Relationships among measurements obtained by use of computed tomography and radiography and scores of cartilage microdamage in hip joints with moderate to severe joint laxity of adult dogs

OBJECTIVE: To evaluate correlations among measurements on radiographic and computed tomography (CT) images with articular cartilage microdamage in lax hip joints of dogs. ANIMALS: 12 adult mixed-breed hounds. PROCEDURES: Pelvic CT and radiography were performed. Hip joints were harvested following euthanasia. Orthopedic Foundation for Animals (OFA) and PennHIP radiograph reports were obtained. Norberg angle (NA) and radiographic percentage femoral head coverage (RPC) were determined. Center-edge angle (CEA), horizontal toit externe angle (HTEA), ventral acetabular sector angle (VASA), dorsal acetabular sector angle (DASA), horizontal acetabular sector angle (HASA), acetabular index (AI), and CT percentage femoral head coverage (CPC) were measured on 2-dimensional CT images. Femoral head-acetabular shelf percentage was measured on sagittal 3-dimensional CT (SCT) and transverse 3-dimensional CT (TCT) images. Light microscopy was used to score joint cartilage. Relationships of OFA confirmation and PennHIP osteoarthritis scores with radiography, CT, and cartilage variables and relationships of cartilage scores with radiography and CT measurements were evaluated with Spearman rank correlations. Pearson correlation was used for relationships of distraction index (DI) with radiography, CT, and cartilage variables. RESULTS: Significant relationships included PennHIP osteoarthritis score with cartilage score, CEA, HTEA, DASA, AI, CPC, and TCT; OFA confirmation score with cartilage score, NA, RPC, CEA, HTEA, DASA, AI, CPC, and TCT; cartilage score with NA, RPC, CEA, HTEA, DASA, HASA, AI, and TCT; and DI with cartilage score, CEA, HTEA, DASA, HASA, AI, and CPC. CONCLUSIONS AND CLINICAL RELEVANCE: CT appeared to be a valuable imaging modality for predicting cartilage microdamage in canine hip joints.     

Measurement of Femoral Torsion in Dogs Using a Biplanar Method

The authors defined the concept of femoral torsion using three axes and two planes. Two techniques were used to measure the femoral anteversion angle on 30 femurs of 15 adult mixed breed dogs. The conventional fluoroscopic technique was compared to the right angle triangle technique. The mean angle for each technique was 30.80 and 31.31 degrees, respectively. The right angle triangle technique, using conventional radiographs, appeared as reliable, accurate, and reproducible as the fluoroscopic method and is recommended for clinical use.