THORACIC COMPUTED TOMOGRAPHY IN FELINE PATIENTS WITHOUT USE OF CHEMICAL RESTRAINT

Computed tomography (CT) and thoracic radiography were performed in nonsedated, nonanesthetized, cats with thoracic disease. The final diagnosis was obtained with echocardiography, cytology, histopathology, necropsy, or response to therapy. For CT imaging, cats were in a positioning device using a 16 multislice helical CT system. Fifty‐four cats had CT imaging of which 50 had thoracic radiography. The most common diagnoses were lung neoplasia, lower airway disease, and cardiomyopathy (nine each). Other disease groups included mediastinal mass (eight), infection (seven), trauma (four), and hernia (three). CT provided additional correct diagnoses in 28% (14/50) and additional information in 74% (37/50) of the cats. Additional correct diagnoses achieved only with CT were most common for cats with lower airway disease. The most common additional findings with CT were lung nodules (n=4), lung masses (n=4), bronchiectasis (n=4), and mediastinal lymphadenopathy (n=3). Survey CT led to a significant different diagnosis or different prognosis in 20 of the 50 cats that were imaged both modalities. Contrast CT was performed in 19 cats, most commonly in cats with lung neoplasia (n=6), a mediastinal mass (n=4) or an infection (n=3), and provided additional correct diagnosis in two cats not achieved with survey CT. Thoracic CT using a positioning device in diseased awake cats is feasible, safe, and clinically useful.     

AN OPTIMIZED PROTOCOL FOR MULTISLICE COMPUTED TOMOGRAPHY OF THE CANINE BRAIN

Computed tomography (CT) is commonly used in veterinary practice to evaluate dogs with suspected brain disease, however contrast resolution limitations and artifacts may reduce visualization of clinically important anatomic features. The purpose of this study was to develop an optimized CT protocol for evaluating the canine brain. The head of a 5‐year‐old Springer Spaniel with no neurological signs was imaged immediately following euthanasia using a 4‐slice CT scanner and 282 protocols. Each protocol used a fixed tube voltage of 120 kVp and 10 cm display field of view. Other acquisition and reconstruction parameters were varied. For each protocol, four selected images of the brain were reconstructed, anonymized and saved in DICOM format. Three board‐certified veterinary radiologists independently reviewed each of the four images for each protocol and recorded a numerical quality score for each image. The protocol yielding the lowest total numerical score was defined as the optimal protocol. There was overall agreement that the optimal protocol was the one with the following parameters: sequential mode, 300 mAs, 1 mm slice thickness, 1 s tube rotation time, medium image reconstruction algorithm and applied beam hardening correction. Sequential imaging provided optimal image resolution. The thin‐sliced images provided a small blur due to partial volume artifacts. A high tube current resulted in a relatively low noise level. Use of a medium frequency image reconstruction algorithm provided optimal contrast resolution for brain tissue. Use of a proprietary beam hardening correction filter (Posterior Fossa Optimization) markedly reduced beam‐hardening artifact.     

COMPUTED TOMOGRAPHIC CHARACTERISTICS OF THE THYROID GLANDS IN EIGHT HYPERTHYROID CATS PRE‐ AND POSTMETHIMAZOLE TREATMENT COMPARED WITH SEVEN EUTHYROID CATS

Hyperthyroidism is the most common feline endocrinopathy; thyroid computed tomography (CT) may improve disease detection and methimazole dose selection. Objectives of this experimental pre‐post with historical case‐control study were to perform thyroid CT imaging in awake or mildly sedated hyperthyroid cats, compare thyroid gland CT appearance in euthyroid and hyperthyroid cats pre‐ and postmethimazole treatment, and determine whether thyroid size or attenuation correlate with methimazole dose needed for euthyroidism. Premethimazole treatment, eight hyperthyroid cats received CT scans from the head to heart, which were compared to CT of seven euthyroid cats. Total thyroxine levels were monitored every 3–4 weeks. Postmethimazole CT was performed 30 days after achieving euthyroid status. Computed tomography parameters recorded included thyroid length, width, height, attenuation, and heterogeneity. Median time between CT was 70 days (53–213 days). Mild sedation was needed in five hyperthyroid cats premethimazole, and none postmethimazole. Thyroid volume was significantly larger in hyperthyroid cats compared to euthyroid cats (785.0 mm³ vs. 154.9 mm³; P = 0.002) and remained unchanged by methimazole treatment (?4.5 mm3; P = 0.50). Thyroid attenuation and heterogeneity decreased with methimazole treatment (96.1 HU vs. 85.9 HU; P = 0.02. 12.4 HU vs. 8.1 HU; P = 0.009). Methimazole dose ranged from 2.5 to 10 mg daily with a positive correlation between pretreatment thyroid gland volume and dose needed to achieve euthyroidism (P = 0.03). Euthyroid and hyperthyroid cats are easily imaged awake or mildly sedated with CT. Methimazole in hyperthyroid cats significantly lowers thyroid attenuation and heterogeneity, but not size.     

Thoracic high resolution CT using the modified VetMousetrap™ device is a feasible method for diagnosing canine idiopathic pulmonary fibrosis in awake West Highland White Terriers

Canine idiopathic pulmonary fibrosis is a chronic, progressive interstitial lung disease particularly prevalent in West Highland White Terriers. In the present prospective pilot study, we evaluated the feasibility of modified VetMousetrap? device in high resolution CT to detect idiopathic pulmonary fibrosis in West Highland White Terriers. Twelve awake West Highland White Terriers with canine idiopathic pulmonary fibrosis and 24 clinically healthy West Highland White Terriers were scanned using a helical dual slice scanner utilizing VetMousetrap? device without or with minimal chemical restraint with butorphanol. Three evaluators blindly assessed the images for image quality and the presence of canine idiopathic pulmonary fibrosis related imaging findings such as ground glass opacity and reticular opacities. Additionally, the attenuation of the lung was quantified with ImageJ software using histogram analysis of density over the lung fields. Computed tomography was successfully completed and motion artifact ranked in statistical analysis barely noticeable to mild in all dogs. The agreement between imaging findings and clinical status was very good with overall κ value 0.91 and percentage of agreement of 94%. There was also very good intraobserver (κ_range = 0.79‐0.91) and interobserver agreement (κ = 0.94). Moderate to severe ground glass opacity was present in all affected dogs. In the ImageJ analysis, a significant difference in lung attenuation between the study groups was observed. We conclude that modified VetMousetrap? device is applicable in diagnosing canine idiopathic pulmonary fibrosis in awake West Highland White Terriers avoiding anesthetic risk in these often severely hypoxic patients.     

Optimization of contrast-enhanced multidetector abdominal computed tomography in sedated canine patients

A major disadvantage of computed tomography for abdominal screening in dogs has been the need for general anesthesia to prevent motion artifacts. With multidetector helical CT, it is possible to decrease examination time, allowing patients to be scanned under sedation. It is also desirable to decrease tube loading to prolong x-ray tube life. To develop a protocol that will allow for examination of sedated patients with minimal image artifacts, milliamperage (mA) and helical pitch were varied, providing 16 experimental scan protocols. A standard clinical protocol was also tested, providing 17 protocols for evaluation. These protocols were tested, using a standard CT phantom, canine tissues in a water bath, and a canine cadaver. The cadaver images were scored semiquantitatively by three reviewers to determine the protocol with the best combination of speed and minimal image artifact. The optimized protocol was then applied to 27 sedated canine patients of three body weight categories. The images obtained were compared to the standard protocol by two reviewers for presence of motion, streak, and quantum mottle artifacts. There was significantly more streak artifact noted by one observer using the optimized study protocol, but no significant difference in any other category. Scanning under sedation was well tolerated in all patients, and sedated CT examination is a promising tool for screening abdominal disease in dogs.     

COMPUTED TOMOGRAPHY OF NONANESTHETIZED CATS WITH UPPER AIRWAY OBSTRUCTION

Upper airway obstruction is a potentially life‐threatening problem in cats and for which a noninvasive, sensitive method rapid diagnosis is needed. The purposes of this prospective study were to describe a computed tomography (CT) technique for nonanesthetized cats with upper airway obstruction, CT characteristics of obstructive diseases, and comparisons between CT findings and findings from other diagnostic tests. Ten cats with clinical signs of upper airway obstruction were recruited for the study. Four cats with no clinical signs of upper airway obstruction were recruited as controls. All cats underwent computed tomography imaging without sedation or anesthesia, using a 16‐slice helical CT scanner and a previously described transparent positional device. Three‐dimensional (3D) internal volume rendering was performed on all CT image sets and 3D external volume rendering was also performed on cats with evidence of mass lesions. Confirmation of upper airway obstruction was based on visual laryngeal examination, endoscopy, fine‐needle aspirate, biopsy, or necropsy. Seven cats were diagnosed with intramural upper airway masses, two with laryngotracheitis, and one with laryngeal paralysis. The CT and 3D volume‐rendered images identified lesions consistent with upper airway disease in all cats. In cats with mass lesions, CT accurately identified the mass and location. Findings from this study supported the use of CT imaging as an effective technique for diagnosing upper airway obstruction in nonanesthetized cats.     

AN OPTIMIZED COMPUTED TOMOGRAPHY PROTOCOL FOR METALLIC GUNSHOT HEAD TRAUMA IN A SEAL MODEL

Computed tomography (CT) is commonly used to assess animals with head trauma. However, strongly attenuating objects such as metallic gunshot cause artifacts that may make accurate localization of shrapnel pieces difficult. The purpose of this study was to develop an optimized CT protocol for minimizing metal artifacts in an animal model of gunshot head trauma. A cadaver head of a stranded Gray seal (Halichoerus grypus) was shot post‐mortem with a 0.223‐inch caliber rifle. The head was frozen, thawed, and scanned using a multislice CT scanner and protocols with varying acquisition and reconstruction parameters. Scans were acquired with and without use of the scanner's proprietary Extended CT Scale (ECTS) mode and beam hardening reduction (Posterior Fossa Optimization [PFO]) filter. Window/level display settings were also varied. For each protocol and each of five selected metallic shrapnel pieces, a single observer measured combined metal halo artifact and shrapnel area using a hand‐traced region of interest. The number of hypo‐ and hyper‐attenuating streak artifacts was also recorded. Measurements were repeated for three different reading sessions. Metal CT artifacts were minimized with a high‐frequency image reconstruction algorithm and a wide window setting. Further artifact reduction was achieved with a proprietary ECTS raw data reconstruction technique and a very wide window. This enabled a more confident evaluation of surrounding bone. On the other hand, these techniques are unfortunately not effective under conditions of soft tissue evaluation. Increasing tube voltage and use of a proprietary PFO filter did not yield a significant reduction in metal artifacts.     

CLINICAL APPLICATION OF PATLAK PLOT CT‐GFR IN ANIMALS WITH UPPER URINARY TRACT DISEASE

Glomerular filtration rate (GFR), an important parameter of renal function, is difficult to assess clinically. Serum creatinine and blood urea nitrogen measurements lack sensitivity, whereas radionuclide determination of GFR is not always available and requires postinjection patient isolation. GFR can be determined using computed tomography (CT), most commonly via Patlak plot analysis. Four adult cats, two adult dogs, and a foal underwent abdominal CT under general anesthesia for various diseases of the upper urinary tract. CT‐GFR was measured with a single‐slice dynamic acquisition and Patlak plot analysis. In five animals, the total CT‐GFR appeared to be below normal, corresponding with mild (two animals) and moderate (two animals) increases of serum creatinine in four. In the two animals with normal or increased CT‐GFR, serum creatinine was within the reference values. A significant negative logarithmic relationship was found between CT‐GFR and serum creatinine values (P=0.008; r²=0.75). No complications occurred during or following CT‐GFR. CT examination provided clinically relevant information in 3/5 patients with possible ureteral obstruction and in 3/3 patients with suspected ureteral calculi. Single‐slice dynamic CT‐GFR was practical and provided clinically useful information in this small series of patients undergoing CT of the upper urinary tract. There was a significant relationship between CT‐GFR and serum creatinine values, which supports the clinical potential of CT‐GFR and justifies further investigation of this technique.     

WHOLE‐BODY BIODISTRIBUTION OF 3′‐DEOXY‐3′‐[18F]FLUOROTHYMIDINE (18FLT) IN HEALTHY ADULT CATS

Positron emission tomography/computed tomography (PET/CT) utilizing 3′‐deoxy‐3′‐[¹⁸F]fluorothymidine (¹⁸FLT), a proliferation tracer, has been found to be a useful tool for characterizing neoplastic diseases and bone marrow function in humans. As PET and PET/CT imaging become increasingly available in veterinary medicine, knowledge of radiopharmaceutical biodistribution in veterinary species is needed for lesion interpretation in the clinical setting. The purpose of this study was to describe the normal biodistribution of ¹⁸FLT in adult domestic cats. Imaging of six healthy young adult castrated male cats was performed using a commercially available PET/CT scanner consisting of a 64‐slice helical CT scanner with an integrated whole‐body, high‐resolution lutetium oxy‐orthosilicate (LSO) PET scanner. Cats were sedated and injected intravenously with 108.60 ± 2.09 (mean ± SD) MBq of ¹⁸FLT (greater than 99% radiochemical purity by high‐performance liquid chromatography). Imaging was performed in sternal recumbency under general anesthesia. Static images utilizing multiple bed positions were acquired 80.83 ± 7.52 (mean ± SD) minutes post‐injection. Regions of interest were manually drawn over major parenchymal organs and selected areas of bone marrow and increased tracer uptake. Standardized uptake values were calculated. Notable areas of uptake included hematopoietic bone marrow, intestinal tract, and the urinary and hepatobiliary systems. No appreciable uptake was observed within brain, lung, myocardium, spleen, or skeletal muscle. Findings from this study can be used as baseline data for future studies of diseases in cats.     

SUSCEPTIBILITY ARTIFACTS ON T2*‐WEIGHTED MAGNETIC RESONANCE IMAGING OF THE CANINE AND FELINE SPINE

The T2*‐weighted gradient recalled echo sequence is a sensitive means to detect blood degradation products. While not a routine sequence in magnetic resonance imaging of the spine in small animals, it can provide additional valuable information in select cases. The goal of this retrospective, cross‐sectional study was to describe findings when acquiring this sequence during magnetic resonance imaging examination of the spine in small animals. The University of Tennessee's veterinary radiology database was searched for dogs and cats that underwent magnetic resonance imaging for suspect spinal disease in which a T2*‐weighted gradient recalled echo sequence was acquired and susceptibility artifact was identified. The following information was recorded: signalment, clinical signs, location and appearance of susceptibility artifact, and final diagnosis. Thirty‐nine cases were included in the study. Extradural susceptibility artifacts were observed in cases of intervertebral disc herniation with or without associated hemorrhage (n = 28), extradural hemorrhage associated with spinal trauma (n = 2), hemophilia (n = 1), and in a cystic extradural mass (n = 1). Remaining lesions displaying susceptibility artifact were intramedullary and included presumptive acute noncompressive nucleus pulposus extrusion (n = 2), hematoma (n = 1), hemangiosarcoma metastasis (n = 1), intramedullary disc extrusion (n = 1), presumptive meningomyelitis (n = 1), and a mass of undetermined etiology (n = 1). Inclusion of a T2*‐weighted gradient recalled echo sequence may be helpful in spinal magnetic resonance imaging when standard imaging sequences are ambiguous or intramedullary lesions are observed.     

COMPUTED TOMOGRAPHIC FEATURES OF LUNG LOBE TORSION

The imaging features of lung lobe torsion in 10 dogs (nine complete, one partial torsion) acquired with a helical single‐slice computed tomography (CT) unit are described. Attenuation values of normal, rotated, and adjacent collapsed lung lobes before and after intravenous contrast medium administration were compared. Affected lung lobes were: left cranial (5), right middle (3), right cranial (1), and left caudal (1). CT findings in nine dogs with complete lung lobe torsion included pleural effusion and an abruptly ending bronchus. In eight of these dogs, enlargement, consolidation, emphysema of the affected lung lobe, and mediastinal shift to the contralateral side were present. Rotated lung lobes did not enhance, whereas adjacent collapsed and aerated lung lobes did (P<0.05). Apnea induced with hyperventilation or breath‐hold is essential to reduce motion artefacts and obtain a diagnostic study.     

EVALUATION OF QUANTITATIVE THYROID SCINTIGRAPHY FOR DIAGNOSIS AND STAGING OF DISEASE SEVERITY IN CATS WITH HYPERTHYROIDISM: COMPARISON OF THE PERCENT THYROIDAL UPTAKE OF PERTECHNETATE TO THYROID‐TO‐SALIVARY RATIO AND THYROID‐TO‐BACKGROUND RATIOS

Thyroid scintigraphy is commonly used for evaluation of cats with hyperthyroidism, with the thyroid‐to‐salivary ratio (T/S) being the most common method to quantify the degree of thyroid activity and disease. Calculation of thyroid‐to‐background ratios (T/B) or percent thyroidal uptake of ^99mTcO^?₄ (TcTU) has only been reported in a few studies. The purpose of this prospective, cross‐sectional study was to evaluate a number of quantitative scintigraphic indices as diagnostic tests for hyperthyroidism, including the T/S, three different T/B, TcTU, and estimated thyroid volume. Of 524 cats referred to our clinic for evaluation of suspected hyperthyroidism, the diagnosis was confirmed (n = 504) or excluded (n = 20) based on results of a serum thyroid panel consisting of thyroxine (T₄), triiodothyronine (T₃), free T₄ (fT₄), and thyroid‐stimulating hormone (TSH) concentrations. In the hyperthyroid cats, median values for TcTU, T/S, and three T/B ratios were all significantly higher (P < 0.001) than values in euthyroid suspect cats or clinically normal cats. All scintigraphic parameters were relatively sensitive and specific as diagnostic tests for hyperthyroidism, but the T/S ratio had the highest test accuracy. The T/S ratio correlated strongly with the TcTU (r = 0.85). However, the TcTU had a higher and more significant correlation (P < 0.01) with serum T₄ (r = 0.76 vs. 0.64), T₃ (r = 0.77 vs. 0.64), and estimated thyroid volume (r = 0.62 vs. 0.38). Overall, calculation of TcTU is an accurate diagnostic test, but also appears to be the best parameter to predict the functional volume and metabolic activity of the feline adenomatous thyroid gland.     

Thick-section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horses

Computed tomography (CT) of the caudal fossa of 10 canine and nine equine cadaver heads was performed with conventional slice widths of 5 and 10 mm, respectively, and with thin collimations of 1 and 2 mm, respectively. Reformatting of thinly collimated slices was done by addition of thinly collimated slices to section thicknesses of 5 and 10 mm, respectively. Seventy-six pairs of conventional and reformatted images of identical anatomic locations were evaluated for magnitude of skull-base-related artifacts and image noise. A film-based subjective evaluation of artifact and noise was performed by four radiologists on a five-point score system. There was a statistically significant reduction of artifacts of canine and equine heads by 33% and 50%, respectively, on reformatted images compared with conventional ones but no difference in image noise. On objective artifact assessment based on the magnitude of standard deviation of attenuation values in the interpetrosal region, there was a statistically significant reduction of artifacts of canine and equine heads by 23% and 39%, respectively, on reformatted images. Thick-section reformatting significantly improves image quality of CT scans of the caudal fossa in dogs and horses.     

MAGNETIC RESONANCE IMAGING OF THE CANINE BRAIN AT 7 T

The purpose of this study was to describe relevant canine brain structures as seen on T2-weighted images following magnetic resonance (MR) imaging at 7 T and to compare the results with imaging at 1.5 T. Imaging was performed on five healthy laboratory beagle dogs using 1.5 and 7 T clinical scanners. At 1.5 T, spin echo images were acquired, while gradient echo images were acquired at 3 T. Image quality and conspicuity of anatomic structures were evaluated qualitatively by direct comparison of the images obtained from the two different magnetic fields. The signal-to-nose ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared between 1.5 and 7 T. The T2-weighted images at 7 T provided good spatial and contrast resolution for the identification of clinically relevant brain anatomy; these images provided better delineation and conspicuity of the brain stem and cerebellar structures, which were difficult to unequivocally identify at 1.5 T. However, frontal and parietal lobe and the trigeminal nerve were difficult to identify at 7 T due to susceptibility artifact. The SNR and CNR of the images at 7 T were significantly increased up to 318% and 715% compared with the 1.5 T images. If some disadvantages of 7 T imaging, such as susceptibility artifacts, technical difficulties, and high cost, can be improved, 7 T clinical MR imaging could provide a good experimental and diagnostic tool for the evaluation of canine brain disorders.     

X‐RAY ATTENUATION OF THE LIVER AND KIDNEY IN CATS CONSIDERED AT VARYING RISK OF HEPATIC LIPIDOSIS

X‐ray attenuation of the liver has been measured using computed tomography (CT) and reported to decrease in cats with experimentally induced hepatic lipidosis. To assess the clinical utility of this technique, medical records and noncontrast CT scans of a series of cats were retrospectively reviewed. A total of 112 cats met inclusion criteria and were stratified into three hepatic lipidosis risk groups. Group 1 cats were considered low‐risk based on no history of inappetence or weight loss, and normal serum chemistry values; Group 2 cats were considered intermediate risk based on weight loss, serum hepatic enzymes above normal limits, or reasonably controlled diabetes mellitus; and Group 3 cats were considered high risk based on poorly controlled diabetes mellitus due to hypersomatotropism. Mean CT attenuation values (Hounsfield units, HU) were measured using regions of interest placed within the liver and cranial pole of the right kidney. Hepatic and renal attenuation were weakly positively correlated with each other (r = 0.2, P = 0.03) and weakly negatively correlated with body weight (r = ?0.21, P = 0.05, and r = ?0.34, P = 0.001, respectively). Mean (SD) hepatic and renal cortical attenuation values were 70.7 (8.7) HU and 49.6 (9.2) HU for Group 1 cats, 71.4 (7.9) HU and 48.6 (9.1) HU for Group 2, and 68.9 (7.6) HU and 47.6 (7.2) HU for Group 3. There were no significant differences in hepatic or renal attenuation among groups. Findings indicated that CT measures of X‐ray attenuation in the liver and kidney may not be accurate predictors of naturally occurring hepatic lipidosis in cats.     

COMPARISON BETWEEN COMPUTED TOMOGRAPHY AND 99m TC‐ PERTECHNETATE SCINTIGRAPHY CHARACTERISTICS OF THE THYROID GLAND IN CATS WITH HYPERTHYROIDISM

Scintigraphy is currently the reference standard for diagnosing feline hyperthyroidism; however, computed tomography (CT) is more widely available in veterinary practice. The purposes of this prospective study were to describe the CT appearance of thyroid glands in cats with hyperthyroidism and compare CT findings with findings from ^99mTc–pertechnetate scintigraphy. Twenty‐five adult hyperthyroid cats were included. Plain CT images were acquired for each cat and the following characteristics recorded for each thyroid lobe: visibility, delineation, position, attenuation, shape, and subjective size. Scintigraphic images were also acquired and the following characteristics recorded: radiopharmaceutical uptake, delineation, ectopic foci, shape, and subjective size. In CT images, thyroid lobes were most commonly found between the second and fourth cervical vertebrae, dorsolateral to the trachea. Affected thyroid lobes (based on scintigraphy reference standard) were most commonly oval and moderately enlarged in CT images. A heterogeneous attenuation pattern (isoattenuating to adjacent soft tissues with hypo‐ and hyperattenuating foci) was most commonly found in affected thyroid lobes. A positive correlation (P < 0.01) was identified between CT and scintigraphy for left‐to‐right thyroid lobe size relationship and subjective size of the larger thyroid lobe. The CT estimated mass was significantly higher (median = 148.8; range = [0;357.6]) for the more active thyroid lobe compared to the less active thyroid lobe (median = 84.6; range = [0;312.3]); (W = 154; P < 0.01). Findings indicated that CT may not reliably differentiate unilateral vs. bilateral hyperthyroidism in cats; however, CT may be a reliable alternative test for correctly identifying the more active thyroid lobe.     

COMPARISON OF MAGNETIC RESONANCE IMAGING,COMPUTED TOMOGRAPHY,AND RADIOGRAPHY FOR ASSESSMENT OF NONCARTILAGINOUS CHANGES IN EQUINE METACARPOPHALANGEAL OSTEOARTHRITIS

We compared the ability of 1.5 T magnetic resonance imaging (MRI), computed tomography (CT), and computed radiography (CR) to evaluate noncartilaginous structures of the equine metacarpophalangeal joint (MCP), and the association of imaging changes with gross cartilage damage in the context of osteoarthritis. Four CR projections, helical single‐slice CT, and MRI (T1‐weighted gradient recalled echo [GRE], T2^*‐weighted GRE with fast imaging employing steady‐state acquisition [FIESTA], T2‐weighted fast spin echo with fat saturation, and spoiled gradient recalled echo with fat saturation [SPGR‐FS]) were performed on 20 racehorse cadaver forelimbs. Osteophytosis, synovial effusion, subchondral bone lysis and sclerosis, supracondylar lysis, joint fragments, bone marrow lesions, and collateral desmopathy were assessed with each modality. Interexaminer agreement was inferior to intraexaminer agreement and was generally moderate (i.e., 0.4<κ<0.6). Subchondral bone sclerosis scores using CT or MRI were correlated significantly with the reference quantitative CT technique used to assess bone mineral density (P<0.0001). Scores for subchondral lysis and osteophytosis were higher with MRI or CT vs. CR (P<0.0001). Although differences between modalities were noted, osteophytosis, subchondral sclerosis, and lysis as well as synovial effusion were all associated with the degree of cartilage damage and should be further evaluated as potential criteria to be included in a whole‐organ scoring system. This study highlights the capacity of MRI to evaluate noncartilaginous changes in the osteoarthritic equine MCP joint.     

RADIOGRAPHIC DIAGNOSIS OF MECHANICAL OBSTRUCTION IN DOGS BASED ON RELATIVE SMALL INTESTINAL EXTERNAL DIAMETERS

Mechanical obstruction is a frequent cause of acute vomiting in dogs requiring prompt diagnosis to improve patient management and prognosis. The purpose of this retrospective study was to compare small intestinal radiographic characteristics in dogs with versus without mechanical intestinal obstruction. Fifty dogs with gastrointestinal clinical signs and abdominal radiographs were recruited from hospital record archives and assigned to groups (group 1, obstructive, n = 25; group 2, nonobstructive n = 25). Abdominal radiographs were randomized and independently interpreted by three examiners who were unaware of group status. Intestinal dilation was subjectively scored based on distribution (segmental, regional or diffuse), and severity (absent, mild, moderate or severe). Small intestinal maximal diameter (SI_max), L5 vertebral body height, small intestinal minimal diameter (SI_min), and an estimated average of small intestinal diameters (SI_ave) were measured and three ratios were calculated: SI_max/L5, SI_max/SI_min, and SI_max/SI_ave. Segmental dilation was more prevalent in obstructed dogs for all examiners (P ≤ 0.03) and most nonobstructed dogs had no dilation (P ≤ 0.05). All ratios were higher in obstructed dogs (P < 0.002). Subjective dilation scores and ratio measurements had low interobserver agreement (absent to fair, with kappa values between ?0.06 and 0.57) and reproducibility (coefficients of 0.35–0.61). Findings indicated that dogs with SI_max/L5 ≤ 1.4, SI_max/SI_min ≤ 2, and SI_max/SI_ave ≤ 1.3 values are very unlikely to be mechanically obstructed; dogs with SI_max/L5 ≥ 2.4, SI_max/SI_min ≥ 3.4 and SI_max/SI_ave ≥ 1.9 are very likely obstructed, particularly if segmental dilation (less than 25% of the small intestine) is present. Dogs with ratios falling between these thresholds may need further testing unless other signs justify surgical exploration or endoscopy.     

TECHNICAL PARAMETERS AFFECTING IMAGE CHARACTERISTICS IN IN VIVO MR MICROSCOPY OF THE MOUSE

The aim of the study was to assess the effects of changing acquisition parameters used for high-resolution in vivo magnetic resonance (MR) microscopy on image quality and scan time. The head or abdomen of 11 normal and 1 glioblastoma-bearing anesthetized BALB/c mice were imaged using a high-resolution 7.0-Tesla magnet. Scan parameters such as matrix size (MTX), slice thickness (ST), number of excitations (NEX), pulse sequence type including repetition time (TR) and echo time (TE), respiratory gating, and intraperitoneal contrast medium administration were altered to assess their actual effect on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) as compared to calculated effects. As expected, SNR increased with increasing ST or NEX and with decreasing MTX. However, although the empirical increase in SNR was similar to that expected for increased ST, it was less than that anticipated for increasing NEX or decreasing MTX. Increasing NEX and applying respiratory gating both increased SNR and reduced the image degradation associated with respiratory motion in images of the abdomen. Intraperitoneal contrast medium administration produced a marked increase in CNR in the subject with the implanted glioblastoma, suggesting that this route is satisfactory for the enhancement of lesions disrupting the blood-brain barrier. The consequence of improving image quality in terms of spatial and contrast resolution is increased scan time. However, the actual increase in SNR when altering acquisition parameters may not be as much as predicted by theory.