MAGNETIC RESONANCE IMAGING IN FOALS WITH INFECTIOUS ARTHRITIS

The magnetic resonance (MR) imaging findings of foals with infectious and noninfectious arthritis are described. Six foals with infectious arthritis and three foals with noninfectious arthritis were grouped based on synovial fluid analysis results and examined with radiography and MR imaging. Four out of six foals with infectious arthritis had osseous lesions in MR images indicative of osteomyelitis and only 4/19 lesions were detected on digital radiographs. The three foals with noninfectious arthritis had no osseous lesions in MR images or radiographically. Of the six joints that had osseous lesions detected with MR imaging, three had at least one lytic lesion detected radiographically. Osseous lesions in the epiphysis, metaphysis, and physis appeared in MR images as T2W, short tau inversion recovery, and proton density hyperintense foci with a hypointense halo. The same lesions appeared hyperintense in the 3D RSSG water excitation pulse sequence but lacked a surrounding hypointense halo. Most joints of foals with infectious arthritis had heterogenous signals within the synovial fluid whereas all of the nonseptic joints had homogenous synovial fluid signals. MR imaging appears to be better than radiography in the detection of osseous lesions in foals diagnosed with infectious arthritis and may be a valuable screening test for the presence of osteomyelitis.     

CLINICAL USE OF 99mTC-MDP SCINTIGRAPHY IN THE EQUINE MANDIBLE AND MAXILLA

^99mTc-methylene diphosphonate (MDP) radionuclide imaging examinations were done in four horses having clinical evidence of skull trauma or infection. Radiographs were made of each horse prior to scintigraphy. Four case histories are presented. In each instance, scintigraphy provided complementary information to that obtainable through radiography, which aided in accurately localizing and characterizing the site and extent of abnormalities, and which proved particularly valuable as an aid for therapeutic planning.     

Biochemical markers of bone metabolism in animals: uses and limitations

Routine assessment of the skeleton's response to disease and injury traditionally has consisted of plain-film radiography supplemented with advanced imaging techniques, such as computed tomography, magnetic resonance imaging, nuclear scintigraphy, and bone densitometry. Although these techniques provide increased sensitivity as compared with radiography, they still are limited by the fact that they can only document the net results of past skeletal activity. In contrast, serum and urinary biomarkers of bone formation and resorption provide near real-time information about bone cell activity. In this review, I describe the scientific rationale behind the use of these markers in humans and detail the efforts that have been made to adapt this technology to veterinary medicine and animal research. Commercial assay kits that are applicable to different animal species are described, and the potential limitations of the technology are discussed. The goal of this review is to provide clinical pathologists and researchers with the information needed to decide whether the use of bone markers is likely to be helpful and to select the most appropriate marker (or panel of markers) to answer a particular question.     

Standing low‐field magnetic resonance imaging of a comminuted central tarsal bone fracture in a horse

This report describes the use of low‐field standing magnetic resonance imaging (MRI) in the diagnosis and clinical decision making process in a 14‐year‐old Dutch Warmblood mare with a comminuted central tarsal bone fracture. Magnetic resonance imaging in the standing horse was preferred over computed tomography examination under general anaesthesia because the animal had sustained the injury during a poor recovery from a previous general anaesthetic episode. Magnetic resonance imaging examination identified a comminuted central tarsal bone fracture with a configuration that was not identifiable with radiography. Due to extensive comminution of this fracture, conservative management was pursued. Standing low‐field MRI examination enabled safe examination of this animal and provided useful diagnostic information whilst facilitating the clinical decision making process.     

IMAGING: RADIOGRAPHY—1

This is the first article in a series on imaging. An overview of principles involved in imaging by survey radiography, contrast radiography, and fluoroscopy is presented. Anatomic and functional information available by these imaging modes are compared. Survey radiography is convenient and relatively inexpensive but often provides limited anatomic and functional information. Contrast radiography often increases anatomic information and, when used with sequential exposures, enhances functional assessment of various organs. Fluoroscopy provides a continuous but non-permanent image used in evaluation of organ motion or as a localizing tool. Permanent records are obtained by spot radiographs, spot film cameras, cine fluorography, and/or video tape/ disc systems.     

Ancillary diagnostic imaging. Angiography, ultrasonography, scintigraphy, and xeroradiography

Veterinary medical imaging is now accepted as including a number of imaging modalities other than conventional radiography. Although the wide availability and relatively low cost of conventional radiography will keep it in the forefront of veterinary medical imaging, other imaging modalities or techniques such as those discussed in this article will, where available, be of significant value in selected cases of bovine lameness.     

Comparison of radiography and magnetic resonance imaging for evaluating the extent of nasal neoplasia in dogs

OBJECTIVES: Magnetic resonance imaging (MRI) is increasingly used in veterinary practice and, in some centres, is part of the diagnostic work-up of small animals with nasal disease. However, there are no published studies which critically evaluate the use of magnetic resonance imaging for this purpose. The purpose of this work was to assess the changes seen using magnetic resonance imaging and to compare them with radiography. METHODS: The study included 12 dogs that had undergone both radiography and magnetic resonance imaging of the nasal cavity and had a histopathological diagnosis of malignant nasal neoplasia. Two pairs of board-certified radiologists scored the radiographs and the MRI scans, evaluating 10 signs of abnormality using a simple scoring system. Magnetic resonance imaging features were described in detail, and radiographic and magnetic resonance imaging scores for each sign as well as total scores were compared. RESULTS: Magnetic resonance imaging often showed that the tumour was more extensive than it had appeared on radiography but occasionally showed that radiographs had overestimated its size. Although radiography was reliable for assessment of the presence and size of a mass and for the extent of turbinate destruction, it usually failed to show occlusion of the major airway passages that were evident on magnetic resonance imaging. Extension of the tumour into the opposite nasal cavity, frontal sinus, orbit and cranial cavity was shown much better on magnetic resonance imaging. CLINICAL SIGNIFICANCE: Minor but significant extension beyond the nasal cavity, which is important for treatment planning and prognosis, requires magnetic resonance imaging for demonstration, although radiography shows major changes reliably.     

A COMPARISON OF RADIOGRAPHY, COMPUTED TOMOGRAPHY, AND MAGNETIC RESONANCE IMAGING FOR THE DIAGNOSIS OF PALMAR PROCESS FRACTURES IN FOALS

The relative sensitivity of radiography, computed tomography, and magnetic resonance imaging for detecting palmar process fractures of the distal phalanx in foals was determined and the imaging findings were compared with histomorphologic evaluations of the palmar processes. Compared to radiography, computed tomography and magnetic resonance imaging did not improve the sensitivity for detection of palmar process fractures. Statistical agreement for palmar process fracture diagnosis was excellent among the three imaging modalities. Histomorphologic evaluations were more sensitive for diagnosis of palmar process fracture than any of the imaging modalities. Three-dimensional image reconstructions and volume measurements of distal phalanges and palmar process fracture fragments from computed tomography studies provided more complete anatomical information than radiography. Magnetic resonance imaging confirmed that the deep digital flexor tendon insertion on the distal phalanx is immediately axial to the site where palmar process fractures occur, and differentiated cartilage, bone, and soft tissue structures of the hoof.     

Computed tomography of proximal metatarsal and concurrent third tarsal bone fractures in a Thoroughbred racehorse

A 2‐year‐old Thoroughbred filly presented to the William R. Pritchard Veterinary Medical Teaching Hospital at the University of California at Davis for whole body nuclear scintigraphic evaluation after an acute onset of nonweightbearing right hindlimb lameness post race. The use of computed tomography (CT) enabled visualisation of additional pathology that was not initially appreciable using combined imaging modalities of nuclear scintigraphy and digital radiography, which ultimately altered the selected course of treatment. Computed tomography in horses with fractures of the cuboidal bones of the hock can provide valuable additional information regarding fracture configuration and radiographically occult pathology, which may help to guide clinical decisions about treatment.     

Advanced imaging of an incomplete fracture and exostosis of the third metacarpal bone in a young Warmblood horse

A 5-year-old Hanoverian gelding with acute moderate right forelimb lameness underwent nuclear scintigraphy, which identified marked increase in radiopharmaceutical uptake of the proximomedial aspect of the right metacarpus. Ultrasonography and radiography identified sclerosis and exostosis of the proximomedial aspect of the metacarpal bone III in-between the suspensory ligament and the second metacarpal bone, and presence of a suspected fracture. The owner requested euthanasia of the gelding, and post-mortem computed tomography and magnetic resonance imaging identified marked bone sclerosis and thickening of the palmar cortex of the metacarpal III (McIII), presence of an incomplete fracture in the palmar cortex of McIII and expansive exostosis from McIII extending in a palmar direction between the suspensory ligament and the second metacarpal bone. Histopathological examination confirmed the imaging findings of sclerosis and led to final diagnosis of a fracture of the palmar cortex of the McIII associated with an exostosis encroaching the medial aspect of the suspensory ligament. No abnormalities were present in the suspensory ligament or metacarpal bone II (McII).     

EX VIVO MAGNETIC RESONANCE IMAGING OF THE DISTAL ROW OF EQUINE CARPAL BONES: ASSESSMENT OF BONE SCLEROSIS AND CARTILAGE DAMAGE

The distal row of carpal bones (C2, C3, and C4) from eight left intercarpal joints--four from Standardbred Trotters and four from Swedish Warmblood horses--were used to assess the potential of magnetic resonance (MR) imaging to detect cartilage and bone lesions. The joints used in the study were classified by macroscopic and radiographic examinations as having normal, mild, moderate, or severe articular cartilage lesions and bone sclerosis. Those classifications correlated well with the appearance of the MR images. Bone sclerosis in the MR images was observed as regions of decreased signal intensity. Upon quantitative analysis of the MR images there was a significant difference (p < 0.0001) in the MR signal intensity from areas where radiographic bone sclerosis was observed compared to areas of radiographic nonsclerotic bone. In addition, the MR images were used to pilot the location of histology slices through areas of interest that were then examined microscopically; hence, the lesions found from the MR imaging examination were verified microscopically. It was concluded that cartilage lesions and cartilage loss are related to the sclerotic state of the underlying bone. The MR protocols developed in this study were applied on five intact cadaveric carpal joints, and it was concluded that MR imaging could successfully be used in the intact joint to detect minor cartilage and bone lesions not visualized by either radiography or macroscopic examination. Hence, MR imaging can be used to delineate interactions between articular cartilage and subchondral bone over time and in vivo.     

REVIEW OF DIAGNOSTIC IMAGING OF EAR DISEASES IN THE DOG AND CAT

Diagnostic imaging techniques (conventional radiography, computed tomography and magnetic resonance imaging) are an essential tool in the diagnostic work-up of ear diseases. Conventional radiography is commonly used, but often lacks sensitivity. Computed tomography (CT) and magnetic resonance (MR) are complementary imaging studies of the middle ear, labyrinth, internal auditory canal and their contents. CT provides excellent images of bony structures and is indicated where osseous changes are of greatest diagnostic importance. MR is superior in imaging soft tissue components including intralabyrinthine fluid. Therefore, more than one of these imaging techniques may be required in order to make a diagnosis.     

Comparison of computed radiography and conventional radiography in detection of small volume pneumoperitoneum

The role of digital imaging is increasing as these systems are becoming more affordable and accessible. Advantages of computed radiography compared with conventional film/screen combinations include improved contrast resolution and postprocessing capabilities. Computed radiography's spatial resolution is inferior to conventional radiography; however, this limitation is considered clinically insignificant. This study prospectively compared digital imaging and conventional radiography in detecting small volume pneumoperitoneum. Twenty cadaver dogs (15-30 kg) were injected with 0.25, 0.25, and 0.5 ml for 1 ml total of air intra-abdominally, and radiographed sequentially using computed and conventional radiographic technologies. Three radiologists independently evaluated the images, and receiver operating curve (ROC) analysis compared the two imaging modalities. There was no statistical difference between computed and conventional radiography in detecting free abdominal air, but overall computed radiography was relatively more sensitive based on ROC analysis. Computed radiographic images consistently and significantly demonstrated a minimal amount of 0.5 ml of free air based on ROC analysis. However, no minimal air amount was consistently or significantly detected with conventional film. Readers were more likely to detect free air on lateral computed images than the other projections, with no significant increased sensitivity between film/screen projections. Further studies are indicated to determine the differences or lack thereof between various digital imaging systems and conventional film/screen systems.     

ENLARGING BILATERAL FEMORAL CONDYLAR BONE CYSTS WITHOUT SCINTIGRAPHIC UPTAKE IN A YEARLING FOAL

Bilateral subchondral bone cysts of the femoral condyles were diagnosed by conventional radiography in a 14 month old Appaloosa colt. Surgical debridement was performed, and over the next 18 months the appearance of the cysts was evaluated with radiography and bone scintigraphy. On the preoperative scintigrams, increased radiopharmaceutical uptake was associated with the cysts. Despite continued radiographic enlargement, the cysts did not demonstrate increased radiopharmaceutical uptake post-operatively.     

IMAGING: RADIOGRAPHY-11*

In this paper an overview of principles involved in radiographic imaging by tomography, magnification radiography, xeroradiography, and computed tomography is presented. Tomography is a method to selectively blur distracting superimposed shadows while maintaining relative image sharpness in a plane of concern. Magnification radiography is a method to directly enlarge the radiographic image by increasing object-film distance and utilizing a small focal spot. Xeroradiography is an electrostatic imaging process that provides wide latitude and good resolution through enhanced contrast in tissues with poor inherent contrast. Computed tomography involves imaging by computer analysis of x-ray absorption utilizing rotational x-ray projections.     

Nuclear medical bone imaging and targeted radiography for evaluation of skeletal neoplasms in 23 dogs

Nuclear medical bone imaging was used in combination with targeted radiography to detect metastatic or multicentric lesions in 23 dogs with skeletal neoplasms. Each dog with a radiographically diagnosed skeletal neoplasm was injected with Technetium-99m labeled methylene diphosphonate (99mTc-MDP) (15.0 mCi intravenously) for whole body imaging. All areas with increased uptake of 99mTc-MDP were radiographed. In 19 dogs, the amount of bone shaft involvement in primary sites indicated by bone imaging was larger than the amount indicated by radiography. Eighteen dogs had secondary areas of increased 99mTc-MDP uptake, six of which had secondary areas that were suspected radiographically to be neoplastic. Four dogs had lesions characterized histologically as neoplasia, one as bone infarction and one as normal cortical bone. Positive predictive value for this strategy was 66.7%. Results of this study suggest that nuclear medical bone imaging with targeted radiography is a quick, noninvasive technique with a good positive predictive value for evaluation of the skeleton for metastatic or multicentric sites of neoplasia.     

MAGNETIC RESONANCE IMAGING OF THE EQUINE DIGIT WITH CHRONIC LAMINITIS

Chronic laminitis is a severe disease affecting the equine digit. It was hypothesized that magnetic resonance (MR) imaging would improve visualization of structures within the foot and pathology associated with chronic laminitis. This study aimed to describe the MR imaging findings in chronic laminitis, compare different pulse sequences for visualization of pathology, and to compare MR imaging with standard radiography. Twenty (10 forelimb, 10 hindlimb) cadaver limbs from 10 horses clinically diagnosed with chronic laminitis (group L) and 10 limbs without laminitis (group N) were used. Lateromedial radiographs and sagittal and transverse MR images of the foot were obtained. Radiographs and MR images were evaluated for anatomic definition and evidence of pathology. Dorsal hoof wall thickness and angle of rotation and displacement distance of the distal phalanx were measured. Comparisons were made between group L and N, forelimb and hindlimb within each horse, and MR imaging and radiography. Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically.     

Contrast radiography in the equine orthopaedic case

Routine contrast radiography has a valuable role in equine orthopaedics, providing additional information to standard radiography. However, ultrasonography provides additional information with respect to soft tissue pathology not appreciable when using contrast radiography alone, particularly in the investigation of synovial sepsis, ligament and tendon pathology, and osteochondral defects. The benefits of contrast media in more advanced imaging modalities such as computed tomography are just being recognised clinically.     

EVALUATION OF SURVEY RADIOGRAPHY, LINEAR TOMOGRAPHY AND COMPUTED TOMOGRAPHY FOR DETECTING EXPERIMENTAL LESIONS OF THE CRIBRIFORM PLATE IN DOGS

Survey radiography, linear tomography, and computed tomography were used to image cribriform plate lesions that were created experimentally using intramedullary pins in 18 dog cadaver skulls. Computed and linear tomographic images were taken along the dorsal imaging plane. Studies were independently reviewed by five observers. Results were combined so that the relative sensitivity, specificity, and accuracy of each imaging technique could be compared using chi-square analysis. Computed tomography proved to be significantly more sensitive and accurate (p<0.05) than either linear tomography or survey radiography. Computed tomographic images were consistently of good to excellent quality for imaging the cribriform plate. It was concluded that computed tomography of the skull using a dorsal imaging plane was the best available imaging modality for detecting 3-mm and 5-mm experimentally created cribriform plate defects.     

Nuclear Medical Bone Imaging and Targeted Radiography for Evaluation of Skeletal Neoplasms in 23 Dogs

Nuclear medical bone imaging was used in combination with targeted radiography to detect metastatic or multicentric lesions in 23 dogs with skeletal neoplasms. Each dog with a radio-graphically diagnosed skeletal neoplasm was injected with Technetium-99m labeled methylene diphosphonate (^99mTc-MDP) (15.0 mCi intravenously) for whole body imaging. All areas with increased uptake of ^99mTc-MDP were radiographed. In 19 dogs, the amount of bone shaft involvement in primary sites indicated by bone imaging was larger than the amount indicated by radiography. Eighteen dogs had secondary areas of increased ^99mTc-MDP uptake, six of which had secondary areas that were suspected radiographically to be neoplastic. Four dogs had lesions characterized histologically as neoplasia, one as bone infarction and one as normal cortical bone. Positive predictive value for this strategy was 66.7%. Results of this study suggest that nuclear medical bone imaging with targeted radiography is a quick, noninvasive technique with a good positive predictive value for evaluation of the skeleton for metastatic or multicentric sites of neoplasia.