Magnetic resonance imaging of bone marrow in the pelvis and femur of young dogs

The purpose of this study was to determine the magnetic resonance (MR) imaging characteristics of bone marrow in the pelvis and femur of normal, young dogs. Six greyhounds were imaged at 4, 8, 12, and 16 months of age. Sagittal images of the femur and dorsal images of the pelvis were obtained with T1-weighted, fast spin echo (FSE) T2-weighted, and short tau (T1) inversion recovery (STIR) sequences. On T1-weighted images areas with high signal intensity, similar to fat, included the femoral heads, mid-diaphysis of the femur, femoral condyles, and the body of the ilium. T2-weighted images were characterized by uniform intermediate signal intensity (less than fat, but greater than muscle) in the femoral head, high signal intensity, similar to fat, in the mid-diaphysis of the femur and ilial body, and intermediate to high signal intensity in the femoral condyle. By 16 months high signal intensity was seen in the diaphysis and distal metaphysis on both T1- and T2-weighted images. On STIR images the femoral head had intermediate to low signal intensity, compared with muscle. The mid-diaphysis of the femur was of low signal intensity, similar to fat, and the body of the ilium had mixed signal intensity at all ages. The femoral condyle had inhomogenous, intermediate to low signal intensity at 4 months, but was of uniform low signal intensity at 8-16 months.     

MAGNETIC RESONANCE IMAGING FEATURES OF BRAIN STEM ABSCESSATION IN TWO CATS

Premortem magnetic resonance imaging (MRI) was performed in two cats with brain stem abscessation confirmed post mortem by histology and recovery of multiple bacterial species. The MRI features of the abscesses were distinctive and included a thick and marked enhancement of the abscess capsule and extension of the lesion from a tympanic bulla in one cat. A focal area of increased signal intensity was present on T2-weighted images. A circumscribed area of decreased signal intensity was surrounded by a ring of increased signal intensity on precontrast T1-weighted images. A center of decreased signal intensity with a thick, markedly enhanced abscess capsule was observed on post contrast T1-weighted images. These findings are compared to the current experimental and clinical literature of brain abscess. The underlying pathogenesis of MRI features is reviewed.     

Magnetic Resonance Imaging and Cross Section Images of the Cat Thorax

Accurate interpretation of thoracic magnetic resonance images requires a thorough knowledge of anatomy of this region. The purpose of this communication is to describe the normal cross sectional anatomy of the thoracic cavity of the cat, using MR images, dissections and macroscopic sections. In this study, three cats were used. The animals were anesthetized and positioned in sternal recumbency in the MR scanner. MR imaging was performed at the Special Diagnostic Service of San Roque Clinic of Las Palmas de Gran Canaria with a superconducting magnet operating at a field strength of 1.5 Tesla and a human body coil. Spin echo pulse sequences were used to obtain T1-weighted images in tranverse and sagittal planes. At the conclusion of imaging, the cats were euthanatized for medical reasons unrelated to disease of thorax. The cats were frozen and then sectioned using an electric band saw. The cuts were matched as closely as possible to the MR images for identifying the normal planimetric anatomy of the thoracic structures. MR T1-weighted spin echo images provided excellent anatomic appearance of the thorax structures. In MR images the grey scale is directly related to the signal intensity of the thoracic cavity structures. Thus, fat and nerves had higher signal intensity compared with the lower signal intensity of the respiratory system. Bone marrow and muscles had a intermediate signal intensity and appeared gray. The intensity signal of the articular fluid permits a good differentiation of the opposing cartilage surfaces on all MR images. The planimetric or sectional anatomy of the thoracic cavity in the cat allows a correct morphologic and topographic evaluation of the anatomic structures, being helpful tool for the identification of the MR images. The information presented should serve as an initial reference to evaluate MR images of the feline thorax and to assist interpretation of lesions of this region.     

MENSURATION OF THE PITUITARY GLAND FROM MAGNETIC RESONANCE IMAGES IN 17 CATS

The objective of this retrospective study was to estimate using magnetic resonance imaging the size range of the pituitary gland in cats who had no evidence of pituitary disease. The pituitary gland was measured from transverse and sagittal magnetic resonance postgadolinium T1-weighted images in 17 cats. The cats were 0.83 to 15 years of age and weighed between 2.9 and 6.5 kg. Linear pituitary measurements were performed on a dedicated workstation using electronic calipers. Mean (+/- standard deviation) pituitary gland length was 0.54 cm (+/- 0.06 cm) and mean width was 0.50 cm (+/- 0.08 cm). Mean pituitary gland height measured on sagittal images was 0.34 cm (+/- 0.05) and measured on transverse images was 0.32 cm (+/- 0.04 cm). Mean pituitary volume was 0.05 cm3 (+/- 0.01 cm3). There was no significant correlation between cat weight (kg) and pituitary volume or age and pituitary volume. The pituitary gland appearance varied on pre- and postcontrast T1-weighted images. On the precontrast images, the majority of pituitary glands had a mixed signal intensity. On postcontrast images, uniform pituitary gland enhancement was seen commonly.     

Magnetic resonance imaging of the palmar aspect of the equine podotrochlear apparatus: normal appearance

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of MR imaging studies of 16 cadaver limbs. The articular aspect of the distal sesamoid bone was not evaluated in this study. Equine digits were imaged with a human knee radiofrequency coil in a 1.5 T magnetic field, using spin echo (SE) T1-weighted, turbo spin echo proton density (TSE PD)-weighted with and without fat saturation (FS), and FS TSE T2-weighted sequences. The limbs were dissected after imaging to validate the absence of gross abnormalities of the flexor aspect of the distal sesamoid bone, of the deep digital flexor tendon, and the distal impar sesamoidean ligament. Seven deep digital flexor tendons were subjected to histologic examination to exclude any microscopic tendon pathology. The anatomic structures of the podotrochlear apparatus were easily identified on MR images. Compact bone of the flexor cortex of the distal sesamoid bone had low intensity signal on all sequences. In 11 digits an increased signal was seen within the thickness of the sagittal eminence of the flexor cortex in SE T1-weighted images and in TSE PD-weighted images without FS. Trabecular bone had a granular appearance and high signal in SE T1-weighted sequences and TSE images without FS. The deep digital flexor tendon had low signal on FS T2-weighted images, while on short echo time sequences (T1- and PD-weighted sequences), the tendon signal varied depending on the relative orientation between its fibers and the static magnetic field. Seven tendons had stippled appearance due to small intratendonous foci of slightly increased signal on transverse T1-weighted images. MR imaging provides a thorough evaluation of the anatomical structure of the podotrochlear apparatus: A good knowledge of the MR imaging appearance and anatomy and an awareness of potential pitfalls will improve diagnostic specificity for the detection of pathologic changes.     

LOW-FIELD MAGNETIC RESONANCE IMAGING OF BONE MARROW IN THE LUMBAR SPINE, PELVIS, AND FEMUR IN THE ADULT DOG

The purpose of this study was to describe the appearance of normal bone marrow in seven adult dogs using low-field (0.3 T) magnetic resonance (MR) imaging. The areas imaged included the lumbar spine, pelvis, and femur. T1-weighted, fast spin-echo T2-weighted, and short tau (T1) inversion recovery (STIR) sequences were obtained at all locations. Histopathology was performed on sections from the sixth lumbar vertebral body, the wing of the ilium, and the femur (head and neck, mid-diaphysis, and condyle) for evaluation of cellularity and fat content. The lumbar spine and pelvic marrow MR images were similar in all dogs. The lumbar vertebral bone marrow was uniform, intermediate signal intensity, and isointense to muscle on all sequences. There was variation between dogs in the bone marrow distribution with MR imaging of the femur. In the proximal and mid-diaphysis of the femur there was patchy high-signal intensity on T1- and T2-weighted images, and hypointense foci on the STIR images. The distal femoral metaphysis had a variable pattern ranging from intermediate-to-high signal on T1- and T2-weighted images and intermediate-to-low signal on STIR images. The femoral condyles were uniformly high signal on T1- and T2-weighted images and hypointense on STIR images. Histopathologically there was a normal variation in the bone marrow cellularity. The marrow was normocellular (25–75% cellularity) for all sites examined except the femoral condyles, which were hypocellular (<25% cellularity).     

The density of equine tissue at 37 degrees C.

The density of the following equine tissues was measured: white and grey brain matter, myocardium, lung parenchyma, liver, spleen, gastrointestinal tract and contents, renal medulla and cortex, muscle, fat, tendon and bone. Statistical analysis indicated that there were highly significant differences in the values for density between horses and between tissues within horses. Values for density of eight different muscles were obtained for 18 horses and these were shown to differ highly significantly between horses and between muscles within horses. The values for splenic density differed highly significantly between those for knackery killed horses and for the barbiturate killed post morten room horses.     

Magnetic resonance imaging of the femoral head of normal dogs and dogs with avascular necrosis.

The purpose of this study was to describe the appearance of the femoral head of normal, young, small breed dogs, and dogs with avascular necrosis using low-field (0.3 T) magnetic resonance (MR) imaging. Images of the femoral heads were obtained in the dorsal plane, and included T1-weighted spin-echo, T2-weighted fast spin-echo, fast spin echo-inversion recovery, and fluid attenuated inversion recovery pulse sequences. MR imaging features of the asymptomatic femoral heads and necks included uniform high signal intensity compared with muscle on T1- and T2-weighted images. There was either uniform enhancement or no enhancement on postcontrast T1-weighted images. The MR imaging findings of dogs affected with avascular necrosis differed from those of asymptomatic dogs. Typically, the affected dogs had inhomogeneous intermediate to low-signal intensity within the femoral head and neck compared with muscle on T1-weighted images, inhomogeneous enhancement of the femoral head and/or neck on postcontrast T1-weighted images, and inhomogeneous low- to high- signal intensity within the femoral head and neck on T2-weighted images.     

Fibrocartilaginous embolic myelopathy in five cats

Five cats had clinical signs, radiographic findings, and cerebrospinal fluid analyses consistent with fibrocartilaginous embolic myelopathy. All cats had an acute onset of nonpainful, asymmetrical spinal cord signs (paresis or paralysis of one or more limbs). Magnetic resonance imaging was performed in three cats. On T2-weighted images, an intramedullary lesion was revealed that was hyperintense to normal spinal cord gray matter. On T1-weighted images, the lesion was isointense. Three of the cats were euthanized, and postmortem examination confirmed myelomalacia with intralesional fibrocartilaginous emboli. Two cats survived and were clinically improved within 3 weeks.     

TRANSCUTANEOUS ULTRASONOGRAPHY OF THE ABDOMEN IN THE NORMAL COMMON MARMOSET (CALLITHRIX JACCHUS)

Ultrasonographic examinations were performed on 17 clinically healthy adult common marmosets to gain information about the normal abdominal echoanatomy. The marmosets were 1.5-9 years of age and weighed between 328 and 506g. Marked species-specific differences compared with the cat or dog were noted. Good images of the kidneys, bladder, spleen, adrenal glands, liver, and the gastrointestinal tract could be obtained. The pancreas, caecum, and abdominal lymph nodes were not seen. The spleen was the least echogenic organ, followed by the medium echogenic liver and the sometimes isoechoic, but mostly hyperechoic renal cortex. The kidneys had a poor corticomedullary distinction. The prominent right lobes of the liver extended caudally far beyond the costal arch. The gallbladder had a bi- to multi-lobed appearance with a wide, tortuous cystic duct. The pylorus was centrally positioned. The adrenal glands were readily seen, but should not be confused with the adjacent spleen. A statistically significant (P<0.05) difference between female and male kidney, and right adrenal gland length was present.     

EVALUATION OF THE FELINE PANCREAS USING COMPUTED TOMOGRAPHY AND RADIOLABELED LEUKOCYTES

This study was designed to test the feasibility and utility of computed tomography and radiolabeled granulocytes in evaluating the feline pancreas in six normal cats. Autologous granulocytes were labeled with 99mTc-hexamethylpropyleneamine oxime (HMPAO) and injected into each cat. Whole body scintigraphic images were acquired at 1, 5, 15, and 30 minutes, and 1, 2, and 4 hours following injection. The following day, each cat was anesthetized and computed tomographic images of the abdomen were acquired both pre- and post-contrast. Following CT, a surgical pancreatic biopsy was collected. Feline granulocytes were successfully labeled with 99mTc-HMPAO with a labeling efficiency of 15-42% (average of 27%). An average of 5.42 x 10(7) cells in a 2 mL volume were injected into each cat. Less than 1 minute was required to acquire 500,000 count images. Granulocytes distributed predominantly to the lung, spleen and liver in order of decreasing activity. Only background activity was identified in the region of the pancreas. The pancreas was easily identified on CT images of the abdomen. The pancreas was hypoattenuating relative to both the spleen and liver. The pancreas enhanced with the administration of contrast medium, peaking immediately, then gradually clearing over the 30-minute test period. Following contrast medium administration the pancreas remained hypoattenuating relative to the spleen. All biopsies confirmed the absence of pancreatic inflammation in the study cats and no adverse effects were recognized as a result of pancreatic biopsy. Both computed tomography and radiolabeled granulocytes appear to hold promise as imaging procedures for the detection of feline pancreatitis. We predict that these described normal parameters may be altered in the face of inflammation, facilitating detection of feline pancreatitis. Data from cases of suspect feline pancreatitis are needed to evaluate these methods for clinical utility.     

LOW-FIELD MAGNETIC RESONANCE IMAGING OF THE CANINE STIFLE JOINT: NORMAL ANATOMY

Low-field magnetic resonance imaging (MRI) was performed on the stifle joints of four normal adult mongrel dogs using a 0.064 Tesla scanner. Markers were placed on each stifle joint to serve as reference points for comparing gross sections with the images. A T1-weighted sequence was used to image one stifle joint on each dog in the sagittal plane and the other stifle joint in the dorsal plane. The dogs were euthanized immediately following MRI and the stifle joints frozen intact. Each stifle joint was then embedded in paraffin, again frozen, and sectioned using the markers as reference points. On T1-weighted images, synovial fluid had low signal intensity (dark) compared to the infrapatellar fat pad which had a high signal intensity (bright). Articular cartilage was visualized as an intermediate bright signal and was separated from trabecular bone by a dark line representing subchondral bone. Menisci, fibrous joint capsule, and ligamentous structures appeared dark. In the true sagittal plane, the entire caudal cruciate ligament was often seen within one image slice. The patella was visualized as an intermediate bright signal (trabecular bone) surrounded by a low intensity signal (cortical bone). The trochlea and the intercondylar notch were difficult areas to analyze due to signal volume averaging of the curved surface of these areas and the presence of several types of tissues.     

MAGNETIC RESONANCE IMAGING OF THE NORMAL EYE AND ORBIT OF THE DOG AND CAT

Magnetic resonance (MR) images of the normal eye and orbit of the dog and cat were acquired. T1-weighted, proton-density, and T2-weighed images were obtained in the oblique dorsal, straight sagittal, and oblique sagittal planes. Signal intensity for the various orbital structures differed among the three resonance techniques. T1-weighted images provided the greatest contrast of the retrobulbar structures. T-1 weighted images also had the highest signal to noise ratio, thereby providing the best anatomic detail. Anatomic components of the globe, retrobulbar structures and ocular adnexa were easily seen in all MR sections. The oblique dorsal and oblique sagittal planes were superior for evaluating the optic nerve in its entirety.     

Pseudolayering artefact on postcontrast magnetic resonance images of the bladder of 18 dogs and three cats

An artefact was observed on postcontrast magnetic resonance imaging (mri) of the urinary bladder of several small animals; it took the form of a dark layer in the dependent (dorsal) part of the bladder, with a thin hyperintense layer on top of it, and a hypointense signal in the rest of the non-dependent (ventral) part. The mri database was searched for animals with T1-weighted images of the urinary bladder after the injection of gadolinium. Eighteen dogs and three cats were included in the study. The artefact was observed in 16 of the animals on the postcontrast images but not on the T1-weighted and T2-weighted precontrast images. A phantom experiment showed that the signal intensity observed on T1-weighted images decreased rapidly as the concentration of gadolinium increased from 6.25 mmol/l to 25 mmol/l. It is hypothesised that the early excretion of concentrated gadolinium into the bladder causes the pseudolayering artefact observed, which has also been reported in human patients.     

COMPARISON OF FLUID-ATTENUATED INVERSION RECOVERY AND T2-WEIGHTED MAGNETIC RESONANCE IMAGES IN DOGS AND CATS WITH SUSPECTED BRAIN DISEASE

To compare fluid-attenuated inversion recovery (FLAIR) and T2-weighted magnetic resonance (MR) imaging in small animal patients with suspected brain disease, paired sets of FLAIR and T2-weighted MR images of 116 dogs and cats were reviewed separately without any patient information. Images were rated as normal or abnormal using a five-point scale, and the distribution, signal intensity, and anatomic location of abnormalities were recorded. In 60 animals, both FLAIR and T2-weighted images were normal. In 50 animals, the same abnormalities were identified in both FLAIR and T2-weighted images. Overall, very good agreement was found between FLAIR and T2-weighted MR images (kappa = 0.88). FLAIR images had abnormalities that were not recognized in the corresponding T2-weighted images in six of 116 examinations (5%). In four of these, the abnormalities in FLAIR images were thought to represent pathology, including granulomatous meningoencephalitis in one dog, postictal edema in one dog, and undiagnosed lesions in two dogs. In the remaining two examinations, the abnormalities in FLAIR images were probably artifacts. No examples were found of intracranial abnormalities in T2-weighted images that were not visible in FLAIR images. In this study, acquiring FLAIR images in addition to T2-weighted images resulted in detection of otherwise occult abnormalities in relatively few patients.     

MAGNETIC RESONANCE IMAGING OF ACQUIRED TRIGEMINAL NERVE DISORDERS IN SIX DOGS

The medical records and magnetic resonance (MR) images of dogs with an acquired trigeminal nerve disorder were reviewed retrospectively. Trigeminal nerve dysfunction was present in six dogs with histologic confirmation of etiology. A histopathologic diagnosis of neuritis (n=2) or nerve sheath tumor (n=4) was made. Dogs with trigeminal neuritis had diffuse enlargement of the nerve without a mass lesion. These nerves were isointense to brain parenchyma on T1-weighted (T1W) precontrast images and proton-density-weighted (PDW) images and either isointense or hyperintense on T2-weighted (T2W) images. Dogs with a nerve sheath tumor had a solitary or lobulated mass with displacement of adjacent neuropil. Nerve sheath tumors were isointense to the brain parenchyma on T1W, T2W, and PDW images. All trigeminal nerve lesions enhanced following contrast medium administration. Atrophy of the temporalis and masseter muscles, with a characteristic increase in signal intensity on T1W images, were present in all dogs.     

THE EFFECTS OF A UNILATERAL ULTRASOUND-GUIDED RENAL BIOPSY ON RENAL FUNCTION IN HEALTHY SEDATED CATS

Complications of renal biopsies are well documented except for the change in renal function after a biopsy. Eighteen healthy, adult cats were divided into two groups (n = 9 cats/group). For the measurement of global and split renal function, Group 1 used the renal uptake of 99mTc-DTPA and Group 2 used the renal uptake of 99mTc-MAG3. Scintigraphic data were collected on days (-4), (-3), 0, 1, 2, and 4 post renal biopsy. Using ultrasound guidance, biopsies were taken from the right renal cortex on dO, before acquiring scintigraphic images. P - values less than 0.10 were considered significant due to the limited number of observations. The only statistically significant change (p = 0.08) in global renal function detected was by day following a unilateral renal biopsy. Cats imaged using 99mTc-MAG3 had discernible liver activity. A unilateral, ultrasound guided renal biopsy has minimal effect on renal function in normal, healthy sedated cats.     

SEQUENTIAL MAGNETIC RESONANCE IMAGING OF AN INTRACRANIAL HEMATOMA IN A DOG

An 8-year-old Yorkshire terrier developed acute onset coma and seizure after cranial trauma. Intracranial hemorrhage was suspected from the clinical signs and history. Low-field magnetic resonance (MR) imaging revealed a round mass within the right cerebral hemisphere, compressing the right lateral ventricle and displacing the longitudinal fissure to the left. The lesion was hypointense on T1-weighted images and hyperintense on T2-weighted images, consistent with an acute hemorrhage. MR imaging was performed every 24 h for 6 days from 1 h after the injury, and then on day 14 of hospitalization. With time, the signal intensity changed to hyperintense on Ti-weighted images. On T2-weighted images the center of the mass changed to hypointense, and then to hyperintense with a hypointense rim. These changes of signal intensity were related to hemoglobin oxidation.     

MAGNETIC RESONANCE IMAGING AND PATHOLOGIC FINDINGS ASSOCIATED WITH NECROTIZING ENCEPHALITIS IN TWO YORKSHIRE TERRIERS

Two young adult Yorkshire terriers had neurologic signs consistent with forebrain and brainstem involvement or forebrain involvement alone. On magnetic resonance imaging studies there were asymmetric bilateral lesions mainly in the cerebral cortex, and in the diencephalon. These areas were hyperintense on T2-weighted and FLAIR images, but hypointense or isointense on T1-weighted images. Lesions had a varying degree of contrast enhancement. Areas which were isointense on T1-weighted images had no contrast enhancement or only foci of contrast enhancement. Lesions with hypointensity in T1-weighted images had no enhancement or more frequently ring-like enhancement around the lesion. Necrotizing encephalitis was confirmed pathohistologically in both dogs. The degree of contrast enhancement appeared to be related to the degree of lymphohistiocytic inflammation on histologic examination.