Normal feline brain: clinical anatomy using magnetic resonance imaging

The purpose of this study was to provide a clinical anatomy atlas of the feline brain using magnetic resonance imaging (MRI). Brains of twelve normal cats were imaged using a 1.5 T magnetic resonance unit and an inversion/recovery sequence (T1). Fourteen relevant MRI sections were chosen in transverse, dorsal, median and sagittal planes. Anatomic structures were identified and labelled using anatomical texts and Nomina Anatomica Veterinaria, sectioned specimen heads, and previously published articles. The MRI sections were stained according to the major embryological and anatomical subdivisions of the brain. The relevant anatomical structures seen on MRI will assist clinicians to better understand MR images and to relate this neuro-anatomy to clinical signs.     

Clinical anatomy of the canine brain using magnetic resonance imaging.

The purpose of this study was to produce an magnetic resonsnce (MR) image atlas of clinically relevant brain anatomy and to relate this neuroanatomy to clinical signs. The brain of a large mixed breed dog was imaged in transverse, sagittal, and dorsal planes using a 1.5 T MR unit and the following pulse sequences: Turbo (fast) spin echo (TSE) T2, T1, and T2- weighted spatial and chemical shift-encoded excitation sequence. Relevant neuroanatomic structures were identified using anatomic texts, sectioned cadaver heads, and previously published atlases. Major subdivisions of the brain were mapped and the neurologic signs of lesions in these divisions were described. TSE T2-weighted images were found to be the most useful for identifying clinically relevant neuroanatomy. Relating clinical signs to morphology as seen on MR will assist veterinarians to better understand clinically relevant neuroanatomy in MR images.     

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.     

MAGNETIC RESONANCE IMAGING OF THE BRAIN AND COELOMIC CAVITY OF THE DOMESTIC PIGEON (Columba livia domestica)

The technical feasibility of performing magnetic resonance imaging (MRI) in domestic pigeons was investigated. Imaging was performed with a 1.5 Tesla magnet using a human knee surface coil. The head and coelomic cavity of isoflurane-anesthetized birds were imaged in the dorsal, sagittal, and transverse planes to produce T1-weighted, T2-weighted, and contrast-enhanced T1-weighted images. The birds were then euthanatized, formalin perfused, frozen, and sectioned in the corresponding anatomic planes. The anatomy defined by MRI was correlated with gross anatomic sections made from the same birds. The following CNS structures were identified: cerebral hemispheres, cerebellum, optic chiasm, optic lobes, brain stem, and cranial spinal cord. The cornea, lens, and vitreous were also well differentiated in dorsal section MRI's. The abdominal organs identified included proventriculus, ventriculus, intestines, cloaca, liver, kidneys, spleen, testes, and ovary. The hepatic and renal vasculature were well defined.     

MAGNETIC RESONANCE IMAGING OF THE NORMAL EQUINE BRAIN

The purpose of this investigation was to define the magnetic resonance (MR) imaging appearance of the brain and associated structures of the equine head. MR images were acquired in oblique dorsal (T2-weighted), sagittal (T1-weighted), and transverse planes (T2-weighted), using a magnet of 1.5 Tesla and a human body coil. Relevant anatomic structures were identified and labeled at each level. The resulting images provided excellent anatomic detail of the cranioencephalic structures. Annotated MR images from this study are intended as a reference for clinical imaging studies of the equine head, specially in the diagnosis of brain diseases in the horse.     

MAGNETIC RESONANCE IMAGING OF THE NORMAL EYE AND ORBIT OF A SCREECH OWL (OTUS ASIO)

Magnetic resonance images of a screech owl ( Otus asio ) were acquired to identify the normal anatomic components of the eye'and orbit. T1-weighted, proton-density, and T2-weighted images were obtained in the straight sagittal, oblique dorsal, and oblique sagittal planes. Signal intensity for the various orbital structures differed between the three resonance techniques. T1-weighted images provided the best anatomic detail of ocular and orbital structures. The oblique dorsal and oblique sagittal planes were superior for evaluating the optic nerve in its entirety.     

LOW-FIELD MAGNETIC RESONANCE IMAGING OF THE EQUINE TARSUS: NORMAL ANATOMY

The objective of this study was to define the normal gross anatomic appearance of the adult equine tarsus on a low-field magnetic resonance (MR) image. Six radiographically normal, adult, equine tarsal cadavers were utilized. Using a scanner with a 0.064 Tesla magnet, images were acquired in the sagittal, transverse and dorsal planes for T1-weighted and the sagittal plane for T2-weighted imaging sequences. Anatomic structures on the MR images were identified and compared with cryosections of the imaged limbs. Optimal image planes were identified for the evaluation of articular cartilage, subchondral bone, flexor and extensor tendons, tarsal ligaments, and synovial structures. MR images provide a thorough evaluation of the anatomic relationships of the structures of the equine tarsus.     

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.     

Sectional anatomic and magnetic resonance imaging features of coelomic structures of loggerhead sea turtles

OBJECTIVE: To compare cross-sectional anatomic specimens with images obtained via magnetic resonance imaging (MRI) of the coelomic structures of loggerhead sea turtles (Caretta caretta). ANIMALS: 5 clinically normal live turtles and 5 dead turtles. PROCEDURES: MRI was used to produce T1- and T2- weighted images of the turtles, which were compared with gross anatomic sections of 3 of the 5 dead turtles. The other 2 dead turtles received injection with latex and were dissected to provide additional cardiovascular anatomic data. RESULTS: The general view on the 3 oriented planes provided good understanding of cross-sectional anatomic features. Likewise, major anatomic structures such as the esophagus, stomach, lungs, intestine (duodenum and colon), liver, gallbladder, spleen, kidneys, urinary bladder, heart, bronchi, and vessels could be clearly imaged. It was not possible to recognize the ureters or reproductive tract. CONCLUSIONS AND CLINICAL RELEVANCE: By providing reference information for clinical use, MRI may be valuable for detailed assessment of the internal anatomic structures of loggerhead sea turtles. Drawbacks exist in association with anesthesia and the cost and availability of MRI, but the technique does provide excellent images of most internal organs. Information concerning structures such as the pancreas, ureters, intestinal segments (jejunum and ileum), and the reproductive tract is limited because of inconsistent visualization.     

Anatomy of the cranioencephalic structures of the camel (Camelus dromedarius L.) by imaging techniques: a magnetic resonance imaging study

The objective of this study was to define the anatomy of the cranioencephalic structures and associated formations in camel using magnetic resonance imaging (MRI). MR images were acquired in sagittal, transverse and oblique dorsal planes, using spin-echo techniques, a magnet of 1.5 T and a standard human body coil. MR images were compared with corresponding frozen cross-sections of the head. Different anatomic structures were identified and labelled at each level. The resulting images provided excellent soft tissue contrast and anatomic detail of the brain and associated structures of the camel head. Annotated MR images from this study are intended to be a reference for clinical imaging studies of the head of the dromedary camel.     

EVALUATION OF MAGNETIC RESONANCE IMAGING TECHNIQUES IN THE EQUINE DIGIT

An anatomic study of the equine digit using magnetic resonance imaging (MRI) was performed. Seventeen isolated forelimbs and one hindleg of nine warmblood horses were imaged in transverse, sagittal, and dorsal planes with a 1.5 Tesla magnet using T1-, T2- proton density-weighted spin echo sequences as well as T2 gradient echo sequences. One scan plane in each horse was compared with corresponding anatomic and histologic sections. The best imaging planes to visualize various anatomic structures were determined. Fibrocartilage was visualized in the insertion of the deep digital flexor tendon and the suspensory ligament as well as in the distal sesamoidean ligaments. The correlation of MRI images with anatomic and histologic sections confirmed that all of the anatomic structures in the equine digit could be evaluated in PD and T2 studies.     

Magnetic Resonance Imaging of the Normal Canine Larynx

The purpose of this study was to define the normal anatomic structures in the canine larynx with magnetic resonance images. TI-weighted images were taken in the sagittal and transverse planes. The MR images were obtained comparing MR images to dissection planes. Magnetic resonance imaging provides excellent anatomic detail of laryngeal structures. Therefore, it is of value for diagnostic imaging of some respiratory diseases in the dog.     

MAGNETIC RESONANCE IMAGING OF NORMAL CANINE CARPAL LIGAMENTS

Magnetic resonance imaging was conducted on previously frozen left carpi from six normal dogs using a 1.5 Tesla magnet in combination with a transmit/receive wrist coil. Three-millimeter thick T1-weighted spin-echo images and 1-mm thick T2*-weighted gradient-recalled 3-D images were obtained in dorsal and sagittal planes. Carpi were embedded, sectioned, and stained. Anatomic structures on the histologic sections were correlated with the MR images. All of the carpal ligaments plus the radioulnar articular disc and the palmar fibrocartilage were identified on MR images. The accessorio-quartile ligament, which had not been well described previously in dogs, was also identified. It originated on the accessory carpal bone and inserted on the fourth carpal bone. The T2*-weighted gradient echo imaging technique provided better images than T1-weighted technique, largely because thinner slices were possible (1 mm vs. 3 mm), resulting in less volume averaging of thin ligaments with surrounding structures. Although MRI is currently the imaging modality of choice to identify ligamentous injury in humans, further studies are needed to determine if abnormalities can be detected in canine carpal ligaments using MRI.     

INTRACRANIAL MAGNETIC RESONANCE IMAGING ARTIFACTS AND PSEUDOLESIONS IN DOGS AND CATS

Normal anatomic variation, study design, external factors, and tissue characteristics can all influence the manifestation of structures on magnetic resonance images (MRI). For the purpose of this review, imaging artifacts are considered to be nonpathologic abnormalities resulting from study design, intrinsic tissue characteristics, or external factors, while MRI pseudolesions are due to normal anatomic variation. Awareness of imaging artifacts and pseudolesions, as well as normal anatomic structures, is important when determining pathologic vs. normal or clinically insignificant abnormalities. The purpose of this report is to examine the literature to compile a review of selected artifacts and pseudolesions that are commonly encountered when imaging the canine and feline brain.     

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.     

MAGNETIC RESONANCE IMAGING OF THE CANINE BRAIN AT 3 AND 7 T

Magnetic resonance (MR) imaging of the canine brain is commonly acquired at field strengths ranging from 0.2 to 1.5 T. Our purpose was to compare the MR image quality of the canine brain acquired at 3 vs. 7 T in dogs. Low‐resolution turbo spin echo (TSE) T2‐weighted images (T2W) were obtained in transverse, dorsal, and sagittal planes, and high‐resolution TSE T2W and turbo spin echo proton density‐weighted images were obtained in the transverse and dorsal planes, at both 3 and 7 T. Three experienced reviewers evaluated 32 predetermined brain structures independently and without knowledge of field strength for spatial resolution and contrast. Overall image quality and evidence of artifacts were also evaluated. Contrast of gray and white matter was assessed quantitatively by measuring signal intensity in regions of interest for transverse plane images for the three pulse sequences obtained. Overall, 19 of the 32 neuroanatomic structures had comparable spatial resolution and contrast at both field strengths. The overall image quality for low‐resolution T2W images was comparable at 3 and 7 T. High‐resolution T2W was characterized by superior image quality at 3 vs. 7 T. Magnetic susceptibility and chemical shift artifacts were slightly more noticeable at 7 T. MR imaging at 3 and at 7 T provides high spatial resolution and contrast images of the canine brain. The use of 3 and 7 T MR imaging may assist in the elucidation of the pathogenesis of brain disorders, such as epilepsy.     

High field magnetic resonance imaging anatomy of feline carpal ligaments is comparable to plastinated specimen anatomy

Feline carpal ligament injuries are often diagnosed indirectly using palpation and stress radiography to detect whether there is instability and widening of joint spaces. There are currently no reports describing normal feline carpal ligament anatomy and the magnetic resonance imaging (MRI) appearance of the carpal ligaments. The objective of this prospective, anatomic study was to describe normal feline carpal ligament anatomy using gross plastinated specimens and MRI. We hypothesized that MRI could be used to identify the carpal ligaments as previously described in the dog, and to identify species specific variations in the cat. The study was conducted using feline cadaver antebrachii that were radiographed prior to study inclusion. Three limbs were selected for MRI to confirm repeatability of anatomy between cats. The proton density weighted pulse sequence was used and images were acquired in transverse, dorsal, and sagittal planes. Following MRI, the limbs were plastinated and a collagen stain was used to aid in identification of carpal ligament anatomy. These limbs were sliced in sagittal section, and a further six paired limbs were included in the study and sliced in transverse and dorsal planes. Anatomic structures were initially described using MRI and then subjectively compared with gross plastinated specimens. Readers considered the transverse MRI plane to be most useful for visualizing the majority of the carpal ligaments. Findings indicated that MRI anatomy of the carpal ligaments was comparable to plastinated anatomy; therefore MRI appears to be a beneficial imaging modality for exploration of feline carpal pathology.