Amy S. Tidwell

Advanced imaging concepts: A pictorial glossary of CT and MRI technology

This article serves as an illustrative glossary of concepts related to computed tomography (CT) and magnetic resonance imaging (MRI) technology. The principles of tomography, digital processing, image resolution, CT windowing, CT gray levels, contrast enhancement, and MRI spin echo pulse sequences are reviewed. Techniques not commonly described for use in animal patients are also introduced, and include gradient echo, short time of inversion recovery, fluid attenuated inversion recovery and fat saturation pulse sequences, fast imaging, MRI angiography, perfusion and diffusion imaging, brain activation, CT angiography/functional CT, interventional procedures, and three-dimensional CT.

Alternative imaging of the lung

This article illustrates the roles of ultrasonography, scintigraphy, and computed tomography (CT) as alternative techniques for pulmonary imaging in small animals. The advantages and limitations of each modality, normal anatomic features, and technical considerations will be discussed. Selected applications will be examined and include pulmonary consolidation, neoplasia and other masses, atelectasis, pneumothorax, dystrophic mineralization, diffuse infiltrative disease, and pulmonary embolism. The use of ultrasound and CT-guided interventional procedures will also be briefly discussed.

Ultrasonography of the Thorax (Excluding the Heart)

Until recently, ultrasonography has had a subordinate role in the evaluation of the thorax in both small animals and humans, most likely due to the inability of sound to penetrate air-filled lung. When pathologic processes such as pleural effusion and lung consolidation provide an acoustic window to the thorax, however, thoracic ultrasonography becomes feasible. As this article illustrates, ultrasonography may be effectively employed in the diagnosis and management of various thoracic wall, pleural, mediastinal, pulmonary, and diaphragmatic diseases by providing valuable information not obtainable with routine radiography and enabling percutaneous aspiration or tissue core biopsy of lesions.

MAGNETIC RESONANCE IMAGING OF NORMAL AND ABNORMAL BRAIN PERFUSION

The brain is highly susceptible to injury from any process that deprives its cells of oxygen, glucose, and other essential nutrients, and is therefore critically dependent on blood flow or perfusion. With hypoperfusion or ischemia, blood flow to the brain may be diminished to a level incompatible with normal function, eventually leading to acute ischemic stroke. Magnetic resonance (MR) imaging is one of several imaging methods used to evaluate brain perfusion and stroke. Using a multisequence approach comprised of conventional spin echo, inversion recovery, and heme-sensitive gradient echo pulse sequences, MR angiography, and diffusion and perfusion sensitive techniques, MR imaging is capable of identifying vascular lesions, measuring abnormal blood flow, and depicting the metabolic and structural consequences of ischemia. MR imaging objectives and strategies for the diagnosis of acute ischemic stroke in humans and animals, terminology, pathophysiology, and normal vascular anatomy are reviewed.

Primary mycoplasma pneumonia associated with reversible respiratory failure in a cat

A young adult cat was evaluated for respiratory failure. Diagnostic testing, including computed tomography and culture, documented a primary Mycoplasma species pneumonia. The cat was treated aggressively with supportive care, including mechanical ventilation and appropriate antibiotics including doxycycline, and made a complete recovery. This is a unique case in respect of the severity of the Mycoplasma species pneumonia as well as the cats recovery from severe lung injury.

VALUE OF FAT SUPPRESSION IN GADOLINIUM‐ENHANCED MAGNETIC RESONANCE NEUROIMAGING

T1-weighted, gadolinium-enhanced magnetic resonance imaging is frequently used to investigate neurologic disease in small animals; however, the abundance of hyperintense adipose tissue adjacent to neural structures, particularly the cranial nerves and spinal cord, can decrease the conspicuity of contrast-enhanced tissues on T1-weighted images. For this reason, chemical fat saturation techniques are used to suppress the signal of adipose tissues, enabling improved depiction of gadolinium-enhanced structures and detection of lesions affecting the nervous system.

GM1-gangliosidosis in American black bears: Clinical, pathological, biochemical and molecular genetic characterization

G(M1)-gangliosidosis is a rare progressive neurodegenerative disorder due to an autosomal recessively inherited deficiency of lysosomal β-galactosidase. We have identified seven American black bears (Ursus americanus) found in the Northeast United States suffering from G(M1)-gangliosidosis. This report describes the clinical features, brain MRI, and morphologic, biochemical and molecular genetic findings in the affected bears. Brain lipids were compared with those in the brain of a G(M1)-mouse. The bears presented at ages 10-14 months in poor clinical condition, lethargic, tremulous and ataxic. They continued to decline and were humanely euthanized. The T(2)-weighted MR images of the brain of one bear disclosed white matter hyperintensity. Morphological studies of the brain from five of the bears revealed enlarged neurons with foamy cytoplasm containing granules. Axonal spheroids were present in white matter. Electron microscopic examination revealed lamellated membrane structures within neurons. Cytoplasmic vacuoles were found in the liver, kidneys and chondrocytes and foamy macrophages within the lungs. Acid β-galactosidase activity in cultured skin fibroblasts was only 1-2% of control values. In the brain, ganglioside-bound sialic acid was increased more than 2-fold with G(M1)-ganglioside predominating. G(A1) content was also increased whereas cerebrosides and sulfatides were markedly decreased. The distribution of gangliosides was similar to that in the G(M1)-mouse brain, but the loss of myelin lipids was greater in the brain of the affected bear than in the brain of the G(M1) mouse. Isolated full-length cDNA of the black bear GLB1 gene revealed 86% homology to its human counterpart in nucleotide sequence and 82% in amino acid sequence. GLB1 cDNA from liver tissue of an affected bear contained a homozygous recessive T(1042) to C transition inducing a Tyr348 to His mutation (Y348H) within a highly conserved region of the GLB1 gene. The coincidence of several black bears with G(M1)-gangliosidosis in the same geographic area suggests increased frequency of a founder mutation in this animal population.