Magnetic Resonance Imaging—a General Overview of Principles and Examples in Veterinary Neurodiagnosis

Abstract

Magnetic resonance imaging (MRI), a noninvasive technique that provides accurate, detailed, anatomic images, has had a major impact in the diagnosis of human disease. This technique is based upon the inherent magnetic properties of certain nuclei. Induction of the nuclei into a low energy state is achieved by placing them in a static magnetic field. The nuclei may then be excited into a high energy state by application of a radio frequency pulse. When the second field is stopped, the nuclei return to ground state and emit the absorbed energy in the form of a radio signal. This signal is received by a coil that generally surrounds the specimen and converted to an anatomic image through a process of computerassisted reconstruction. Contrast is altered by applying the second pulse in different sequences (saturation recovery, inversion recovery, and spin echo) and using enhancing agents such as gadolinium. In this paper, we present an overview of the general principles of MRI and some clinical examples in dogs and cats with central nervous system disease.

Imagem por ressonância magnética: princípios básicos

“…Ela ocorre por meio da relaxação spin-lattice e da relaxação spin-spin, as quais são definidas por duas constantes exponenciais de tempo T1 e T2 respectivamente (THOMSON et al, 1993). Imediatamente após a aplicação do pulso de RF, o vetor (Mo) é nutado em direção ao plano xy, criando Mxy.…”

“…Se o tempo de repetição (TR) for mais curto do que o T1 do tecido, o núcleo não retornará ao equilíbrio antes do próximo pulso de RF, e o tecido é dito como estando saturado (sem sinal). Dessa forma, a intensidade do sinal aumenta à medida que o tempo de relaxação do tecido diminui (THOMSON et al, 1993) …”

“…Dessa forma, a coerência de fase é perdida. A constante de tempo para essa forma de relaxação, chamada de T2, é o período de tempo durante o qual 63,2% do sinal é perdido (THOMSON et al, 1993) (Figura 4A). Os valores de T2 da maioria dos tecidos biológicos estão entre 50 e 100msec, enquanto o valor do líquor é de 250msec.…”

Studies on head and collum of the horse by means of Magnetic Resonance Imaging with case reports

“…In der Veterinärmedizin findet die Magnetresonanztomographie insbesondere bei der Untersuchung der Wirbelsäule, des Zentralen Nervensystems sowie des Muskuloskelettalen Systems Anwendung (Crass et al 1992, Martinelli et al 1997, Sanders et al 2001, Thomson et al 1993, Tucker et al 1999 : kennzeichnet den Proc. coronoideus des Ramus mandibulae; hier wird die Problematik der Knochendarstellung deutlich (hypointens: Kortikalis, hyperintens: Spongiosa).…”

Visualization of the Topographical Structure of the Anesthetized Mouse Brain by MR Microimaging.

“…In brief, Magnetic resonance imaging (MRI) is now widely employed as a useful technique for clinical diagnosis in veterinary medicine much as in human medicine [1,3,11,12]. This non-invasive technique is quite useful for medium-sized animals, but it is hard to visualize the detailed structures in tissues and organs of small laboratory animals such as rats and mice since they must be imaged by small voxels with weak MR signals and low signal/noise (S/N) ratios [5,12].…”