Variable flip angle T1 mapping and multi-echo T2 and T2* mapping magnetic resonance imaging sequences allow quantitative assessment of canine lumbar disc degeneration

Nora Bouhsina, Léa Tur, Jean-Baptiste Hardel, Stéphane Madec, Dominique Rouleau, Floriane Etienne, Jérôme Guicheux, Johann Clouet, Marion Fusellier

Background: Intervertebral disc (IVD) degeneration is a common condition in dogs that can cause pain and neurological deficits. Magnetic resonance imaging (MRI) is the gold standard for diagnosing IVD degeneration, but conventional MRI sequences are limited in quantifying the severity or progression of IVD degeneration. Mapping MRI sequences, such as T1, T2, and T2* mapping, can measure the relaxation times of the nucleus pulposus (NP) and reflect the molecular changes of the IVD.

Study: The objective of this prospective, method comparison study was to evaluate variable flip angle T1 mapping and multiecho T2 and T2* mapping as methods for quantifying canine lumbar IVD degeneration in twenty canine patients without clinical signs of spinal disease. The MRI relaxation times of the NP were correlated with the radiographic IVD widths and the Pfirrmann grading based on standard T2-weighted sequences.

Methods: Ventro-dorsal and lateral radiographs of the lumbar spine and MRI images of the spine from T13 to S1 were obtained for each patient. The ventral and dorsal IVD widths were measured on radiographs, and the lumbar IVDs were assigned a qualitative Pfirrmann grade based on T2-weighted images. The T1, T2, and T2* relaxation times of the NP were measured on corresponding maps using manual-drawn regions of interest (ROI). The intra- and interrater reliability, the correlation, and the differences between the imaging parameters were assessed using statistical tests.

Results: The intra- and interrater agreement were strong for all the imaging parameters. The ventral and dorsal IVD widths and the T1, T2, and T2* relaxation times of the NP were negatively correlated with the Pfirrmann grading4. Significant differences in the relaxation times were found between different Pfirrmann grades, especially between grade I and the other grades.

Limitations: The study had a small sample size and a low representation of severely degenerated IVDs. The study did not include dogs with clinical signs of spinal disease, vertebral malformations, or spondylosis. The study did not compare the relaxation times with the molecular composition of the NP or the clinical pain scores of the dogs.

Conclusions: The study showed that T1, T2, and T2* MRI mapping sequences are feasible, repeatable, and reproducible in dogs. The relaxation times of the NP decreased when the Pfirrmann grades increased, indicating that these methods can quantify the IVD degeneration. These methods may be useful for evaluating the effects of regenerative treatments in future longitudinal studies.

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