Assessment of Human Disc Degeneration and Proteoglycan Content Using T1ρ-weighted Magnetic Resonance Imaging

Autor: Andrew J. Wheaton, Wade Johannessen, Alykhan Kurji, Arijitt Borthakur, Ravinder Reddy, Dawn M. Elliott, Joshua D. Auerbach
Rok vydání: 2006
Předmět:
Zdroj: Spine. 31:1253-1257
ISSN: 0362-2436
DOI: 10.1097/01.brs.0000217708.54880.51
Popis: Degenerative disc disease afflicts nearly 12 million people in the United States. Although a single initiating cause of degeneration has not been identified, early degenerative changes occur in the nucleus pulposus.1,2 Breakdown of the large aggregating proteoglycans reduces the capacity of the nucleus pulposus to attract and bind water, leading to a loss of disc hydration and decreased hydrostatic pressure.3,4 Ultimately, degeneration progresses to decreased disc height, structural changes in the lamellar architecture of the anulus fibrosus, anular tears and rim lesions, and the formation of osteophytes.5-7 The success of treatment strategies aimed at halting the progression of disc degeneration will require detection of the early stages of the disease, particularly changes in the extracellular matrix content of the nucleus pulposus. Conventional magnetic resonance imaging (MRI) techniques provide excellent detection of late-stage degenerative changes (i.e., changes in disc morphology, height, hydration, bulge, and herniation).8,9 However, these methods are not sensitive to early degenerative changes in the matrix content of the disc.10 Delayed gadolinium-enhanced MRI has been used to quantify proteoglycan in articular cartilage.11,12 However, the contrast agent must be administered intravenously, and diffusion into the cartilage requires a long time.13 This is a significant limitation in the avascular intervertebral disc, in which the negative fixed charged density of the nucleus pulposus hinders diffusion of ionic contrast agents.14,15 Sodium MRI has also been used to measure proteoglycan in articular cartilage.16-18 However, its clinical use is somewhat limited by a low spatial resolution and the need for instrumentation modifications for use on a clinical scanner. Spin-lock MRI techniques have been used to provide noninvasive measures of degeneration in articular cartilage and may potentially be used to assess degeneration in the intervertebral disc. Spin-lock pulses are low power rf pulses applied directly on-resonance with the Larmor precession frequency, locking the magnetization vector into a rotated frame. The relaxation that occurs after the application of a spin-lock pulse is referred to as spin-lattice relaxation in the rotating frame, or T1ρ relaxation. Spin-lock allows the coupling of spins to frequencies that are generally lower than the Larmor frequency. Therefore, slow motion regimes can be studied, such as low frequency physicochemical interactions between water and extracellular matrix molecules. Thus, matrix changes, such as loss of proteoglycan, will be reflected in the T1ρ parameter. T1ρ-weighting provides T2-like images with the advantage of increased dynamic range to degenerative changes compared to conventional T2-weighting.19 In articular cartilage, T1ρ is strongly correlated with proteoglycan content and, thus, has been shown to detect early osteoarthritic changes.20-22 Recently, T1ρ-weighted images of bovine intervertebral disc tissue have been acquired.23 However, a relationship between T1ρ and intervertebral disc degeneration has not been established, nor has it been shown that T1ρ is sensitive to proteoglycan content in the disc. Thus, the objective of the present study was to demonstrate the use of T1ρ MRI for the assessment of degeneration and proteoglycan content in the human intervertebral disc. Quantitative T1ρ measurements were obtained from cadaveric human intervertebral disc tissue. Degenerative grade was assessed from standard T2-weighted images, and tissue was subsequently analyzed for total sulfated-glycosaminoglycan content, a measure of proteoglycan content.
Databáze: OpenAIRE
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