Magnetization transfer contrast: MR imaging of the knee.

Abstract

The use of magnetization transfer contrast (MTC) in magnetic resonance imaging of the human knee was evaluated in this study. MTC is generated by irradiating the macromolecular protons in tissue with a low power off-resonance radio-frequency field. This results in a decrease in water proton signal intensity where a tight magnetic coupling between water and macromolecules exists. With this approach, the authors have demonstrated that MTC can improve contrast in standard single-section, gradient-recalled-echo images of the knee with regard to fat-muscle and cartilage-synovial fluid comparisons. The effect of changes in repetition time, echo time, and flip angle were also quantitatively evaluated. More important, MTC was shown to generate useful cartilage-synovial fluid contrast on high-resolution three-dimensional images, in which contrast is difficult to generate. This approach may not only provide better structural information about the knee, but may also provide noninvasive insight into the structure and biochemical composition of cartilage in vivo.

The morphology of articular cartilage assessed by magnetic resonance imaging (MRI)

“…Intraarticular contrast agents, which greatly enhance the delineation of the articular surface [6,10,21,22], are invasive and cause patient discomfort. Therefore other techniques have been developed to improve contrast, such as MTC (magnetic transfer contrast) [39,[42][43][44], MPRAGE (magnetization-prepared rapid gradient echo) [29], DESS (dual echo at steady state) [24] and fat suppression [30,37].…”

Ultrashort TE (UTE) Imaging of the Knee Cartilage at 3T

“…Clinical fat saturation techniques employ a non-selective saturation pulse to selectively suppress fat signals. There might be significant overlap between the spectrum of the short T2 species and that of the fat saturation pulse, resulting in significant suppression of the short T2 signals [6,13]. An optimized fat saturation pulse should have enough spectral bandwidth to cover the dispersed fat resonance frequencies at 3T, but minimal spectral overlap with that of the short T2 signals and therefore has typically a relatively long duration.…”

“…However, conventional fat saturation may be problematic in imaging tissues with very short T2s, which have a broad spectrum which may overlap with that of fat. As a result, fat saturation pulses may degrade the short T2 signals either directly, or as a result of magnetization transfer [6,13]. Various fat suppression pulses with different excitation profiles and frequency positions were investigated.…”

“…Articular cartilage can be divided into four zones, namely the superficial zone, the transitional or middle zone, the radial zone and the calcified zone, which have variable structural organization reflected by the variation in T2 ranging from ~20 to 40 ms for superficial layer to sub-millisecond for calcified cartilage [4][5][6][7][8][9]. Most of the currently available clinical and research MR imaging techniques, including proton-density weighted Fast Spin Echo (FSE) [10], T2-weighted FSE [11], gradient echo imaging [12], magnetization transfer [13], T2 mapping [14], delayed Gadolinium enhanced MR imaging (dGEMRIC) [15], and steady State Free Precession (SSFP) imaging [16][17][18] have focused on the superficial layers of cartilage. The study of early and late alterations to the deeper layers of cartilage, including the deepest radial zone and calcified cartilage, has been overlooked due to technical limitations (i.e., the minimal achievable TEs are too long to detect signal from the deeper layers of cartilage because of their very short T2s).…”

Evaluation of bioreactor-cultivated bone by magnetic resonance microscopy and FTIR microspectroscopy

“…In contrast, for a developing system the 31 P signal of bone is not very large owing to the exceedingly small amounts of mineral deposited, which can be overwhelmed by contributions from the phosphate ions present in the culture medium, phosphorylated cytosolic metabolites, and membrane phospholipids (22). MRM can also be used to evaluate the collagen content of tissues because collagen gives rise to a significant magnetization transfer (MT) effect (23,24). The MT effect is the result of crossrelaxation between mobile water protons and the less mobile hydroxyl groups on the collagen molecules (25,26).…”