Timins M E, Erickson S J, Estkowski L D, Carrera G F, Komorowski R A
Department of Radiology, Medical College of Wisconsin, John L. Doyne Hospital, Milwaukee 53226, USA.
AJR Am J Roentgenol. 1995 Jul;165(1):109-14. doi: 10.2214/ajr.165.1.7785568.
Increased signal intensity within the distal portion of the supraspinatus tendon during MR imaging is a frequent observation even in healthy subjects. This finding has been variously attributed to the presence of fat, muscle, connective tissue, abnormal vascularity, or degenerative changes. More recently, the effect of tendon orientation in the static magnetic field (Bo) has been implicated. It has been shown that tendons at the magic angle of 55 degrees to Bo show markedly increased signal. This study was designed to determine the contribution of the magic-angle effect to the MR signal in the distal portion of the supraspinatus tendon.
Five healthy volunteers were imaged in a 1.5-T unit using short TR/TE sequences in standard supine position; they were then reimaged laterally flexed at the waist to reorient the plane of the distal portion of the supraspinatus tendon by approximately 20 degrees relative to Bo. In the second part of the study, three cadaveric shoulders were similarly imaged, first in standard position and then reoriented approximately 35 degrees by simple rotation of the specimen. The supraspinatus tendon was evaluated in each subject by noting the length of the segment with increased signal and the position of this segment relative to the insertion of the tendon on the greater tuberosity. Comparisons were made for each live and cadaveric subject between neutral and rotated positions.
Segments of increased signal changed in length and position for each live and cadaveric subject from the neutral to the reoriented position.
Our study suggests that tendon orientation contributes significantly to the presence of increased signal within the supraspinatus tendon, as caused by the magic-angle effect. Failure to recognize this effect may lead to diagnostic inaccuracy when evaluating the rotator cuff on short TR/TE sequences.
在磁共振成像（MR）中，即使在健康受试者中，也经常观察到冈上肌腱远端部分信号强度增加。这一发现被归因于脂肪、肌肉、结缔组织、异常血管或退行性改变的存在。最近，有人认为是肌腱在静磁场（Bo）中的取向产生了影响。研究表明，与Bo呈55度魔角的肌腱信号明显增强。本研究旨在确定魔角效应在冈上肌腱远端部分MR信号中的作用。
5名健康志愿者在1.5-T设备上采用短TR/TE序列进行标准仰卧位成像；然后让他们腰部侧屈再次成像，使冈上肌腱远端部分的平面相对于Bo重新定向约20度。在研究的第二部分，对3个尸体肩部进行类似成像，首先在标准位置成像，然后通过简单旋转标本使其重新定向约35度。通过记录信号增强节段的长度以及该节段相对于肌腱在大结节上附着点的位置，对每个受试者的冈上肌腱进行评估。对每个活体和尸体受试者在中立位和旋转位之间进行比较。
对于每个活体和尸体受试者，从中立位到重新定向位置，信号增强节段的长度和位置都发生了变化。
我们的研究表明，魔角效应导致的肌腱取向对冈上肌腱内信号增强的出现有显著影响。在使用短TR/TE序列评估肩袖时，若未认识到这种效应可能导致诊断不准确。
