在進行膝關節的磁振造影時，偶爾會發現同一條韌帶竟然會產生訊號亮度上的差異，這引發了我們對差異發 生原因的好奇心。經文獻調查發現，這是因為其中一段韌帶恰好與主磁場呈特殊角度所致，此角度被稱為魔角。 為了對魔角與韌帶的關係有更詳盡的了解，邀請某位健康的同學，以磁振造影儀器進行人體膝關節的掃描，掃描 後圈選並量取膝關節韌帶中與主磁場呈不同角度的訊號，然後以儀器所附之軟體繪製角度與訊號強度的關係圖， 再以自行編寫的Matlab程式及Excel程式進行數據分析。研究結果指出，韌帶的訊號在某些角度較高，某些角 度較低，而且有特定的曲線分布。這是因為韌帶的主要成分是膠原，所以如果韌帶恰好與主磁場成一定角度，則 這段韌帶在縱向驰緩及質子密度的加權影像中會因結構的關係而呈現較高的訊號。我們因此可做出下列結論：在 做正常膝關節掃描時，應注意魔角的存在，做適度的調整以避免誤診。

When performing magnetic resonance imaging of the knee joint, sometimes it is found that the same ligament had different signal brightness, which induced our curiosity about the cause of these differences. According to literature investigation, it is believed that part of the ligament has a particular angle with the main magnetic field. This angle is known as the “magic angle”. In order to deeper understand the relationship between magic angle and ligaments, a healthy classmate is invited to be the subject, and his knee joint was scanned by a Siemens magnetic resonance (MR) imaging instrument. After the MR images were acquired, the regions of interested (ROIs) were picked up and there signal intensities were measured. Then, the relationship between the angles and signal intensities were established with the built-in software. Finally, the data were analyzed by the Matlab program and Excel program. The results indicated that the ligament signals are higher at certain angles, and had a specific distribution curve. This is because the main component of the ligament is collagen. If the ligament is at a particular angle to the main magnetic field, the ligament will show a higher signal intensity in T1 weighted image (T1WI) and proton density weighted image (PDWI). In conclusion, we should pay attention on the existence of magic angle when applying the normal MRI knee scan and suitable adjustments may need to avoid misdiagnoses.