A magnetic-resonance-compatible limb-positioning device to facilitate magic angle experiments in vivo.

Owing to their highly ordered structure, tendons and cartilage appear with low signal intensity when imaged using magnetic resonance imaging (MRI) scanners. A significant increase in signal can be observed when these structures are oriented at 55 degrees (termed the magic angle) with respect to the static field B0. There is a clear clinical importance in exploiting this effect as part of the diagnosis of injury. Experimental studies of this phenomenon have been made harder by the practical difficulties associated with tissue positioning and orientation in the confined environment of closed-bore scanners. An MRI-compatible mechatronic system has been developed, which is capable of positioning a number of limbs to a desired orientation inside the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor consisting of a heavily geared-down air turbine, presenting high torques and good accuracy. The system is shown to be magnetic resonance compatible and the results of preliminary trials using the device to image the Achilles tendon of human volunteers at different orientations are presented. An increase of four fold to thirteen fold in signal intensity can be observed at the magic angle.

Comparison of magnetic resonance imaging and conventional triple assessment in locally recurrent breast cancer.

BACKGROUND: Magnetic resonance imaging (MRI) was compared with triple assessment (clinical examination, cytology and mammography) in the differentiation of post-treatment changes from local recurrence of breast carcinoma. METHODS: Thirty patients treated previously by breast conservation surgery and radiotherapy with clinical suspicion of local recurrence were evaluated prospectively by triple assessment and MRI. Breast MRI was performed on a 1-tesla scanner using a T1-weighted three-dimensional fast low angle shot pulse sequence before and after contrast enhancement. RESULTS: Local recurrence was confirmed histologically in 14 patients. Of these, mammography identified seven (sensitivity 50 per cent), cytology 11 (sensitivity 79 per cent) and breast MRI 13 (sensitivity 93 per cent). Compared with histological measurement, breast MRI allowed an accurate estimation of the extent of local recurrence (r2 = 0.98). Morphologically abnormal areas without contrast enhancement correlated with postradiation changes. False-positive contrast enhancement was seen in two patients (specificity 88 per cent) in whom histology confirmed inflammatory changes only. CONCLUSION: Breast MRI is useful in the evaluation of patients with a high clinical suspicion of local recurrence within the irradiated conserved breast.