Diffusion-weighted MRI of soft tissue tumours

The purpose of this study was to evaluate the clinical utility of a multi-shot spin-echo echo-planar (SE-EPI) diffusion-weighted sequence in the diagnostic work-up of soft tissue tumours. There were 29 patients, 16 with a benign lesion and 13 with a sarcoma. Four of the sarcomas were examined both before and after radiation therapy. Diffusion-weighted imaging was performed with a multi-shot SE-EPI sequence. The b values were 0 and 600 s/mm². Phase navigation and pulse trigging were applied. The apparent diffusion constant (ADC) value of a large region of interest (ROI) representing the lesion was measured and compared to diagnosis and treatment. The ADC values of the benign lesions (mean 1.8×10⁻³ mm²/s) overlapped with non-treated sarcomas (mean 1.7×10⁻³ mm²/s). The ADC value increased in all radiated sarcomas. A multi-shot SE-EPI diffusion imaging sequence of less than 2-min duration is technically feasible in soft tissue tumours of the extremities and the trunk. The ADC values of benign soft tissue tumours and sarcomas overlapped and could not be used to differentiate between the bulk of benign and malignant tumours. However, the increase in ADC values of soft tissue sarcomas after radiotherapy warrants further studies of diffusion imaging for evaluating therapy response.