DWI scan protocol considerations

A DWI scan is an EPI based acquisition and therefore suffers from image distortion. A good compromise between the level of distortion and the level of noise is critical to warrant good parametric data and accurate ADC values.

Consider these tradeoffs as you change scan parameters for images that are post processed with the READY View ADC protocol.

• Just as with all functional imaging, keep the level of noise as low as possible; reduce matrix size or increase image FOV or slice thickness if necessary.
• As the receive bandwidth increases, SNR decreases, chemical shift artifact decreases, minimum TE decreases (which means that the echo space decreases). As echo space decreases, geometric distortion decreases.
• Dual Spin Echo adds an additional refocusing pulse, which reduces eddy currents, decreases distortion, increases minimum TE, and decreases SNR. For abdominal scans, typically de-select the Dual Spin Echo option, which produces the shortest TE that is needed for bowel gas considerations and also increases SNR.
• When available, select Optimize TE on to reduce geometric distortion. With Optimize TE selected On, maximum gradient amplitudes are employed with the minimum possible TE (based on the b-value), and higher b-values are available.
• To create ADC maps, more than one b-value has to be specified.