Optimal pulse sequence for imaging hepatic metastases.

For magnetic resonance (MR) imaging studies in which the diagnosis is dependent on image contrast, it is essential that an optimized imaging technique be used. Using detection of hepatic metastases as an example, the authors describe a rational strategy for optimizing MR imaging technique. First, for a single patient with proved hepatic metastases, a variety of imaging sequences is discussed and evaluated, leading to characterization of the patient's hepatic tissues. Then the characteristics of the tissues of a representative patient population are presented. These are used to determine two optimal pulse sequences that maximize the achievable signal difference-to-noise ratio achievable in a fixed imaging time. The recommended imaging sequence for detection of hepatic metastases at 0.15 T is either a three-dimensional volume spin-echo (SE) sequence with echo time (TE) = 12 msec and repetition time (TR) = 184 msec or a multisection inversion recovery sequence with TE = 22 msec, inversion time = 250 msec, and TR = 1,375 msec. The variation of this optimum pulse sequence with field strength is also presented.