Radiology, Vol 153, 425-433, Copyright © 1984 by Radiological Society of North America
A strategy for magnetic resonance imaging of the head: results of a semi-empirical model. Part II
RT Droege, SN Wiener and MS Rzeszotarski
A semi-empirical model was used to identify specific pulse sequences that
cause most lesions to appear distinctly brighter than normal tissues in
magnetic resonance (MR) images of the head. Clinical trials confirm the
utility of these sequences for patient screening. As a result, a strategy
for effective and efficient MR imaging of the head is proposed. The
previously described gray-scale model has been modified to account for the
effect of image noise. By means of computer simulation, 13,800 different
hypothetical cerebral lesions were imaged with a variety of pulse
sequences. A number of conclusions resulted. First, two sequences are
expected to be sufficient to visualize most intracranial lesions, a
"diagonal" SE sequence (e.g., SE 2500/80) and an IR sequence with a short
inversion time (e.g., IR 1800/200). These sequences are orthogonal, i.e.,
lesions missed by one are likely to be detected by the other. Second,
signal averaging the screening sequences is expected to be more effective
than optimized sequences when lesion tissue parameters differ little from
brain. Finally, the effectiveness of unaveraged screening sequences
suggests that improved signal-to- noise ratio (SNR) is not necessary for
the detection of most large lesions. Therefore, the increased SNR
achievable through signal averaging or increased field strength might best
be utilized to improve spatial resolution so that smaller lesions can be
detected.
