Brain: Neoplasia—IntroductionVal M. Runge and Harold L. Sonnier38

For the evaluation of brain neoplasia, incommon with many other anatomic/patho-logic areas, one is confronted at 3 T withthe dilemma of whether to use the addi-tional available SNR for improved spatialresolution or to decrease scan time. Often,the scan that is adopted clinically repre-sents a compromise between the twoextremes. Figure 38–1 illustrates imagesfrom a patient with a brainstem (pontine)astrocytoma using T2-weighted FSE tech-nique. The spectrum of scan time andresultant image quality is illustrated, withthe acquisition time varying from 24 sec-onds to 59 seconds to 2:39 min:sec (A toC). Spatial (voxel) resolution varied from0.7 � 0.7 � 5 to 0.5 � 0.4 � 5 to 0.4 � 0.4 �2.5 mm3 (A to C). Patients with or suspect-ed of neoplastic disease in the brain repre-sent a subpopulation in which inadvertentmotion is often a problem in regard to scanquality. To ask such a patient to hold still—meaning moving well less than one half ofa mm—for a 5-min scan with an in-planeresolution of less than 0.5 � 0.5 mm2 and aslice thickness less than 5 mm is simplynot practical. A reasonable compromise isa 3- to 5-mm slice thickness, with an in-plane resolution of greater than 0.5 � 0.5mm2, which due to the robust nature ofFSE T2-weighted imaging at 3 T can beperformed in 1 to 2 min. Except for spe-cialty exams, such as the internal auditorycanal or pituitary, the additional spatialresolution possible with a 5-min T2-weighted scan at 3 T simply does not addimportant clinical information, as the dis-ease processes being examined are inthemselves typically large in dimensionrelative to pixel resolution.

As discussed in earlier chapters, an in-phase short TE (2.4 msec) 2D GRE scan isstrongly recommended for routine brainimaging at 3 T and is indeed critical forFigure 38–1

Chapter 38_p74-75 10/3/06 11:30 AM Page 74

75

postcontrast T1-weighted imaging in brain neoplastic disease. Figure 38–2 illustratesan age-matched comparison of (A, C) pre- and (B, D) postcontrast images acquired at1.5 and 3 T. Scan times were 3:44 (pre) and 5:02 (post), for a 5-mm slice, at 1.5 T ascompared with 1:11 (pre and post), for a 3-mm slice, at 3 T. Note the vascular pulsa-tion artifacts on the 1.5 T study, accentuated postcontrast (arrows), despite the use ofgradient moment nulling (flow compensation). No ghosting is evident on the 3 Tstudy. Thus, despite statements in the literature to the contrary, excellent T1-weight-ed images of the brain can easily be acquired at 3 T by use of short TE 2D GRE tech-nique, a critical point for tumor imaging.

Figure 38–2

Chapter 38_p74-75 10/3/06 11:30 AM Page 75