1H chemical shift imaging characterization of human brain tumor and edema

Longitudinal (T1) and transverse (T2) relaxation times of metabolites in human brain tumor, peritumoral edema, and unaffected brain tissue were assessed from point resolved spectroscopy (PRESS) (1)H chemical shift imaging results at different repetition times (TR=1500 and 5000 ms; T1: n=19) and echo times (TE=135 and 270 ms; T2: n=7). Metabolite T1 and T2 relaxation times in unaffected brain tissue corresponded with those published for healthy volunteers. T2 relaxation times were reduced in tumor (choline, N-acetyl aspartate) and edema (choline, creatine) compared with unaffected brain tissue ( p<0.02, each), whereas T1 relaxation times did not change significantly. Choline peak area was increased in tumor, creatine and N-acetyl aspartate were decreased in edema and tumor compared with unaffected brain tissue. Metabolite line widths were increased in tumor. It is concluded that under standard measurement conditions the metabolite profiles are not affected by differential T1 saturation. The short T2 of choline in tumor and edema implies that short-echo-time 1H chemical shift imaging is most suited in the use of choline elevation as tumor marker.