fig 2.

Dynamic T1-weighted fast field echo coronal section of the anterior brain, obtained during the first freezing cycle. The imaging duration was 4 seconds. The inactive cryoprobe appears signal free and causes no artifacts (upper row, left). After passing cryogen through the probe (from left to right), a signal-free and spherically shaped ice ball forms around the probe tip. Excellent ice:tissue contrast (91%, mean signal intensity of the ice, 90.7 ± 21.6; mean signal intensity of the unfrozen brain, 1032.5 ± 135.6). Note the hyperintense rim around the signal-free ice, which follows the growing and thawing ice formation and is assumed to represent the temperature gradient of the cooled but unfrozen tissue. Signal increase of the ice is seen during thawing (lower row, middle)