The effect of sacrifice on image signal, T1, T2, and T2∗ in liver, kidney, and brain of the Wistar rat

Signal intensity in SE24025 and GE24025 images, T2∗, T2, and T1 were measured prior to and after sacrifice at 1.5 T in liver, kidney, and brain of Wistar rats. Presacrifice, animals were maintained on 2–3% halothane, ensuring a high saturation of venous haemoglobin with oxygen, which emphasised blood oxygenation level dependent (BOLD) effects upon deoxygenation of haemoglobin postsacrifice. T2∗ values (in ms) changed on sacrifice from 27.8 ± 4.1 to 15.0 ± 1.1 in liver (p ⪡ .001), from 57.4 ± 6.5 to 52.8 ± 5.7 in brain (p < .02), and from 52.3 ± 10.3 to 37.6 ± 11.9 in kidney cortex (p < .01). T2∗ was also reduced in kidney medulla and papilla. T2 reduced on sacrifice (by a lesser amount than T2∗), except in brain, which showed a small increased T1 (ms) changed only in liver, showing a significant increase from 670 ± 31 to 834 ± 69 (p ⪡.001). The ratio of signal postsacrifice to presacrifice was lowest in the SE24025 and GE24025 images of liver (0.73 ± 0.03 and 0.52 ± 0.05, respectively), but increased T1 may account for some of these changes. Expected signal ratios at sacrifice calculated from measured relaxation times agreed well with those observed experimentally. Relaxation changes observed on sacrifice were consistent with deoxygenation of haemoglobin. These results give an estimate of the maximum effects which changes of blood oxygen level might produce at 1.5 T and suggest that contrast due to variation of endogenous deoxyhaemoglobin may be exploitable in the liver.