Hemodynamics in rat liver tumor model during retrograde-outflow isolated hepatic perfusion with aspiration from the portal vein: angiography and in vivo microscopy.

BACKGROUND: Orthograde percutaneous isolated hepatic perfusion (IHP) techniques using balloon occlusion catheters are relatively simple and facilitate repeated therapy, but they result in higher rates of leakage from the perfusion circuit into the systemic circulation. Therefore, a feasible protocol for percutaneous IHP with less leakage is required. PURPOSE: To investigate hemodynamic changes in rat liver and tumor during retrograde-outflow isolated hepatic perfusion (R-IHP) with aspiration from the portal vein (PV). MATERIAL AND METHODS: Animal experiments were approved by the Animal Experiment Ethics Committee of Lund University. Eighteen rats underwent R-IHP after laparotomy and catheterization of the PV and hepatic artery (HA). The HA, inferior vena cava (IVC), and PV were ligated, and flow through the suprahepatic IVC was controlled with a suture loop. The rats were divided into two groups to examine blood flow during R-IHP. Four rats (group 1) underwent arteriography via the HA with and without R-IHP, and 14 rats (group 2) were inoculated with tumor and examined by in vivo fluorescence microscopy of liver and tumor during R-IHP. RESULTS: In group 1, hepatic arteriography during R-IHP confirmed arterioportal communication in all four rats, with the PV acting as an outflow tract. In vivo fluorescence microscopy in group 2 showed strong enhancement of tumors, and no blood supply from the portal venules to the tumors was seen in any of the 14 rats. Blood flow in the major portion of the hepatic lobules was stopped and the percentage of enhanced area was significantly lower in the normal hepatic lobules than in the tumors (P < 0.0001). CONCLUSION: We confirmed reversal of blood flow concomitant with good perfusion of the liver tumor and with reduced perfusion of normal liver parenchyma during R-IHP.

Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling.

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm(3). Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15-20 min. Mean brain temperature reduction varied in the interval <-3.0; -0.6>°C and <-2.7; -0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.

Noninvasive monitoring of brain temperature during mild hypothermia.

The main purpose of this study was to verify the feasibility of brain temperature mapping with high-spatial- and reduced-spectral-resolution magnetic resonance spectroscopic imaging (MRSI). A secondary goal was to determine the temperature coefficient of water chemical shift in the brain with and without internal spectral reference. The accuracy of the proposed MRSI method was verified using a water and vegetable oil phantom. Selective decrease of the brain temperature of pigs was induced by intranasal cooling. Temperature reductions between 2 degrees C and 4 degrees C were achieved within 20 min. The relative changes in temperature during the cooling process were monitored using MRSI. The reference temperature was measured with MR-compatible fiber-optic probes. Single-voxel (1)H MRS was used for measurement of absolute brain temperature at baseline and at the end of cooling. The temperature coefficient of the water chemical shift of brain tissue measured by MRSI without internal reference was -0.0192+/-0.0019 ppm/degrees C. The temperature coefficients of the water chemical shift relative to N-acetylaspartate, choline-containing compounds and creatine were -0.0096+/-0.0009, -0.0083+/-0.0007 and -0.0091+/-0.0011 ppm/degrees C, respectively. The results of this study indicate that MRSI with high spatial and reduced spectral resolutions is a reliable tool for monitoring long-term temperature changes in the brain.

A new method of selective, rapid cooling of the brain: an experimental study.

PURPOSE: To determine whether retrograde perfusion of cooled blood into one internal jugular vein (IJV) in the pig can selectively reduce the brain temperature without affecting the core body temperature (CBT). METHODS: In 7 domestic pigs, the left IJV was catheterized on one side and a catheter placed with the tip immediately below the rete mirabile. Thermistors were placed in both brain hemispheres and the brain temperature continuously registered. Thermistors placed in the rectum registered the CBT. From a catheter in the right femoral vein blood was aspirated with the aid of a roller pump, passed through a cooling device, and infused into the catheter in the left IJV at an initial rate of 200 ml/min. RESULTS: Immediately after the start of the infusion of cooled blood (13.8 degrees C) into the IJV, the right brain temperature started to drop from its initial 37.9 degrees C and reached 32 degrees C within 5 min. By increasing the temperature of the perfusate a further drop in the brain temperature was avoided and the brain temperature could be kept around 32 degrees C during the experiment. In 4 of the animals a heating blanket was sufficient to compensate for the slight drop in CBT during the cooling period. CONCLUSIONS: We conclude that brain temperature can be reduced in the pig by retrograde perfusion of the internal jugular vein with cooled blood and that the core body temperature can be maintained with the aid of a heating blanket.