| Part 1Experimental study of change regularity of tissuetemperature during laser-induced interstitialthermotherapy in liver Objective: The purpose of this study was to evaluate change regularity of tissue temperature during laser-induced interstitial thermotherapy in liver. Materials and methods: Five New Zealand white rabbits (mean 3.81 Kg) were anesthetized using intravenous 3% barbital sodium (1ml/Kg). After preserved skin, a laparotomy was performed along the right sub-costal part of rabbit in order to exposure liver. An 18-gauge aspiration needle was inserted into liver by a self-made puncture frame, a 600 u m diameter of optical fiber was introduced and connected with GaAlAs semiconductor laser applicator (Diamed, UK). Four thermistor probes (18-gauge) were respectively placed 5mm, 7mm, 9mm, 11 mm from the tip of fiber by puncture frame, and the probes parallel to the puncture needle. The probes were connected with the MR-compatible thermometry system (TDS 0800-1, Shandong provincial medical imaging research institute) and starting software for thermometry. Laser applications were performed at 5W with continuous mode during 660s in all of animal livers, and the totalenergy was 3300J. After ablations and the livers were cooling to the pre-operative temperature, the rabbits were sacrificed using a barbiturate overdose technique and the livers were removed. The specimens were cut along the plane consisted of the long axes of the puncture needle and four probes, and measured the maximum diameter of lesion on the plane, the line of measurement perpendicular to the long axes of needles. The temperature date saved by computer was extracted and the temperature change was analyzed with the SPSS 10.0 statistical software package. Results: On gross examination, lesions demonstrated 4 zones from inner to outer: the first zone was the vaporized empty cavity (mean 2.6 mm, 2.0mm -3.0 mm) surrounding the tip of optical fiber; a thin rim of black carbonized tissue (mean 5.2mm, 5.0 mm~6.0 mm) lining the cavity wall was the second zone; the third zone was the yellow and white area of coagulated necrosis (mean 14.6 mm, 14.0mm~15.0 mm); the brownish ring of homorrhage and hyperemia (mean 19.6 mm, 18.0 mm~22.0mm) surrounding the necrosis area was the forth zone; the outermost tissue appeared histologically normal. The scattering small gas bubbles were seen in the carbonized and coagulated tissue, a little black carbonized tissue could be seen in the coagulated tissue zone. The differences of temporal temperature gradients recorded by four probes were statistically significant ( x 2=27.764, P=0, P<0.05; x2=19.177, P=0, P<0.05); and the differences of spatial temperature gradients between probes were statistically significant ( x =30.382, P=0, P<0.05). The ascending curve of temperature demonstrated an ascending parabola shape, and the curve gets the flatter, the farther probe is from optical fiber. The temperature raised rapidly in the early stage of ablation, and the rate of temperature rising was decreased gradually as time went on, the temporal temperature gradient demonstrated descending trend. The descending curve of temperature demonstrated an inverse parabola shape, and the curve gets the flatter,the farther probe is from optical fiber. The temperature fell rapidly in the early stage of cooling, and the rate of temperature fall was decreased gradually as time went on, the temporal temperature gradient demonstrated descending trend. The spatial temperature gradient demonstrated ascending trend, the gradient increased gradually as time went on, and achieved peak as ablation stopping (mean 4.5460°C /mm); furthermore, and the spatial temperature gradient gets the smaller, the farther probe is from fiber. Conclusions: During LITT of liver, the temperature change of injury tissue existed some extent of regularity, however, there were obviously individual differences in the aspect of temperature curve, temporal and spatial temperature gradient. Part 2:Experimental study of interventional MRI-guided laser-induced interstitial thermotherapy in liver Objective: The purpose of this experimental study was to evaluate the feasibility of IMRI-guided LITT in liver and MRI-pathologic correlation of ablation lesion. Materials and methods: Sixteen New Zealand white rabbits (mean 3.69 Kg) were divided 2 groups randomly, 8 rabbits each group, after anesthetized and preserved skin, the rabbits were supine on the table of low field open configuration interventional MRI (0.23 T, Proview, Philips). Under guidance of optical navigating system (iPath 200, Proview, Philips), an aspiration needle and a thermistor probe were inserted into liver, an optical fiber was introduced through the needle, the probe parallel to the needle, and the tip of probe was placed 5-10 mm from the tip of fiber. Starting MR-compatible thermometry system (TDS 0800-2, Shandong provincial medical imaging research institute). The fiber connected with GaAlAs semiconductor laser applicator (Diamed, UK), and laser applications were performed at 5W with continuous mode. After ablations and the livers were cooling to the pre-operative temperature, multi-sequences (FE-3D, CBASS-3D, SE T1WI, FSE T2WI) MR examination were performed, then the maximum diameter of lesion with hypo-signal was measured on the image of center slice. After the rabbits were sacrificed, the maximum diameter of various lesions was measured macroscopically on the plane corresponding with MR slice. After measurement, one sample of each group was sent for electronic microscopy examination and others were sent for optical microscopy examination of HE stain. The experimental date was analyzed with theSPSS 10.0 statistical software package. Results: All punctures of liver were completed smoothly under guidance of MRI (16/16). On the images of FE-3D, CBASS3D and SE sequences, the lesions demonstrated obviously hypo-signal surrounded by normal liver signal. On the images of FSE T2WI sequence, the most of lesions demonstrated hypo-signal (13/16) with peripheral thin rim of hyper-signal surrounded by normal liver signal; some of lesions showed a central hyper-signal area (3/16) with a peripheral hypo-signal zone and surrounded by normal liver signal. Comparing the gross examination, the centrally bright signal was due to the central empty cavity filled with hyper-intense serum. The mean diameter of vaporized zone (Da) was 3.125 mm (2 mm~4 mm); that of carbonized zone (Dt>) was 6.188 mm (4 mm~8 mm); that of coagulated zone (Dc) was 16.188 mm (10 mm~22 mm); that of homorrhage and hyperemia zone (Da) was 20.875 mm (16 mm~30 mm); the diameter of Dfe was 6.862 mm (4.2 mm~10.6 mm); that of Dcbass was 6.731 mm (3.9 mm~9.7 mm); that of Dse was 9.519 mm (4.8 mm~12.6 mm); that of Dfse was 16.150 mm (8.8 mm~23.4 mm). The difference between Dfse and Dc was not statistically significant (P=0.97, P>0.05) and Dfse correlated closely with Dc (r=0.977, P<0.01); the difference between DFe and Db was not statistically significant (P=0.581, P>0.05), DFE correlated with Db (r=0.659 , P<0.01); the difference between Dfe and Dcbass was not statistically significant (P=0.894, P>0.05). The energy of LITT correlated with Dc (r=0.821, P<0.01). Conclusions: Interactive optical navigating MRI can effectively guide placement of optical fiber and accurately measure the size of thermal ablation, improve the safety and accuracy of LITT. Part 3Experimental study of time-temperature thresholds-controlled laser-induced interstitial thermotherapy in liver Objective: The purpose of this study was to evaluate the feasibility of using time-temperature thresholds to control LITT of liver. Materials and methods: Sixteen New Zealand White rabbits (mean 3.69 Kg) were divided 2 groups randomly, 8 rabbits each group, after anesthetized and preserved skin, the rabbits were supine on the table of low field open configuration interventional MRI (0.23 T, Proview, Philips). Under guidance of optical navigating system (iPath 200, Proview, Philips), an aspiration needle and a thermistor probe were inserted into liver, an optical fiber was introduced through the needle, the probe parallel to the needle, and the tip of probe was placed 5-10 mm from the tip of fiber. Starting MR-compatible thermometry system (TDS 0800-2, Shandong provincial medical imaging research institute), setting the auto alarm of time-temperature and recording temperature. The fiber connected with GaAlAs semiconductor laser applicator (Diamed, UK), and laser applications were performed at 5W with continuous mode. The group 1 stopped ablation until the temperature reached 60°C; and the group 2 stopped ablation as soon as the time-temperature thresholds achieved. After ablations and the livers were cooling to the pre-operative temperature, cut off the powers of laser applicator and thermometry system. After the rabbits were sacrificed, the distance (Dl) from the tip of optical fiber to the tip of probe was measured on the plane consisted of the long axes of needle and probe, and the distance (D2) from the tip of optical fiber to the outermost margin of the coagulated necrosis was measured along theabove measurement line. After measurement, one sample of each group was sent for electronic microscopy examination and others were sent for optical microscopy examination of HE stain in order to determine whether the liver tissue around the tip of probe was completely necrosis. The experimental date was analyzed with the SPSS 10.0 statistical software package. Results: The vaporized zone demonstrated empty cavity surrounding the tip of optical fiber. The carbonized zone did not properly stain with HE, it appeared as disorganized black, gold, or blue acellular carbonized tissue and showed complete coagulated necrosis with tissue shrinkage and disruption of lobular architecture lining the cavity wall. The coagulated necrosis zone demonstrated hepatic cell was obviously deformed, the shape of cell was lengthened, the nuclei showed long ellipse, the arrangement of cells were still regular, all of those were the findings of severe injury and complete necrosis of hepatic cell, it is especially obvious on the periphery area of hepatic lobule. The hepatic cellular chains were break off and the hepatic cells were dispersed. The zone of homorrhage and hyperemia demonstrated paler stain and looser texture of hepatic parenchyma, the regional cellular swollen and vacuolar formation of plasma were seen, the hepatic sinusoids were slightly dilated and hyperemia, a few inflammatory cells were seen in sinusoid and showed regional homorrhage. The outermost tissue appeared histologically normal. Electron microscopic studies showed cellular debris, disruption of hepatocytic cell membrane, chromatin condensation, extracellular lipid vacuoles, and swollen endoplasmatic reticula. All samples of 2 groups (16/16) demonstrated coagulated necrosis of hepatic tissue surrounding the tip of probe. The most common threshold temperature was 54 °C (6/16, 37.5%), the secondary was 52°C (4/16, 25%) and 56°C (3/16, 18.75%), 49 °C , 50 °C and 51 °C was seen in a rabbit (6.25%) respectively. In group 1: the mean of Dl was 7.112 mm (5.0 mm~8.5mm); that of D2 was 8.462 mm (7.0 mm~10.0 mm), the difference between Dl and D2 was statistically significant (P=0.031, P<0.05). In group 2: the mean of Dl was 7.762 mm (6.5 mm~10.0 mm); that of D2 was 8.737 mm (6.5 mm~ll mm), the difference between Dl and D2 was not statistically significant (P=0.068, P<0.05). In group 1, the mean of consumed time achieving 60°C was 624.63 s (150 s~2000 s); the mean of consumed energy was 3123.13 J (750 J-10000 J); the mean of consumed time achieving time-temperature thresholds was 344.38 s (132 s~550 s); the mean of saved time was 280.25 s (18 s~1487 s); the mean of consumed energy achieving time-temperature thresholds was 1721.88 J (660 J -2750 J); the mean of saved energy was 1401.25 J (90 J -7435 J). The mean percentage of saved time (or energy) was 26.63 %. The differences between Teot; and T m ?, E^ox: and E ?e were statistically significant (P=0.012 , P<0.05). Conclusions:Time-temperature thresholds-controlled LITT can completely ablate hepatic tissue, save time and energy of ablation, decrease the injury of normal tissue and increase the expected size of ablation.
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