Christian Sturesson

A mathematical model for predicting the temperature distribution in laser-induced hyperthermia. Experimental evaluation and applications

A time-dependent mathematical model for the heat transfer in laser-induced hyperthermia has been developed. The model calculates the temperature distribution in surface-irradiated tissues. Good agreement was found between the predictions of the model and in vitro experimental results obtained for bovine liver irradiated with an expanded beam from a Nd:YAG laser. Surface evaporation of water was included in the model and experimentally verified. The discrepancy between the measured and the calculated rise in temperature at three different depths on the axis of symmetry of the irradiating beam was found to be less than 5% after 15 min of irradiation. When irradiating in air and not accounting for the surface evaporation in the model, the accuracy of the model predictions was only 75-80%. The model was then used to investigate the influence of surface evaporation of water on the total temperature distribution theoretically in a clinically relevant case. From the numerical simulations, it was shown that, simply by providing a moistened liver surface, the maximum steady-state temperature could be forced into the tissue to a depth of 4 mm. It was also shown that, by employing the numerical model during the initial phase of hyperthermia treatment, overshooting of the temperature during the transient thermal build-up time could be prevented.

Mathematical modelling of dynamic cooling and pre-heating, used to increase the depth of selective damage to blood vessels in laser treatment of port wine stains

Based on the assumption that the maximum irradiance allowed during laser treatment of port wine stains is limited by the temperature rise at the dermoepidermal junction, we theoretically investigated how much the irradiance could be increased by dynamically cooling the skin surface. The heat condution equation was solved numerically in cylindrical coordinates using a skin model composed of four layers. The laser-light absorption was calculated using Monte Carlo simulations. The transient thermal behaviour of the skin was modelled when cooling with water at a temperature of 0 degrees C and with liquid nitrogen at a temperature of -196 degrees C. With cooling, an increase in the maximum irradiance by a factor of 2.3-3.6 was theoretically permitted depending on the irradiation time, wavelength and mode of cooling. The corresponding increase in vessel selective damage depth was predicted to be 0.4-0.5 mm. A new concept for increasing the depth of vessel selective damage is introduced where the initial temperature profile of the skin is reshaped by using not only surface cooling but also laser irradiation. By pre-irradiating the skin with near-infrared light without selective absorption by the tissue chromophores in conjunction with surface cooling, a maximum temperature at a depth of 1 mm from the dermoepidermal junction was theoretically achieved. A subsequent 0.1 s pulse from a frequency doubled Nd:YAG laser is theoretically shown to selectively destroy vessels up to a depth of 0.8 mm from the dermoepidermal junction. By pre-heating at 1064 nm and treating at 532 nm in conjunction with surface cooling, the theoretical results indicate that the Nd:YAG laser can compete in effectiveness with the flashlamp-pumped dye laser in the treatment of port wine stains.

Feedback interstitial diode laser (805 nm) thermotherapy system: Ex vivo evaluation and mathematical modeling with one and four-fibers

In this study a newly developed microprocessor controlled power regulation and thermometry system integrated with a diode laser (805 nm wavelength) was evaluated with respect to temperature distribution, effectiveness of regulation, and ability to predict temperature distributions by computer simulation.

Prolonged chemotherapy impairs liver regeneration after portal vein occlusion – An audit of 26 patients

AIM The aim of the present retrospective study was to investigate the influence of neoadjuvant chemotherapy on liver regeneration after portal vein occlusion before major hepatectomy. METHOD Between 2003 and 2007, 26 patients underwent portal vein occlusion, of whom 22 had portal vein embolisation and 4 portal vein ligation. 15 of 23 patients with colorectal liver metastases had neoadjuvant chemotherapy. RESULTS After portal vein occlusion, the ratio of the future liver remnant volume to total parenchymal liver volume (FLR%) was reduced in patients receiving neoadjuvant chemotherapy (27 +/- 1% vs 32 +/- 1%, p = 0.03). A smaller future liver remnant before portal vein occlusion resulted in a greater degree of hypertrophy (r(2) = 0.18, p = 0.04). Patients with tumour size greater than 60 mm showed a decreased degree of hypertrophy (7 +/- 1)% as compared to patients with smaller tumours (13 +/- 1%, p = 0.01). There was one death shortly after portal vein embolisation. 19/26 patients were resected with zero operative mortality. CONCLUSION Prolonged neoadjuvant chemotherapy has a small negative effect on liver regeneration induced by portal vein occlusion. Liver regeneration induced by portal vein occlusion is relatively large when tumour burden is small.

Interstitial laser-induced thermotherapy: Influence of carbonization on lesion size

The size of laser‐induced coagulated lesions produced in porcine muscle in vitro using a cylindrical diffusing fiber tip and a conductive heat source, made by covering the diffuser with a hollow steel needle, were compared to investigate the influence of charring.

Tumour vessel damage resulting from laser-induced hyperthermia alone and in combination with photodynamic therapy

This study examined tumour vessel injury resulting from laser-induced hyperthermia alone and in combination with photodynamic therapy (PDT) in the treatment of rat liver tumours by means of scanning electron microscopy. A total of 18 Wistar rats were divided into three groups. Group I (six animals) underwent hyperthermia for 15 min (15-min hyperthermia). Group II (six animals) underwent hyperthermia for 30 min (30-min hyperthermia). Group III (six animals) received the combined treatment of PDT and 30-min hyperthermia. For PDT, delta-amino laevulinic acid at a dose of 60 mg/kg of body weight was intravenously administered 60 min before irradiation at 635 nm. The morphological results indicated that 15-min hyperthermia gave rise to an increase in permeability of the vessels in the treated tumour. Thirty-min hyperthermia caused extreme oedema of vascular endothelial cells and restrictive openings of tumour branch vessels. The combined therapy of PDT and hyperthermia destroyed tumour vasculature. Large breaks of the inner wall of the treated tumour vessels were deeply involved in the basement membrane of the vessel. The results indicate that there may be a close link between inhibition of tumour growth and degree of damage to tumour vessels.

Non-invasive imaging of microcirculation: a technology review.

Microcirculation plays a crucial role in physiological processes of tissue oxygenation and nutritional exchange. Measurement of microcirculation can be applied on many organs in various pathologies. In this paper we aim to review the technique of non-invasive methods for imaging of the microcirculation. Methods covered are: videomicroscopy techniques, laser Doppler perfusion imaging, and laser speckle contrast imaging. Videomicroscopy techniques, such as orthogonal polarization spectral imaging and sidestream dark-field imaging, provide a plentitude of information and offer direct visualization of the microcirculation but have the major drawback that they may give pressure artifacts. Both laser Doppler perfusion imaging and laser speckle contrast imaging allow non-contact measurements but have the disadvantage of their sensitivity to motion artifacts and that they are confined to relative measurement comparisons. Ideal would be a non-contact videomicroscopy method with fully automatic analysis software.

Fast-track programmes for hepatopancreatic resections: where do we stand?

BACKGROUND Fast-track (FT) programmes represent a series of multimodal concepts that may reduce surgical stress and speed up convalescence after surgery. The aim of this systematic review was to evaluate FT programmes for patients undergoing hepatopancreatic surgery. METHODS PubMed, Embase and the Cochrane Library databases were searched for studies of FT vs. conventional recovery strategies for liver and pancreatic resections. RESULTS For liver surgery, three cohort studies were included. Primary hospital stay was significantly reduced after FT care in two of the three studies. There were no significant differences in rates of readmission, morbidity and mortality. For pancreatic surgery, three cohort studies and one case-control study were included. Primary hospital stay was significantly shorter after FT care in three out of the four studies. One study reported a significantly decreased readmission rate (7% vs. 25%; P= 0.027), and another study showed lower morbidity (47.2% vs. 58.7%; P < 0.01) in favour of the FT group. There was no difference in mortality between the FT and control groups. CONCLUSIONS FT rehabilitation for liver and pancreatic surgical patients is feasible. Future investigation should focus on optimizing individual elements of the FT programme within the context of liver and pancreatic surgery.

Pancreatic cancer : Yesterday, today and tomorrow

Pancreatic cancer is one of our most lethal malignancies. Despite substantial improvements in the survival rates for other major cancer forms, pancreatic cancer survival rates have remained relatively unchanged since the 1960s. Pancreatic cancer is usually detected at an advanced stage and most treatment regimens are ineffective, contributing to the poor overall prognosis. Herein, we review the current understanding of pancreatic cancer, focusing on central aspects of disease management from radiology, surgery and pathology to oncology.

Tissue temperature control using a water-cooled applicator: Implications for transurethral laser-induced thermotherapy of benign prostatic hyperplasia

A prototype to a water-cooled applicator to be used in transurethral laser-induced thermotherapy of benign prostatic hyperplasia was developed. The flexible applicator was made of Teflon tubes except for the distal outer part which was made of glass, providing a transparent medium for laser radiation and enabling efficient cooling of the surrounding tissue. For heating, laser light from a Nd:YAG laser emitting at 1064 nm, which was coupled into an optical fiber with an institutionally made diffusing tip, was used. Cooling was performed by flushing water through the applicator. By using a mathematical model it was possible to connect the temperature rise of the water in the applicator to the maximum tissue temperature. Tissue light absorption was calculated using Monte Carlo simulations and the heat conduction equation was solved numerically using a finite-difference technique. Experiments on porcine liver in vitro showed that the maximum tissue temperature could be estimated with an average accuracy of 0.4 degree C by measuring the difference in outlet and inlet applicator water temperature and using the thermal model. The results presented suggest that the described method for temperature control can be used during laser prostatectomy to maximize the lesion size while preventing carbonization.