Technical developments for cerebral thermal treatment: water-cooled diffusing laser fibre tips and temperature-sensitive MRI using intersecting image planes.

The aim was to determine if water-cooled diffusing tips could produce larger and safer (better controlled) thermal lesions than non-cooled diffusing tips at 980 nm. Thermal lesions were induced in beef myocardium in vitro with and without water cooling using a 980 nm diode laser at various power levels. Seven intracerebral treatments were performed in six canines using water-cooled diffusing tips with four animals having intracerebral transmissible venereal tumours grown from inoculate. Magnetic resonance thermal imaging (MRTI)-based feedback software using a fast, radio frequency-spoiled gradient echo acquisition with two intersecting image planes was used for on-line monitoring and control of treatment and for the evaluation of in vivo laser lesion production. In cases where two-plane MRTI was employed, the maximum calculated temperature was compared in each plane. Using water-cooled tips and 400 micro m core diameter laser diffusing fibres in in vitro beef myocardium, power of up to 9.5 W was applied for 8 min without tip failure. Without cooling, tip failure occurred in under 4 min at 6 W, in under 2 min at 7 W and instantaneously at 8 W. Additionally, char accompanied lesions made with uncooled tips while cooled application resulted in only minimal char at only the highest thermal dose. Achieved lesion cross-sectional diameters in in vitro samples were up to 26.5 x 23.3 mm when water cooling was used. In canine brain and transmissible venereal tumours, up to 18.1 x 21.4 mm lesions were achieved. It is concluded that water cooling allows safe application of higher power to small core diameter diffusing tip fibres, which results in larger thermal lesions than can be achieved without cooling. Two-plane MRTI enhances on-line monitoring and feedback of thermal treatment.

Cooled-tip diode laser catheter for improved catheter ablation of ventricular tachycardia.

Catheter ablation for the treatment of arrhythmias has evolved dramatically over the past two decades. Researchers have investigated alternative energy sources and catheter constructs to improve the efficacy and safety of catheter ablation. This study tested the hypothesis that a new prototype cooled-tip laser catheter used with a low-power diode laser would improve catheter ablation of ventricular tachycardias. Four mongrel dogs underwent a median sternotomy. The cooled-tip laser catheter was advanced into the left ventricle via the left carotid artery and positioned adjacent to the endocardium. Laser powers of 3 and 4 W were delivered at four exposure times to select areas of the endocardium. During application of laser energy, room-temperature saline was circulated through the catheter. At necropsy the hearts were examined and fixed in formalin for histologic examination. Gross examination of the endocardial surfaces showed no indication of crater or thrombus formation. Cross-section of the lesions revealed sharply demarcated, circular-shaped areas of coagulative necrosis extending into the mid-myocardium. Areas of coagulative necrosis were identified within the myocardium extending into the mid-myocardium and occasionally the subepicardium. A sharp line of demarcation was observed between the lesions and the surrounding normal myocardium. The results of this study showed that we could use surface cooling during slow laser heating to create large subsurface lesions with characteristics appropriate for treatment of ventricular tachycardia and little to no surface damage. We believe our catheter system addresses many of the previous issues with laser-based approaches.

Simultaneous optical and nuclear magnetic resonance spectroscopy for monitoring cardiac energetics in vivo.

There are a number of applications in which it is useful to simultaneously collect data from what are traditionally separate instrumentation modalities. In particular, in vivo physiological investigations in which data from parallel experiments must be correlated would benefit from simultaneous data collection through 1) elimination of subject variability, 2) elimination of treatment variability, and 3) a reduction in the number of animal preparations required. Here we describe the simultaneous collection of fluo-3 optical fluorescence and 31P nuclear magnetic resonance (NMR) spectra to measure intracellular calcium levels and high-energy phosphate metabolism, respectively, in vivo. This work is part of ongoing research into the profound anoxia tolerance exhibited by the hearts of certain turtle species. An NMR compatible optical fluorescence spectrometer was constructed and tested. In the 31-cm bore of a 2 T superconducting magnet, NMR and optical spectra were collected every 10-15 min from the in situ, in vivo hearts of anesthetized turtle subjects prior to and during one to three hours of anoxia. It was found that while PCr stores became significantly depleted during anoxia, beta-adenosine triphosphate (ATP) levels remained within 20% of control values, and intracellular diastolic calcium levels did not vary by more than 10%. The ability to make simultaneous phosphorus and calcium measurements on a single subject is important to understanding the exact relationship between phosphorus energy state and maintenance of calcium homeostasis.

Optical glucose sensing in biological fluids: an overview.

Recent technological advancements in the photonics industry have led to a resurgence of interest in optical glucose sensing and to realistic progress toward the development of an optical glucose sensor. Such a sensor has the potential to significantly improve the quality of life for the estimated 16 million diabetics in this country by making routine glucose measurements more convenient. Currently over 100 small companies and universities are working to develop noninvasive or minimally invasive glucose sensing technologies, and optical methods play a large role in these efforts. This article reviews many of the recent advances in optical glucose sensing including optical absorption spectroscopy, polarimetry, Raman spectroscopy, and fluorescent glucose sensing. In addition a review of calibration and data processing methods useful for optical techniques is presented.