Biomedical subjects

John Tulip

Publications and source records attributed to John Tulip.

5 recordsLinked to original sources

PubMed2006

Pulsed quantum cascade laser-based cavity ring-down spectroscopy for ammonia detection in breath.

Breath analysis can be a valuable, noninvasive tool for the clinical diagnosis of a number of pathological conditions. The detection of ammonia in exhaled breath is of particular interest for it has been linked to kidney malfunction and peptic ulcers. Pulsed cavity ringdown spectroscopy in the mid-IR region has developed into a sensitive analytical technique for trace gas analysis. A gas analyzer based on a pulsed mid-IR quantum cascade laser operating near 970 cm(-1) has been developed for the detection of ammonia levels in breath. We report a sensitivity of approximately 50 parts per billion with a 20 s time resolution for ammonia detection in breath with this system. The challenges and possible solutions for the quantification of ammonia in human breath by the described technique are discussed.

Ammonia↗

PubMed2004

Light dosimetry for multiple cylindrical diffusing sources for use in photodynamic therapy.

Since prostatic carcinoma is usually multifocal within the prostate, effective photodynamic therapy (PDT) of prostatic carcinoma is expected to require the photochemical destruction of the entire organ. Accurate light dosimetry will be essential to avoid damage to proximal sensitive tissue such as the rectum. The prostate will be illuminated using interstitial cylindrical fibreoptic light sources and, because of the limited transparency of prostate tissue, these sources will be mounted in a parallel array analogous to the source array used in brachytherapy. Both source spacing and the light delivered to each source will control light dosimetry from a parallel array of fibreoptic sources implanted into tissue. Clinical PDT will require dose planning in order to determine the position and illumination of each source prior to treatment, but unfortunately few methods of predicting light fluence from cylindrical interstitial sources currently exist. In this paper, a novel light fluence model is used to predict tissue transillumination resulting from cylindrical interstitial sources. The cylindrical source is modelled as a finite array of infinitesimal small sources using Christian Huygens' famous single-slit diffraction model. We show that this source model when combined with a robust derivation of fluence in a spherical geometry using diffusion theory, accurately predicts fluence levels from a single cylindrical source in a variety of media. This method is found to retain its accuracy near the sources. With a simple extension, this fluence model is used to predict the light fluence levels from an array of three sources and the predicted fluence is found to compare favourably with experimental data.

Diffusion↗

PubMed2003

Whole bladder photodynamic therapy for orthotopic superficial bladder cancer in rats: a study of intravenous and intravesical administration of photosensitizers.

PURPOSE: Photodynamic therapy after intravenous injection of Photofrin (QLT Phototherapeutics, Vancouver, British Columbia, Canada) results in a contracted bladder and skin photosensitivity, which limits its clinical application. In an attempt to overcome these limitations photodynamic therapy after intravesical instillation of Photofrin or 5-aminolevulinic acid (ALA) in an orthotopic rat bladder tumor model was explored and compared with intravenous Photofrin for photodynamic therapy efficacy and phototoxicity. MATERIALS AND METHODS: At 2 weeks after bladder implantation of 1.5 x 10(6) AY-27 tumor cells animals were randomly grouped. Photofrin was administered (5 mg./kg. intravenously and 2 mg./ml. intravesically). The ALA concentration for intravesical instillation was 300 mM. Whole bladder photodynamic therapy with graded doses of light (lambda = 630 nm.) was performed 4 hours after drug administration. Tumor control and complications were evaluated. RESULTS: Photodynamic therapy with intravenous Photofrin plus 100 J./cm.(2) light resulted in severe bladder damage. Of 10 rats 6 died and 2 of the 10 that received 50 J./cm.(2) died. There were no photodynamic therapy related deaths in groups receiving intravesical instillation of Photofrin or ALA that also received 50 to 100 J./cm.(2) Median survival in rats treated with ALA intravesically plus 75 J./cm.(2) (77 days), Photofrin intravesically plus 50 (67) or 100 J./cm.(2) (76) and Photofrin intravenously plus 50 J./cm.(2) (60) were significantly different from that in controls (44). CONCLUSIONS: Intravesical instillation of Photofrin or ALA can achieve the same photodynamic therapy efficacy as intravenous Photofrin in this orthotopic rat bladder tumor model with less phototoxicity to normal tissues.

Administration, Intravesical↗

PubMed2003

Laser Doppler imaging of burn scars: a comparison of wavelength and scanning methods.

UNLABELLED: Laser Doppler perfusion imaging (LDI) is a useful tool for the early clinical assessment of burn depth and prognostic evaluation of injuries that may require skin grafting. We have evaluated two commercially available laser Doppler imagers for the perfusion measurement of normal and burn scar tissue. METHODS: A single wavelength (635 nm), step-wise scanning LDI and a dual wavelength (633 and 780 nm), continuous scanning LDI were used. Twenty patients with hypertrophic burn scars (time since injury: 1 month-8 years) were recruited and the color and elevation of the scar was clinically assessed using a modified Vancouver Burn Scar Scale. Perfusion of each scar region was measured using both imagers. A symmetric contralateral region of unburned skin was also imaged to record baseline perfusion. RESULTS: Comparisons of wavelength and scanning technique were made using perfusion values obtained from 22 burn scars. Highly significant positive correlation was observed in all comparisons. In addition, output from both instruments was strongly and significantly correlated with the clinical grading of the scar. SIGNIFICANCE: Both LDI scanners perform similar perfusion measurements. The results also indicate that red and near-infrared (NIR) wavelength photons provide similar blood flow information. The faster, continuous scanning method provides a clinical advantage without a significant loss of blood flow information. However, a critical evaluation of both instruments suggests that caution must be exercised when using these optical diagnostic techniques and that some knowledge of light-tissue interaction is required for the proper analysis and interpretation of clinical data.

Adult↗

PubMedDate not supplied

Interstitial photodynamic therapy in subcutaneously implanted urologic tumors in rats after intravenous administration of 5-aminolevulinic acid.

Photodynamic therapy (PDT) may be an attractive option for treatment of early stage prostate cancer. Aminolevulinic acid (ALA) acts as a prodrug leading to a selective accumulation of a photosensitizer, protoporphyrin IX (PpIX), in epithelial cells. We investigated the efficacy of ALA-mediated PDT for rat R3327-H prostate cancer, compared with the AY-27 bladder tumor. Rats bearing either AY-27 or R3327-H tumors were randomized to different groups when their tumors reached approximately 1000 mm3. At the day of PDT, animals were administered 500 mg/kg ALA intravenously 4 hours prior to laser therapy. The argon-pumped dye laser light (630 nm) was coupled to multiple quartz fibers with cylindrical diffusing tips, which were inserted into the tumor in icosahedral pattern. Light exposure was varied to yield doses of 1000 to 3000 J/tumor. Animals bearing R3327-H tumors were imaged with 99mTc-HMPAO scintigraphy to evaluate tumor perfusion changes induced by PDT. There was a light-dose dependent tumor response in both tumor models. The mean time for R3327-H tumor to re-grow to 4 x treatment volume was 79.7 days in the control group (light only), 159 days in 1000 J group, and 169 days in 2000 J group (P < 0.05). Tumors treated with 3000 J were clinically cured (P < 0.01). Likewise, for AY-27 tumors, the average time to re-grow to 4 x treatment volume was 13.7 days in the control group, 179.3, 183.3, and 185.7 days in groups of 1000, 1500, and 2000 J (P < 0.05), respectively. Tumors treated with 3000 J were clinically cured (P < 0.01). 99mTc-HMPAO scintigraphy demonstrated a mild perfusion impairment following PDT. Interstitial PDT with ALA/PpIX is equally effective in treating prostate cancer and TCC in these heterotopic rat models.

Adenocarcinoma↗