MR thermometry characterization of a hyperthermia ultrasound array designed using the k-space computational method

BACKGROUND: Ultrasound induced hyperthermia is a useful adjuvant to radiation therapy in the treatment of prostate cancer. A uniform thermal dose (43°C for 30 minutes) is required within the targeted cancerous volume for effective therapy. This requires specific ultrasound phased array design and appropriate thermometry method. Inhomogeneous, acoustical, three-dimensional (3D) prostate models and economical computational methods provide necessary tools to predict the appropriate shape of hyperthermia phased arrays for better focusing. This research utilizes the k-space computational method and a 3D human prostate model to design an intracavitary ultrasound probe for hyperthermia treatment of prostate cancer. Evaluation of the probe includes ex vivo and in vivo controlled hyperthermia experiments using the noninvasive magnetic resonance imaging (MRI) thermometry. METHODS: A 3D acoustical prostate model was created using photographic data from the Visible Human Project(®). The k-space computational method was used on this coarse grid and inhomogeneous tissue model to simulate the steady state pressure wavefield of the designed phased array using the linear acoustic wave equation. To ensure the uniformity and spread of the pressure in the length of the array, and the focusing capability in the width of the array, the equally-sized elements of the 4 × 20 elements phased array were 1 × 14 mm. A probe was constructed according to the design in simulation using lead zerconate titanate (PZT-8) ceramic and a Delrin(® )plastic housing. Noninvasive MRI thermometry and a switching feedback controller were used to accomplish ex vivo and in vivo hyperthermia evaluations of the probe. RESULTS: Both exposimetry and k-space simulation results demonstrated acceptable agreement within 9%. With a desired temperature plateau of 43.0°C, ex vivo and in vivo controlled hyperthermia experiments showed that the MRI temperature at the steady state was 42.9 ± 0.38°C and 43.1 ± 0.80°C, respectively, for 20 minutes of heating. CONCLUSION: Unlike conventional computational methods, the k-space method provides a powerful tool to predict pressure wavefield in large scale, 3D, inhomogeneous and coarse grid tissue models. Noninvasive MRI thermometry supports the efficacy of this probe and the feedback controller in an in vivo hyperthermia treatment of canine prostate

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Ontogenic development of steroid 16 alpha-hydroxylase as a tool for the study of the multiplicity of cytochrome P-450.

peer reviewedaudience: researcher, professional1. Activities of progesterone, testosterone, pregnenolone and dehydroepiandrosterone 16 alpha-hydroxylase are undetectable in the fetal rat liver. During the neonatal period, the four enzymic activities increase in parallel to the concentration of cytochrome P-450. Until puberty, they develop similarly in male and female rat livers. From the 40th to the 55th day, the four steroid 16 alpha-hydroxylase activities increase rapidly in the male rat liver. The sexual differentiation of the steroid 16 alpha-hydroxylation observed in adult male and female rats takes place around the 55th day. 2. In the adult rat liver, steroid 16 alpha-hydroxylase is supported by two forms of cytochrome P-450 (form I and form II), which differ in their relative affinities for the various steroid substrates, and by their relative proportions in male and female rat livers. These two forms of cytochrome P-450 are also present in the young male and female rat livers, but are roughly equal in proportion. The transition from the immature to the adult repartition of the two forms occurs during puberty and is correlated with the sexual differentiation of the steroid 16 alpha-hydroxylase activities. 3. During the critical phases of the rat ontogenic development, the in vitro interactions between benzo[a]pyrene and steroids were compared at the level of two rat liver monooxygenases: steroid 16 alpha-hydroxylase and aryl hydrocarbon hydroxylase. (a) In the immature male and female rat livers, progesterone 16 alpha-hydroxylase, and to a lesser extent, pregnenolone 16 alpha-hydroxylase are inhibited by benzo[a]pyrene. Progesterone 16 alpha-hydroxylase is also inhibited by metyrapone. (b) In the young rat, aryl hydrocarbon hydroxylase cannot be inhibited by steroids and appears to be supported by a single form of cytochrome P-450. The transition from the immature to the adult situation occurs around the 40th day