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J A Case

Publications and source records attributed to J A Case.

6 recordsLinked to original sources
PubMed2000

Defining the heating characteristics of ferromagnetic implants using calorimetry.

The induction heating of small, cylindrical ferromagnetic implants for localized tumors is currently under investigation. These thermal rods are implanted within a lesion in 1 cm(2) arrays and subsequently exposed to an externally applied alternating magnetic field. Implants absorb energy from the field and transfer it as heat to the surrounding tissue. To achieve a uniform temperature rise throughout the tissue volume and to account for any field-rod misalignment, 400 mW of power per implant is used as the design specification. The temperature to necrose cells must be greater than 46 degrees C. A calorimeter was constructed to confirm that the rod power output specification is satisfied at temperatures adequate for inducing cell death. The rods were designed to undergo a ferromagnetic to paramagnetic transition at temperatures of 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C; this transition produces rods that are temperature self-regulating. Calorimetric results demonstrated that 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C rods provided 400 mW at 47-51 degrees C, 51-53.5 degrees C, 57 degrees C, and 62.5-63.5 degrees C, respectively. Thermal rods provide sufficient power output at the temperatures necessary to cause thermal ablation of tumors. The higher-temperature rods give a greater margin to ensure that necrotizing temperatures can be achieved throughout the rod array even with minor misalignment.

Algorithms↗
PubMed1999

Bone SPECT of the spine: a comparison of attenuation correction techniques.

UNLABELLED: Image artifacts from variable self-attenuation are recognized as major sources of diagnostic uncertainty in SPECT. For myocardial perfusion studies, an attenuation map is often obtained from a separate transmission study. However, for many applications such as bone SPECT, it has been believed to be unnecessary to obtain a transmission study to correct for the effects of attenuation. We have had significant success in clinical management of lower spine pain using bone SPECT. This success has led us to consider SPECT for the management of cervical spine pain. Cervical spine reconstructions without attenuation correction are difficult to interpret, because the high attenuation in the mandible and skull tends to decrease estimates of activity of the upper cervical spine, and the lower cervical/upper thoracic vertebrae are obscured by the shoulders. We present a technique that uses downscatter to provide attenuation correction for these acquisitions and compare it with other recognized attenuation correction techniques. METHODS: An emission study is acquired using two windows: one for obtaining the photopeak data and another for obtaining the downscattered photons. A body outline is estimated from these datasets using a projection data thresholding method. From this outline, a uniform attenuation map is created using attenuation coefficients appropriate for 99mTc in water (0.154 cm(-1)). These maps are used in SPECT reconstruction using ordered-subset expectation maximization (OSEM). This method is compared with (a) no attenuation correction (NC), (b) conventional Chang attenuation correction based on the interactive determination of the body outline from the 99mTc emission photopeak data (ChangAC) and (c) OSEM correction using attenuation maps estimated with a line source and fanbeam collimators (transAC). RESULTS: Patient studies using scatterAC demonstrated a significant improvement in the uniformity of estimated cervical spine uptake in normal patients, compared with either NC or ChangAC. Results using scatterAC were similar to those of transAC. We also observed significant improvement in uniformity using scatterAC in SPECT of the lower back in obese patients, as well as the relative limitations of scatterAC versus nonuniform, transmission-based attenuation correction. CONCLUSION: Comparisons with reconstructions using transmission data for estimating attenuation demonstrate that reasonable quantitative accuracy can be obtained in SPECT of the cervical spine using this simple attenuation estimate. Both scatterAC and transAC appear to provide consistent and expected uniform spine uptake in the cervical spines of normal patients.

Algorithms↗
PubMed1998

Development of the optical waveguide solar lighting system for space-based plant growing.

This article summarizes the study on the Optical Waveguide (OW) Solar Lighting System for space-based plant growing. In the OW solar lighting system, solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the OW transmission line consisting of low-loss optical fibers. The OW line transmits the solar radiation to the plant growing units where the solar radiation from the optical fibers is defocused and directed to the plants for optimum intensity for plant growing. In this study, the laboratory OW solar lighting system was constructed and tested for plant growth. The OW system consists of: 1) tracking reflective concentrators; 2) the optical waveguide transmission line; and 3) the plant lighting device. Results of the performance tests and the plant growth tests of the OW solar lighting system showed that the OW system is a viable plant lighting system for growing plant in space.

Ecological Systems, Closed↗
PubMedDate not supplied

An introduction to attenuation correction.

Attenuation correction techniques have demonstrated improved diagnostic accuracy and quality of myocardial perfusion SPECT images in limited studies. The future success of these methods relies largely on understanding the characteristics of the images and their interpretative meaning, as well as their limitations. It will be important to define the impact on patient management decisions, quantitation, laboratory efficiency physician confidence, and communication of important findings. Advances in these areas will help position nuclear cardiology to compete with other imaging modalities. As this technology matures, the technologist has an essential role in ensuring efficient use of these techniques and maximizing the quality of this promising new way to image patients.

Artifacts↗