摘要:

In this work the fast-simulated annealing method has been applied to the design of a gradient coil set for head imaging. This stochastic approach is based on the optimization of a parametrized stream function and allows the design of very short self-shielded gradient coils. The main advantage of this technique is its ability to enlarge the homogeneous gradient volume produced by short gradient coils. As a result of the optimization process, low-inductance coils producing large homogeneous gradient volumes with high gradient efficiency were obtained. The optima sets of parameters are given to simplify the construction of gradient coils for head imaging. The quality of these coils is studied by considering efficiency, inductance, and homogeneity of the gradient field, and an analysis of the magnetic force applied on the coils is presented. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420461

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

In this paper it is described some to those characteristics of silicon detectors which make them very useful in the fields of Medical Physics. The main application of these devices are in detecting low energy X-ray radiation (from 10 to 100 KeV). This range of energy is enough in many applications on crystallographic and on medical imaging. This paper also briefly refers to the readout system for acquiring the radiation events for imaging purposes. Finally, it is discussed the different kinds of silicon detectors which are silicon strip, pixel and drift. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420462

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Ionizing radiation can create stable free radicals in solids that can be quantified, in a nondestructive way, by Electron Spin Resonance (ESR) leading to a dosimetric technique. Ionizing radiation can change the valence of iron ions and the viscosity of certain polymers leading to changes in the relaxation times of protons, allowing the use o nuclear magnetic resonance imaging (MRI) to image three-dimensional dose distribution. Both techniques are expected to improve the quality of medical care that rely on the use of ionizing radiation. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420463

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

In this work Monte Carlo calculations and experimental measurements of dose rate in water per unit air-kerma strength,D˙/Sk,of a low dose rate Amersham CDCS.J137Cssource are reported. The Monte Carlo calculations included a detailed simulation of the geometric structure of the source embedded in a water medium. The experimental procedure included the construction of a lucite phantom with the same geometric characteristics as the one used in the simulation. Dose measurements were performed using high spatial resolution RadioChromic dye film and TL dosemeters for short and large distances from the source, respectively. The comparison between simulated and reported values in the literature ofD˙/Skfor the same source are of 1.0&percent; in average [1]. The differences between the TL measurements and the simulation also are of 1&percent; in average, while the difference between the MC and the RadioChromic film are larger, particularly when the RadioChromic film received doses smaller than 7 Gy. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420464

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Medical physics research is providing new avenues for addressing the fundamental problem of radiation therapy-how to provide a tumor-killing dose while reducing the dose to a non-lethal level for critical organs in adjacent portions of the patient anatomy. This talk reviews the revolutionary impact of Positron Emission Tomography on the practice of radiation oncology. The concepts of PET imaging and the development of “tumor” imaging methods using18F-DGflouro-deoxyglucose are presented to provide the foundation for contemporary research and application to therapy. PET imaging influences radiation therapy decisions in multiple ways. Imaging of occult but viable tumor metastases eliminates misguided therapy attempts. The ability to distinguish viable tumor from scar tissue and necroses allows reduction of treatment portals and more selective treatments. Much research remains before the clinical benefits of these advances are fully realized. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420465

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Deuterium(2H)microscopic images with resolution of tens of microns and localized2Hspectra with volumes in the micro liter range have been obtained on a Varian 400 MHz (9.4T) wide bore spectrometer equipped with a 50 G/cm gradient system. In order to realize2Hexperiments at 61.4 MHz, a simple RF coil was built.2H-Microimaging experiments have been carried out with SE and FLASH pulse sequences and localized2H-spectroscopy has been tested on a phantom, which consists of a2×2×2 mm3cube withCD3ODimmersed inD2O.Results show that non-invasive investigation of biological samples is possible. As an example for a biological application, the absorption process ofD2Oin a plant fragment (Mikania Cordifolia) has been monitored by acquiring consecutive SE microimages along various hours. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420466

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Conventional or external beam radiotherapy, has been a viable alternative for cancer treatment. Although this technique is effective, its use is limited if the patient has multiple malignant lesions (metastases). An alternative approach is based on the design of radiopharmaceuticals that, to be administered in the patient, are directed specifically toward the target cell producing a selective radiation delivery. This treatment is known as targeted radiotherapy. We have summarized and discussed some results related to our investigations on the development of targeted radiotherapy systems, including aspects of internal dosimetry. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420467

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Under the auspices of PAHO/WHO, a multicentric investigation is carried out in five Latin American countries. Its aim is to correlate quality indicators of radiology services with the accuracy of the radiological interpretation as determined by a panel of radiology experts. We present preliminary results from mammographic imaging facilities. Evaluation of the equipment performance and dose measurements in 21 mammographic units show that, on the average, 75&percent; of the units comply with recommendations issued by various organizations. An independent evaluation of the quality of the clinical images show strong variations among the different radiological services. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420468

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Central nervous system studies of injury and plasticity for the reorganization in the phantom limb sensation area presented. In particular functional magnetic resonance imaging (fMRI) mapping of the somatic and motor cortex of amputee patients, in the case of referred sensations. Using fMRI we can show the correlation between structure and functional field and study the reorganization due to plasticity in the brain. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420469

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

MR imaging has experienced an important growth worldwide and in particular in the USA and Japan. This imaging technique has also shown an important rise in the number of MR imagers in Mexico. However, the development of MRI has followed a typical way of Latin American countries, which is very different from the path shown in the industrialised countries. Despite the fact that Mexico was one the very first countries to install and operate MR imagers in the world, it still lacks of qualified clinical and technical personnel. Since the first MR scanner started to operate, the number of units has grown at a moderate space that now sums up approximately 60 system installed nationwide. Nevertheless, there are no official records of the number of MR units operating, physicians and technicians involved in this imaging modality. The MRI market is dominated by two important companies: General Electric (approximately 51&percent;) and Siemens (approximately 17.5&percent;), the rest is shared by other five companies. According to the field intensity, medium-field systems (0.5 Tesla) represent 60&percent; while a further 35&percent; are 1.0 T or higher. Almost all of these units are in private hospitals and clinics: there is no high-field MR imagers in any public hospital. Because the political changes in the country, a new public plan for health care is still in the process and will be published soon this year. This plan will be determined by the new Congress. North American Free Trade Agreement (NAFTA) and president Fox. Experience acquired in the past shows that the demand for qualified professionals will grow in the new future. Therefore, systematic training of clinical and technical professionals will be in high demand to meet the needs of this technique. The National University (UNAM) and the Metropolitan University (UAM-Iztapalapa) are collaborating with diverse clinical groups in private facilities to create a systematic training program and carry out research and development in MRI ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1420470

出版商:AIP    

年代:1901

数据来源: AIP