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At least 127 records · Page 7Linked to original sources
PubMed1988

[Clinical usefulness of a dual photon absorptiometry system using X-ray for peripheral bone--comparison with a single photon absorptiometric system].

A newly developed dual photon absorptiometry system (DCS-600, ALOKA Co., LTD.) using two monochromatic X-rays for the determination of bone mineral in the peripheral bone was fundamentally studied, in comparison to single photon absorptiometry system (SPA). The accuracy and precision in DCS-600 were equal to or better than SPA system. Furthermore, in DCS-600 the forearm could be imaged, and the manipulation was easy. Thus DCS-600 was found to be a good instrument as a quantifying system of bone mass.

Bone and Bones↗
PubMed1984

Subtraction of Compton-scattered photons in single-photon emission computerized tomography.

A technique for scatter correction in single photon emission computerized tomography (SPECT) is described. The method is based on "deconvolution" of scattered events from the measured profile data. The function defining the scatter distribution was determined from measurements with a line source in circular and rectangular water phantoms. The accuracy of the method was tested on a simple phantom simulating a SPECT investigation of the liver. The indicated ratio of the activity concentration in a photon-deficient area, 60 mm diameter in the "liver", relative to its surroundings, was 0.28/1 without scatter correction and 0.01/1 with the correction.

Liver↗
PubMed1994

Analytic modeling of photon scatter from flattening filters in photon therapy beams.

Analytic models for calculation of scatter distributions from flattening filters in therapy photon beams are presented. It is shown that the amount of scatter with high atomic number filters can vary from 2% in 4-MV beams to 10% for 24-MV beams. The use of low atomic number filters can increase the amount of scatter by a factor of 2. The dependence on the opening angle of the primary collimator is quite large since a larger opening angle requires a thicker filter, which increases the scattered fraction of the filtered beam. The scatter makes the filter act as an extended source of extra-focal radiation. The source distribution for monomedia filters is shown to be almost triangular. Integration in the calculation-point's eye view over the visible part of the filter scatter source yields the scatter fraction of the total energy fluence incident upon the patient. The experimentally well-known "tilt" of dose profiles for asymmetrical fields is explained by the model. For complete modeling of head scatter distributions in treatment planning, the model presented must be combined with models also describing the scatter from the collimators, auxiliary modulators such as wedges and compensating filters, and collimator backscatter to the beam monitor.

Humans↗
PubMed1992

Paradoxical enhancement of hypoperfusion single photon emission CT images in epileptic focus with bemegride activation. Observation from subtraction of 99mTc hexamethyl-propyleneamine oxime brain single photon emission CT images.

Changes of brain images in single photon emission CTs (SPECTs) before and after intravenous injection of bemegride were examined with simultaneous EEG recording in a patient with occipital lobe epilepsy and in a hysteric patient, using a new method, i.e. subtraction of the SPECT images with 99mTc hexamethyl-propyleneamine oxime. The bemegride injection in the epileptic patient paradoxically intensified the hypoperfusion images as epileptic foci in SPECTs, associated with enhanced interictal epileptic discharges, whereas the hysteric showed no such effects. These findings suggest that the hypoperfusion images closely correlate to the severity of epileptic activity, reflecting a functional rather than a morphological deficit.

Adult↗
PubMed1999

[Assessment of left ventricular function by electrocardiogram-gated myocardial single photon emission computed tomography using quantitative gated single photon emission computed tomography software].

Electrocardiogram (ECG)-gated myocardial single photon emission computed tomography (SPECT) can assess left ventricular (LV) perfusion and function easily using quantitative gated SPECT (QGS) software. ECG-gated SPECT was performed in 44 patients with coronary artery disease under post-stress and resting conditions to assess the values of LV functional parameters, by comparison to LV ejection fraction derived from gated blood pool scan and myocardial characteristics. A good correlation was obtained between ejection fraction using QGS and that using cardiac blood pool scan (r = 0.812). Some patients with myocardial ischemia had lower ejection fraction under post-stress compared to resting conditions, indicating post-stress LV dysfunction. LV wall motion and wall thickening were significantly impaired in ischemic and infarcted myocardium, and the degree of abnormality in the infarcted areas was greater than in the ischemic area. LV functional parameters derived using QGS were useful to assess post-stress LV dysfunction and myocardial viability. In conclusion, ECG-gated myocardial SPECT permits simultaneous quantitative assessment of myocardial perfusion and function.

Electrocardiography↗
PubMed1991

Evaluation of high energy photon external beam treatment planning: project summary. Photon Treatment Planning Collaborative Working Group.

A three-year project for the "Evaluation of High Energy Photon External Beam Treatment Planning," sponsored by the National Cancer Institute, is summarized. The participants in this project were determined on a competitive basis and included staff from four institutions: Massachusetts General Hospital; Memorial Sloan-Kettering Cancer Center; the University of Pennsylvania; and Mallinckrodt Institute of Radiation. This project built on the developments in three-dimensional anatomical and dose distribution reconstruction at these institutions and on the clinical guidance at these centers for quantitative evaluation of treatment plans. Protocols for acceptance of patients with lesions at eight different sites were developed and utilized. The technical methodology for interchange of treatment planning tapes, specifications for computerized tomography sections and their reconstruction, and the employment of dose-volume histograms of target regions and specified normal tissues and organs were all developed. Data were accumulated for tumor control probabilities (TCP) and for normal tissue complication probabilities (NTCP) for use in treatment plan design and evaluation. Several treatment parameters were studied as influenced by the availability of three-dimensional treatment planning and specific conclusions were reached.

Humans↗
PubMed2006

Simultaneous two-photon excited fluorescence and one-photon excited phosphorescence from single molecules of an organometallic complex Ir(ppy)3.

We report a study of excited-state lifetimes of the phosphorescent organometallic complex Ir(ppy)3 on ensemble and a single-molecule level. With decreasing concentration, an increasingly intense fast component of 3 ns lifetime appears next to the 1.1 mus phosphorescence. Experimental evidence suggests that strong two-photon absorption followed by fluorescence is responsible for the fast lifetime component.

Journal Article↗
PubMed2005

Photonic band gap effects on spontaneous emission lifetimes of an assembly of atoms in two-dimensional photonic crystals.

The lifetime distribution functions of the spontaneous emission (SE) of the excited atoms embedded in two-dimensional (2D) photonic crystals (PCs) with square lattice, consisting of square air rods in dielectric medium with different filling factors, are calculated by using the plane wave expansion method. The numerical results show that the SE in the 2D PCs cannot be prohibited completely but it can be inhibited intensively by the pseudo-PBG of the PCs. In the pseudoband edges, the SE is accelerated obviously. The reduced average lifetime of the excited atoms and the extension of the reduced lifetime distribution in the 2D PCs both are the same as those in the 3D PCs in the order of magnitude. Our results provide an available way to control the behavior of the SE by changing the structures of the 2D PCs.

Journal Article↗
PubMedDate not supplied

Scattered photons as the cause for the observed dmax shift with field size in high-energy photon beams.

Measurements on the Sagittaire linear accelerator and Allis-Chalmers betatron at M. D. Anderson Hospital indicate that the observed dmax shift with field size is due to the presence of Compton-scattered photons in the therapy beam, and not electrons as proposed by others. Separating the primary from other radiation components indicates that the secondary fraction represents a percentage contribution to the overall beam that increases as the collimators are opened. This is consistent with what would be expected from Compton scattering and explains the effective softening of the beam as field size increases.

Radiotherapy Dosage↗
PubMed2006

Photon-number-resolving detection at a telecommunications wavelength with a charge-integration photon detector.

We demonstrate multiphoton discrimination at a telecommunications wavelength with the readout frequency of 40 Hz by a charge-integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a preamplifier in a charge-integration circuit, which is cooled to 4.2 K to reduce thermal noise. The quantum efficiency of the CIPD (the detector itself) is 80% for 1530 nm light, and the readout noise is measured as 0.26 electrons at 40 Hz. We can construct Poisson distributions of photocarrier numbers with distinct peaks at each photocarrier number, corresponding to a signal-to-noise ratio of about 3.

Journal Article↗
PubMed1991

State-of-the-art of external photon beam radiation treatment planning. Photon Treatment Planning Collaborative Working Group.

A virtual revolution in computer capability has occurred in the last few years, largely based on rapidly decreasing costs and increasing reliability of digital memory and mass-storage capability. These developments have now made it possible to consider the application of both computer and display technologies to a much broader range of problems in radiation therapy, including planning of treatment, dose computation, and treatment verification. Several methods of three-dimensional dose computations in heterogeneous media capable of 3% accuracy are likely to be available, but significant work still remains, particularly for high energy x-rays where electron transport, and possibly pair production, need to be considered. Innovative display and planning techniques, as well as plan evaluation schemes, are emerging and show great promise for the future. No doubt these advances will lead to substantially improved treatment planning systems in the next few years. However, it must be emphasized that for many of these applications a tremendous software and hardware development effort is required.

Computer Graphics↗