Abstract:
:Cone beam transmission CT (CB-CT) improves SPECT imaging by providing high-quality attenuation maps for attenuation compensation and for correlated SPECT and CT imaging. The present work measures the detection nonuniformity for CB-CT implemented with a gamma camera, and applies nonuniformity corrections to make CB-CT more uniform and accurate. Two cone beam collimators were investigated, as well as the uncollimated cone beam geometry, using both uniformity images and CB-CT reconstructions of a uniform circular cylinder. Uniformity images were acquired as a function of point source position relative to the nominal focal point. The uniformity images for both collimators were highly nonuniform, with some regions differing by more than 15% from the average image counts per pixel, indicating that the holes do not focus to the same point. The most uniform images were obtained with the point source located at or near the nominal focal point. Radiographs estimated the misfocusing of the holes to be about 0.6 degrees in some regions. There were no indications that the hole size was nonuniform. The CB-CT reconstructions of data acquired with collimator showed no obvious signs of image artifact from the detection nonuniformities. However, low-noise simulated data with well-localized detection defects produced readily-apparent circular artifacts. The nonuniformity correction was accurate and easy to apply, and should be used whenever quantitative accuracy is required. The uniformity images acquired without collimator lacked the collimator-produced nonuniformities, but had decreased counts near the detector edge. The decrease was predictable, using simple geometric considerations. Uniform cylinder reconstructions of "without collimator" data showed a corresponding decrease in center density relative to the edge (edge-to-center ratio = 1.25), which was improved by the nonuniformity correction (ratio = 0.21). Accurate CB-CT without collimator will require further correction for photon scatter.
journal_name
Med Physjournal_title
Medical physicsauthors
Manglos SH,Capone RB,Bassano DAdoi
10.1118/1.596838subject
Has Abstractpub_date
1992-03-01 00:00:00pages
491-500issue
2eissn
0094-2405issn
2473-4209journal_volume
19pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:Patient-specific QA of highly conformal radiotherapy treatments are usually conducted using 2D or 3D dosimetry of the incident dose distribution in a water-equivalent phantom. However, dosimeters typically used for this task usually lack in either spatial resolution or dose accuracy. The purpose of this work is...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4736526
更新日期:2012-08-01 00:00:00
abstract:PURPOSE:We have developed a robust tool for performing volumetric and temporal analysis of nodules from respiratory gated four-dimensional (4D) CT. The method could prove useful in IMRT of lung cancer. METHODS:We modified the conventional graph-cuts method by adding an adaptive shape prior as well as motion informatio...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12690
更新日期:2018-01-01 00:00:00
abstract:PURPOSE:To measure patient-specific maximum skin dose (MSD) associated with CT fluoroscopy (CTF) lung biopsies and to compare measured MSD with the MSD estimated from phantom measurements, as well as with the CTDIvol of patient examinations. METHODS:Data from 50 patients with lung lesions who underwent a CT fluoroscop...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4884231
更新日期:2014-07-01 00:00:00
abstract::Multi-instrument activity estimation and decay correction techniques were developed for radionuclide mixtures, motivated by the desire for accurate quantitation of Tc-94m positron emission tomography (PET) studies. Tc-94m and byproduct Tc isotopes were produced by proton irradiation of enriched Mo-94 and natural Mo ta...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1333411
更新日期:2001-01-01 00:00:00
abstract:PURPOSE:To investigate the optimal use of XR-RV3 GafChromic(®) films to assess patient skin dose in interventional radiology while addressing the means to reduce uncertainties in dose assessment. METHODS:XR-Type R GafChromic films have been shown to represent the most efficient and suitable solution to determine patie...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4922132
更新日期:2015-07-01 00:00:00
abstract::This study proposes an algorithm for selecting beam weight, wedge angle, and wedge orientation for three-dimensional radiation therapy treatment planning. According to dose gradient analysis, the necessary and sufficient condition for achieving a homogeneous dose over the target volume is that the total vector sum of ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1286591
更新日期:2000-08-01 00:00:00
abstract::This paper examines the distributions of the SAR (specific absorption rate) ratio and temperature elevation when an ultrasound beam propagates through the interface of muscle and bone. This interface is regarded as a flat boundary to partition the energy of the ultrasound beam, and the analytical solution of temperatu...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598979
更新日期:2000-05-01 00:00:00
abstract:PURPOSE:For the purpose of size-specific dose estimation, information regarding patient attenuation is required. The purpose of this work is to describe a method for measuring patient attenuation and expressing the results in terms of a water cylinder, with cross sectional area A(w), which would absorb the same average...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4754303
更新日期:2012-11-01 00:00:00
abstract::The purpose of this work is to show the feasibility of using in vivo proton radiography of a radiotherapy patient for the patient individual optimization of the calibration from CT-Hounsfield units to relative proton stopping power. Water equivalent tissue (WET) calibrated proton radiographs of a dog patient treated f...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1833041
更新日期:2005-01-01 00:00:00
abstract:PURPOSE:To characterize the radiation dose and three-dimensional (3D) imaging performance of a recently developed mobile, isocentric C-arm equipped with a flat-panel detector (FPD) for intraoperative cone-beam computed tomography (CBCT) (Cios Spin 3D, Siemens Healthineers) and to identify potential improvements in 3D i...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13983
更新日期:2020-03-01 00:00:00
abstract:PURPOSE:To accurately and efficiently implement charged particle transport in a magnetic field in EGSnrc and validate the code for the use in phantom and ion chamber simulations. METHODS:The effect of the magnetic field on the particle motion and position is determined using one- and three-point numerical integrations...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4954318
更新日期:2016-07-01 00:00:00
abstract:PURPOSE:The purpose of this study is to evaluate the feasibility of kilovoltage cone-beam CT (CBCT) images that are obtained with the Varian On-Board Imager in dose calculation at each radiation therapy. METHODS:CBCT images are commonly degraded by scattered radiations originating in the patient's body, and so the CT ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734936
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Mammography is known to be one of the most difficult radiographic exams to interpret. Mammography has important limitations, including the superposition of normal tissue that can obscure a mass, chance alignment of normal tissue to mimic a true lesion and the inability to derive volumetric information. It has b...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3562901
更新日期:2011-04-01 00:00:00
abstract:PURPOSE:The determination of absorbed dose to water from external beam radiotherapy using radiation detectors is currently rooted in calibration protocols that do not account for modulations encountered in patient-specific deliveries. Detector response in composite clinical fields has not been extensively studied due t...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13293
更新日期:2019-02-01 00:00:00
abstract::Image intensifier-television-video digitizer (IITVD) systems are commonly used for digital planar image acquisition in radiology. However, the well-known distortions inherent in these systems limit their utility in research and in some clinical applications where quantitatively correct images are required. Software co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596718
更新日期:1991-03-01 00:00:00
abstract::A computer program was implemented to predict mammography x-ray beam parameters in the range 20-40 kV for Mo/Mo, Mo/Rh, Rh/Rh, and W/Al target/filter combinations. The computation method used to simulate mammography x-ray spectra is based on the Boone et al. model. The beam quality parameters such as the half-value la...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1608498
更新日期:2003-10-01 00:00:00
abstract:PURPOSE:Arterial distensibility is a marker that can measure vessel wall functional and structural changes resulting from atherosclerosis with applications including estimation of mechanical properties of the wall. We sought to assess the feasibility of using magnetic resonance imaging (MRI) to include wall distensibil...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4754302
更新日期:2012-10-01 00:00:00
abstract::Functional single photon emission computed tomography (SPECT) images of brain activation are based on a comparison of base line and activation images. The correctness of the functional images depends, among other factors, on the accurate spatial registration (alignment) of the base line and activation image data. The ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597228
更新日期:1994-12-01 00:00:00
abstract:PURPOSE:To evaluate the performance and efficacy for intensity inhomogeneity correction of various sequences of the human brain in 7T MRI using the extended version of the unified segmentation algorithm. MATERIALS:Ten healthy volunteers were scanned with four different sequences (2D spin echo [SE], 3D fast SE, 2D fast...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4860954
更新日期:2014-02-01 00:00:00
abstract:PURPOSE:To Validate Brainlab-ExacTrac IGRT with Dot-Decimal electron compensator(BolusECT) for accurate patient positioning. METHODS:Dot-Decimal electron compensators(BolusECT) are used to achieve conformal dose distributions and greater sparing to normal structures for cases with varying patient contours and treated ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734881
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:To increase diagnostic accuracy of breast MRI by increasing temporal resolution and more accurately sampling the early kinetics of contrast media uptake. We tested the feasibility of accelerating bilateral breast DCE-MRI by reducing the FOV, allowing aliasing, and unfolding the resulting images. METHODS:Previo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12747
更新日期:2018-03-01 00:00:00
abstract::Quantitative evaluation of cardiac image data obtained using multidetector row computed tomography (CT) is compromised by partial scan reconstructions, which improve the temporal resolution but significantly increase image-to-image CT number variations for a fixed region of interest compared to full reconstruction ima...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2805476
更新日期:2007-12-01 00:00:00
abstract:PURPOSE:Modern CT systems adjust X-ray flux accommodating for patient size to achieve certain image noise values. The effectiveness of this adaptation is an important aspect of CT performance and should ideally be characterized in the context of real patient cases. The objective of this study was to characterize CT per...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12172
更新日期:2017-06-01 00:00:00
abstract::We describe a unique method that allows the comparison of spatially registered ultrasound (SRUS) images and computed tomography-derived contours (CTDCs) that were acquired with a minimal time lapse. As such, we have a tool that will provide validation of the spatial accuracy of the US system and that will allow compar...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1644515
更新日期:2004-03-01 00:00:00
abstract:PURPOSE:The purpose of this study was to investigate the potential of MR-guided pulsed focused ultrasound (pFUS) for the enhancement of drug uptake in prostate tumors in vivo using doxorubicin (Dox). METHODS:An antitumor drug Dox, an orthotopic animal prostate tumor model using human prostate cancer, LNCaP cell line, ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4705346
更新日期:2012-05-01 00:00:00
abstract:PURPOSE:Water equivalent diameter (WED) is the preferred surrogate for patient size in CT. It is better than geometric size surrogates and patient weight/height/BMI/age because it correlates the best with x-ray attenuation. The administration of oral/IV contrast agents increases a patient's attenuation and should there...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14721
更新日期:2021-01-13 00:00:00
abstract:PURPOSE:To obtain on-treatment volumetric patient anatomy during respiratory gated volumetric modulated arc therapy (VMAT). METHODS:On-board imaging device integrated with Linacs offers a viable tool for obtaining patient anatomy during radiation treatment delivery. In this study, the authors acquired beam-level kV im...
journal_title:Medical physics
pub_type: 信件
doi:10.1118/1.4794925
更新日期:2013-04-01 00:00:00
abstract::When parallel-plate chambers are used for dosimetry in electron fields, the AAPM dosimetry protocol recommends a value of 1.0 for the replacement correction factor, P(repl),pp,E, until further data become available. Here, P(repl),pp,E for five commercially available parallel-plate chambers was measured as a function o...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596740
更新日期:1991-11-01 00:00:00
abstract:PURPOSE:The thermoluminescence dosimeter (TLD) has desirable features including low cost, reusability, small size, and relatively low energy dependence. However, the commonly available poly-crystal TLDs (e.g., TLD-100) exhibit high interdetector variability that requires individual calibration for high detection accura...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13895
更新日期:2020-01-01 00:00:00
abstract:PURPOSE:IAEA TRS-398 notes that cylindrical ionization chambers are preferred for reference proton dosimetry. If a cylindrical ionization chamber is used in a phantom to measure the dose as a function of depth, the effective point of measurement (EPOM) must be taken into account. IAEA TRS-398 recommends a displacement ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4921617
更新日期:2015-07-01 00:00:00