Abstract:
:We propose the use of conic and cubic surface equations (surfaces of second and third order) to directly approximate the dual-energy equations (the integral equations for the dual-energy log-signal functions, i.e., the negative logarithms of the relative detector signals, considered as functions of the basis-material component thicknesses of the object) and especially their inverses. These types of surface equations require a minimum number of calibration points, and their solutions are smooth, monotonic functions with the correct linear asymptotic behavior. The accuracy of this method is investigated and compared to that of conventional polynomial approximations, both for simulated and real calibration data, taken from two split-detector systems. These systems provide a more stringent test of our method than comparable dual-kVp systems, due to the greater nonlinearity of their log-signal and inverse functions. For these systems, we show that direct approximation of the inverse dual-energy equations using the simple eight-term rational form of the conic surface equation provides an extremely fast decomposition algorithm, which is accurate, robust in the presence of noise, and which can be calibrated with as few as 9 calibration points, or robustly calibrated, with a built-in accuracy check, using only 16 calibration points. Also, we show that extreme accuracy of approximation (to within less than 10(-6) in log-signal and 1 micron in material thickness) is theoretically attainable using the eighteen-term form of the cubic surface equation, which has a closed-form analytic solution. Finally, we consider the effects of noise on calibration accuracy, and derive simple formulas which relate the true and apparent root-mean-square (rms) accuracies. These formulas then allow the comparison of the true rms calibration accuracies of various surface approximations, considered as functions of the total calibration heat loading of the x-ray tube.
journal_name
Med Physjournal_title
Medical physicsauthors
Cardinal HN,Fenster Adoi
10.1118/1.596512subject
Has Abstractpub_date
1990-05-01 00:00:00pages
327-41issue
3eissn
0094-2405issn
2473-4209journal_volume
17pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:The spatial resolution of iterative reconstruction (IR) in computed tomography (CT) is contrast- and noise-dependent because of the nonlinear regularization. Due to the severe noise contamination, it is challenging to perform precise spatial-resolution measurements at very low-contrast levels. The purpose of th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4916802
更新日期:2015-05-01 00:00:00
abstract:PURPOSE:To characterize a new air vented ionization chamber technology, suitable to build detector arrays with small pixel pitch and independence of sensitivity on dose per pulse. METHODS:The prototype under test is a linear array of air vented ionization chambers, consisting of 80 pixels with 3.5 mm pixel pitch dista...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4945414
更新日期:2016-05-01 00:00:00
abstract:PURPOSE:Lung cancer is a major cause of cancer deaths, and the 5-year survival rate of stage IV lung cancer patients is only 2%. However, the 5-year survival rate of stage I lung cancer patients significantly increases to 50%. As such, spiral computed tomography (CT) scans are necessary to diagnose high-risk lung cance...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12331
更新日期:2017-08-01 00:00:00
abstract:PURPOSE:MR-guided radiation therapy (RT) offers unparalleled soft tissue contrast for localization and target tracking. However, MRI distortions may be detrimental to high precision RT. This work characterizes the gradient nonlinearity (GNL) and total distortions over the first year of clinical operation of a 0.35T MR-...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13467
更新日期:2019-05-01 00:00:00
abstract:PURPOSE:Ultrasound-induced mild hyperthermia has advantages for noninvasive, localized and controlled drug delivery. In this study, a tissue-mimicking agarose-based phantom with a thermally sensitive indicator was developed for studying the spatial drug delivery profile using ultrasound-induced mild hyperthermia. METH...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4813299
更新日期:2013-08-01 00:00:00
abstract:PURPOSE:To investigate tight-frame based iterative reconstruction (TFIR) technique for spectral breast computed tomography (CT) using fewer projections while achieving greater image quality. METHODS:The experimental data were acquired with a fan-beam breast CT system based on a cadmium zinc telluride photon-counting d...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4790468
更新日期:2013-03-01 00:00:00
abstract:PURPOSE:Several works have recently focused on flattening-filter-free (FFF) beams of linear accelerators of various companies (in particular, Varian and Elekta), but no overview as yet exists for the flattening-filter free 7XU beam (Siemens Artiste). METHODS:Dosimetric properties of the 7XU beam were measured in May a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3703835
更新日期:2012-05-01 00:00:00
abstract:PURPOSE:The implementation of an accurate beam model is an integral part of the commissioning of any planning system. This process is especially challenging in the case of IMRT beam models owing to the complexity of small field sizes and MLC leaf-end and tongue-and-groove effects. The question of how to judge the quali...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735679
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:The authors investigate the impact that incremental increases in the level of detail of patient-specific prior information have on image quality and the convergence behavior of an inversion algorithm in the context of near-field microwave breast imaging. A methodology is presented that uses image quality measur...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12585
更新日期:2017-12-01 00:00:00
abstract::Single-photon emission-computed tomography (SPECT) imaging of deep brain structures is compromised by loss of photons due to attenuation. We have previously shown that a centrally peaked collimator sensitivity function can compensate for this phenomenon, increasing sensitivity over most of the brain. For dual-head ins...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1929208
更新日期:2005-07-01 00:00:00
abstract:PURPOSE:To demonstrate, via Monte Carlo simulation, that an image obtained from the patient-generated scattered radiation forced to impinge on the detector from a known direction by means of parallel-focused grids, can be used to complement the information conveyed by the primary image, such that accurate stereoscopic ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12712
更新日期:2018-02-01 00:00:00
abstract:PURPOSE:To describe and mathematically validate the superiorization methodology, which is a recently developed heuristic approach to optimization, and to discuss its applicability to medical physics problem formulations that specify the desired solution (of physically given or otherwise obtained constraints) by an opti...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4745566
更新日期:2012-09-01 00:00:00
abstract:PURPOSE:Quantitative cone-beam CT (CBCT) imaging is on increasing demand for high-performance image guided radiation therapy (IGRT). However, the current CBCT has poor image qualities mainly due to scatter contamination. Its current clinical application is therefore limited to patient setup based on only bony structure...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3693050
更新日期:2012-04-01 00:00:00
abstract::We present a theoretical development and experimental verification of a description of power loss and sample resistance for a lossy sample in a nuclear magnetic resonance radio frequency coil for a sample geometry where the eddy current streamlines are disrupted from their usually assumed circular paths. Specifically ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596336
更新日期:1989-09-01 00:00:00
abstract::A commercially available open MRI unit is under routine use for radiation therapy simulation. The effects of a gradient distortion correction (GDC) program used to post process the images were assessed by comparison with the known geometry of a phantom. The GDC reduced the magnitude of the distortions at the periphery...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1513991
更新日期:2002-11-01 00:00:00
abstract::Flat-panel imagers consisting of the first large area, self-scanning, pixelated, solid-state arrays made with hydrogenated amorphous silicon (a-Si:H) are under development by the authors for applications in diagnostic x-ray and megavoltage radiotherapy imaging. The arrays, designated by the acronym MASDA for multi-ele...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596802
更新日期:1992-11-01 00:00:00
abstract::Two side-by-side energy windows are sometimes employed in quantitative single photon emission computed tomography (SPECT) studies. The count-rate losses at high activities for a GE400AT camera were measured in such a dual-window-acquisition mode by imaging a decaying source composed of a hot sphere within a warm cylin...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597008
更新日期:1993-07-01 00:00:00
abstract::The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity-modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpos...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2737158
更新日期:2007-06-01 00:00:00
abstract:PURPOSE:Periprocedural assessment of tissue perfusion by imaging methods could improve outcome control during treatment of peripheral vascular disease. Currently, endovascular revascularization treatments are assessed by planar angiography which only allows for qualitative inspection of blood flow in vessels. In this p...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3679864
更新日期:2012-03-01 00:00:00
abstract:PURPOSE:To investigate how using different sets of decision criteria impacts the quality of intensity modulated radiation therapy (IMRT) plans obtained by multiobjective optimization. METHODS:A multiobjective optimization evolutionary algorithm (MOEA) was used to produce sets of IMRT plans. The MOEA consisted of two i...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3589128
更新日期:2011-06-01 00:00:00
abstract::Administration of x-ray contrast agents during heart catheterization examination increases the absorbed radiation dose in tissue. To estimate the dose absorbed by the blood of children undergoing diagnostic heart catheterization and angiocardiography, a number of measurements and calculations were conducted. First, en...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594613
更新日期:1979-11-01 00:00:00
abstract:PURPOSE:Diabetic retinopathy (DR) is one of the most widespread causes of preventable blindness in the world. The most dangerous stage of this condition is proliferative DR (PDR), in which the risk of vision loss is high and treatments are less effective. Fractal features of the retinal vasculature have been previously...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12627
更新日期:2017-12-01 00:00:00
abstract:PURPOSE:Stereotactic ablative body radiotherapy (SABR) for lung patients can be performed with volumetric-modulated arc therapy (VMAT) plans using off-axis target geometry to allow treatment in their CBCT verified position. For patient-specific quality assurance measurements using the PTW Octavius 4D phantom (PTW, Frei...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12805
更新日期:2018-04-01 00:00:00
abstract:PURPOSE:To evaluate if the recently described problems with the calibration of jaws at Varian linear accelerators can be detected with the DAVID system. METHODS:Recently Varian Clinac field size issues resulted in a widespread medical device correction notice, stating that incorrect jaw positioning due to excessive co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4736189
更新日期:2012-06-01 00:00:00
abstract::It is well-known that the edge effect produced by phase contrast imaging results in the edge enhancement of x-ray images and thereby sharpens those images. It has recently been reported that phase contrast imaging using practical x-ray tubes with small focal spots has improved image sharpness as observed in the phase ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1992087
更新日期:2005-08-01 00:00:00
abstract:PURPOSE:Dedicated breast PET/CT is expected to have utility in local staging, surgical planning, monitoring of therapy response, and detection of residual disease for breast cancer. Quantitative metrics will be integral to several such applications. The authors present a validation of fully 3D data correction schemes f...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3703593
更新日期:2012-05-01 00:00:00
abstract::Reconstruction of electron spectra of medical accelerators from measured depth dose distributions is an attractive tool for commissioning of a Monte Carlo treatment planning system. However, the reconstruction method is an inverse radiation transport problem which is poorly conditioned, in the sense it may become unst...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1461840
更新日期:2002-04-01 00:00:00
abstract::The Gafchromic EBT was recently introduced in film dosimetry for external beam therapy (EBT). The high spatial resolution, weak energy dependence, and near-tissue equivalence of EBT films make them suitable for measurement of dose distributions in radiotherapy, especially intensity-modulated radiation therapy (IMRT). ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2362876
更新日期:2006-11-01 00:00:00
abstract:PURPOSE:Manual delineation of head and neck (H&N) organ-at-risk (OAR) structures for radiation therapy planning is time consuming and highly variable. Therefore, we developed a dynamic multiatlas selection-based approach for fast and reproducible segmentation. METHODS:Our approach dynamically selects and weights the a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13854
更新日期:2019-12-01 00:00:00
abstract::The main purpose of this work is to demonstrate a practical means of determining the leaf transmission and scatter characteristics of a multileaf collimator (MLC) pertinent to the commissioning of dynamic intensity modulated radiotherapy, especially for the sweeping window technique. The data are necessary for the con...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1312190
更新日期:2000-10-01 00:00:00