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A model of mechanical interactions between heart and lungs.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
To study the mechanical interactions between heart, lungs and thorax, we propose a mathematical model combining a ventilatory neuromuscular model and a model of the cardiovascular system, as described by Smith et al. (Smith, Chase, Nokes, Shaw & Wake 2004 Med. Eng. Phys.26, 131-139. (doi:10.1016/j.medengphy.2003.10.001)). The respiratory model has been adapted from Thibault et al. (Thibault, Heyer, Benchetrit & Baconnier 2002 Acta Biotheor. 50, 269-279. (doi:10.1023/A:1022616701863)); using a Liénard oscillator, it allows the activity of the respiratory centres, the respiratory muscles and rib cage interna...
Source: Medical Physics - November 5, 2009 Category: Physics Authors: Fontecave Jallon J, Abdulhay E, Calabrese P, Baconnier P, Gumery PY Tags: Philos Transact A Math Phys Eng Sci Source Type: journals

Medial tibial stress syndrome: conservative treatment options.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Medial tibial stress syndrome (MTSS), commonly known as "shin splints," is a frequent injury of the lower extremity and one of the most common causes of exertional leg pain in athletes (Willems T, Med Sci Sports Exerc 39(2):330-339, 2007; Korkola M, Amendola A, Phys Sportsmed 29(6):35-50, 2001; Hreljac A, Med Sci Sports Exerc 36(5):845-849, 2004). Although often not serious, it can be quite disabling and progress to more serious complications if not treated properly. Often, the cause of MTSS is multi-factorial and involves training errors and various biomechanical abnormalities. Few advances have been made in the treat...
Source: Medical Physics - October 6, 2009 Category: Physics Authors: Galbraith RM, Lavallee ME Tags: Curr Rev Musculoskelet Med Source Type: journals

SpekCalc: a program to calculate photon spectra from tungsten anode x-ray tubes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A software program, SpekCalc, is presented for the calculation of x-ray spectra from tungsten anode x-ray tubes. SpekCalc was designed primarily for use in a medical physics context, for both research and education purposes, but may also be of interest to those working with x-ray tubes in industry. Noteworthy is the particularly wide range of tube potentials (40-300 kVp) and anode angles (recommended: 6-30 degrees ) that can be modelled: the program is therefore potentially of use to those working in superficial/orthovoltage radiotherapy, as well as diagnostic radiology. The utility is free to download and is based on ...
Source: Medical Physics - August 31, 2009 Category: Physics Authors: Poludniowski G, Landry G, Deblois F, Evans PM, Verhaegen F Tags: Phys Med Biol Source Type: journals

Construction of anthropomorphic phantoms for use in dosimetry studies.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper reports on the methodology and materials used to construct anthropomorphic phantoms for use in dosimetry studies, improving on methods and materials previously described by Jones et al. [Med Phys. 2006;33(9):3274-82]. To date, the methodology described has been successfully used to create a series of three different adult phantoms at the University of Florida (UF). All phantoms were constructed in 5 mm transverse slices using materials designed to mimic human tissue at diagnostic photon energies: soft tissue-equivalent substitute (STES), lung tissue-equivalent substitute (LTES), and bone tissue-equivalent su...
Source: Medical Physics - August 21, 2009 Category: Physics Authors: Winslow JF, Hyer DE, Fisher RF, Tien CJ, Hintenlang DE Tags: J Appl Clin Med Phys Source Type: journals

Point/counterpoint. Bright young physicists should be advised to avoid careers in radiation therapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19673183 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Schulz RJ, Podgorsak MB, Orton CG Tags: Med Phys Source Type: journals

A novel flexible framework with automatic feature correspondence optimization for nonrigid registration in radiotherapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article describes the design, the implementation, and the validation of a new framework for nonrigid registration for radiotherapy applications. The core of this framework is an improved version of the thin plate spline robust point matching (TPS-RPM) algorithm. The TPS-RPM algorithm estimates a global correspondence and a transformation between the points that represent organs of interest belonging to two image sets. However, the algorithm does not allow for the inclusion of prior knowledge on the correspondence of subset of points, and therefore, it can lead to inconsistent anatomical solutions. In this article TPS-...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Vásquez Osorio EM, Hoogeman MS, Bondar L, Levendag PC, Heijmen BJ Tags: Med Phys Source Type: journals

Multidivergent-beam stationary cardiac SPECT.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article develops a stationary cardiac single photon emission computed tomography (SPECT) system using a novel multidivergent-beam collimator. This stationary SPECT system is inexpensive to build, small, and able to acquire true dynamic SPECT data. Stationary cardiac SPECT systems with multipinhole technology already exist. The proposed approach is to replace the multipinhole collimators with the originally designed multidivergent-beam collimators. The motivation for replacing the pinhole technology by divergent-beam technology is based on the following facts. The resolution/sensitivity trade-off for the pinhole is exc...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Zeng GL, Stevens AM Tags: Med Phys Source Type: journals

Fractionated stereotactic radiotherapy: a method to evaluate geometric and dosimetric uncertainties using radiochromic films.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In the authors' hospital, stereotactic radiotherapy treatments are performed with a Varian Clinac 600C equipped with a BrainLAB m3 micro-multileaf-collimator generally using the dynamic conformal arc technique. Patient immobilization during the treatment is achieved with a fixation mask supplied by BrainLAB, made with two reinforced thermoplastic sheets fitting the patient's head. With this work the authors propose a method to evaluate treatment geometric accuracy and, consequently, to determine the amount of the margin to keep in the CTV-PTV expansion during the treatment planning. The reproducibility of the isocenter...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Coscia G, Vaccara E, Corvisiero R, Cavazzani P, Ruggieri FG, Taccini G Tags: Med Phys Source Type: journals

Dosimetric effects of rotational output variation and x-ray target degradation on helical tomotherapy plans.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, two potential sources of IMRT delivery error have been identified for helical tomotherapy delivery using the HiART system (TomoTherapy, Inc., Madison, WI): Rotational output variation and target degradation. The HiArt system is known to have output variation, typically about +/- 2%, due to the absence of a dose servo system. On the HiArt system, x-ray target replacement is required approximately every 10-12 months due to target degradation. Near the end of target life, the target thins and causes a decrease in the beam energy and a softening of the beam profile at the lateral edges of the beam. The purpose o...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Staton RJ, Langen KM, Kupelian PA, Meeks SL Tags: Med Phys Source Type: journals

Field-size effect of physical doses in carbon-ion scanning using range shifter plates.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A field-size effect of physical doses was studied in scanning irradiation with carbon ions. For the target volumes of 60 x 60 x 80, 40 x 40 x 80, and 20 x 20 x 80 mm3, the doses along the beam axis within the spread-out Bragg peaks reduced to 99.4%, 98.2%, and 96.0% of the dose for the target of 80 x 80 x 80 mm3, respectively. The present study revealed that the observed reductions can be compensated for by adopting the three-Gaussian form of lateral dose distributions for the pencil beam model used in the treatment planning system. The parameters describing the form were determined through the irradiation experiments ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Inaniwa T, Furukawa T, Nagano A, Sato S, Saotome N, Noda K, Kanai T Tags: Med Phys Source Type: journals

An exposure indicator for digital radiography: AAPM Task Group 116 (executive summary).Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Digital radiographic imaging systems, such as those using photostimulable storage phosphor, amorphous selenium, amorphous silicon, CCD, and MOSFET technology, can produce adequate image quality over a much broader range of exposure levels than that of screen/film imaging systems. In screen/film imaging, the final image brightness and contrast are indicative of over- and underexposure. In digital imaging, brightness and contrast are often determined entirely by digital postprocessing of the acquired image data. Overexposure and underexposures are not readily recognizable. As a result, patient dose has a tendency to grad...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Shepard SJ, Wang J, Flynn M, Gingold E, Goldman L, Krugh K, Leong DL, Mah E, Ogden K, Peck D, Samei E, Wang J, Willis CE Tags: Med Phys Source Type: journals

Skeletal dosimetry in cone beam computed tomography.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, voxelized human phantoms, FAX06 (adult female) and MAX06 (adult male), are used together with phase-space data collected from a realistic model of a CBCT imager to calculate dose in the red bone marrow (RBM) and bone surface cells (BSCs), the two organs at risk within the bone spongiosa, during simulated head and neck, chest and pelvis CBCT scans. The FAX06/MAX06 phantoms model spongiosa based on micro-CT images, filling the relevant phantom voxels, which are 0.12 x 0.12 x 0.12 cm3, with 17 x 17 x 17 microm3 microvoxels to form a micromatrix of trabecular bone and bone marrow. FAX06/ MAX06 have already been ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Walters BR, Ding GX, Kramer R, Kawrakow I Tags: Med Phys Source Type: journals

Pharmacokinetic analysis of tissue microcirculation using nested models: multimodel inference and parameter identifiability.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this study is to evaluate the identifiability of physiological tissue parameters by pharmacokinetic modeling of concentration-time curves derived under conditions that are realistic for dynamic-contrast-enhanced (DCE) imaging and to assess the information-theoretic approach of multimodel inference using nested models. Tissue curves with a realistic noise level were simulated by means of an axially distributed multipath reference model using typical values reported in literature on plasma flow, permeability-surface area product, and volume fractions of the intravascular and interstitial space. The simulat...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Brix G, Zwick S, Kiessling F, Griebel J Tags: Med Phys Source Type: journals

Automatic lung segmentation from thoracic computed tomography scans using a hybrid approach with error detection.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Lung segmentation is a prerequisite for automated analysis of chest CT scans. Conventional lung segmentation methods rely on large attenuation differences between lung parenchyma and surrounding tissue. These methods fail in scans where dense abnormalities are present, which often occurs in clinical data. Some methods to handle these situations have been proposed, but they are too time consuming or too specialized to be used in clinical practice. In this article, a new hybrid lung segmentation method is presented that automatically detects failures of a conventional algorithm and, when needed, resorts to a more complex...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: van Rikxoort EM, de Hoop B, Viergever MA, Prokop M, van Ginneken B Tags: Med Phys Source Type: journals

Temporal and dose dependence of T2 and ADC at 9.4 T in a mouse model following single fraction radiation therapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this study is to use magnetic resonance imaging to monitor the response of human glioma tumor xenografts to single fraction radiation therapy. Mice were divided into four treatment groups (n = 6 per group) that received 50, 200, 400, or 800 cGy of 200 kVp x rays. A fifth group (n = 6) received no radiation dose and served as the control. Quantitative maps of the treated tumor tissue were produced of water apparent diffusion coefficient (ADC) and transverse relaxation time (T2). Mice were imaged before and at multiple time points after treatment. There was a statistically significant difference in tumor g...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Larocque MP, Syme A, Yahya A, Wachowicz K, Allalunis-Turner J, Fallone BG Tags: Med Phys Source Type: journals

Diffraction and coherence in breast ultrasound tomography: a study with a toroidal array.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Ultrasound is commonly used as an adjunct to mammography for diagnostic evaluation of suspicions arising from breast cancer screening. As an alternative to conventional sonography that uses hand-held transducers, toroidal array probes that encircle the breast immersed in a water bath have been investigated for ultrasound tomography. In this paper, two sets of experiments performed with a prototype ultrasound scanner on a phantom and a human breast in vivo are used to investigate the effects of diffraction and coherence in ultrasound tomography. Reconstructions obtained with transmission diffraction tomography (TDT) are...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Simonetti F, Huang L, Duric N, Littrup P Tags: Med Phys Source Type: journals

An enhanced sector integration model for output and dose distribution calculation of irregular concave shaped electron beams.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A comprehensive method of output factor and dose distribution calculation for electron beams has been developed. It allows one to calculate the output factors and isodose distributions in water of arbitrary shaped electron fields with excellent accuracy even for the cases of concaved, small, elongated beams, and extended source to surface distances (SSDs). The method requires two sets of data: Depth dose distribution per monitor unit for circular cutouts and depth dose distributions per monitor unit for circular blocks (plugs), both for two SSDs, one reference of 100 cm and second extended one. The method has been exte...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Gajewski R Tags: Med Phys Source Type: journals

An adaptive incremental approach to constructing ensemble classifiers: application in an information-theoretic computer-aided decision system for detection of masses in mammograms.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Ensemble classifiers have been shown efficient in multiple applications. In this article, the authors explore the effectiveness of ensemble classifiers in a case-based computer-aided diagnosis system for detection of masses in mammograms. They evaluate two general ways of constructing subclassifiers by resampling of the available development dataset: Random division and random selection. Furthermore, they discuss the problem of selecting the ensemble size and propose two adaptive incremental techniques that automatically select the size for the problem at hand. All the techniques are evaluated with respect to a previou...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Mazurowski MA, Zurada JM, Tourassi GD Tags: Med Phys Source Type: journals

A self-checking fiber optic dosimeter for monitoring common errors in brachytherapy applications.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Scintillation dosimetry with optical fiber readout [fiber optic dosimetry (FOD)] requires accurate measurement of light intensity. It is therefore vulnerable to loss of calibration if any changes occur in the efficiency of the optical pathway between the scintillator and the light detector. The authors show in this article that common types of errors that arise during clinical use for brachytherapy applications can be quantified using a light emitting diode to stimulate the scintillator, the so-called LED-FOD method, in an integrated and easy-to-use control unit that incorporates a compact peripheral component intercon...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Yin Y, Lambert J, Yang S, McKenzie DR, Jackson M, Suchowerska N Tags: Med Phys Source Type: journals

Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beam dosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k(pl) for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4-18 MV photon beams. For electron beams, a depth-scaling factor c(pl) and a chamber-dependent fluence correction factor h(pl) for both phantoms were also calculated in combination with NACP-02 and Roos plane-para...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Araki F, Hanyu Y, Fukuoka M, Matsumoto K, Okumura M, Oguchi H Tags: Med Phys Source Type: journals

Differential dose volume histograms of Gamma knife in the presence of inhomogeneities using MRI-polymer gel dosimetry and MC simulation.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, EGSnrc calculated and PAGAT polymer gel dosimeter measured dose volume histograms (DVHs) for single-shot irradiations of the Gamma Knife (GK) unit were used to investigate the effects of the presence of inhomogeneities on 3D dose distribution. The head phantom was a custom-built 16 cm diameter Plexiglas sphere. Inside the phantom, there is a cubic cutout for inserting the gel vials and another cutout for inserting the inhomogeneities. Following irradiation with the GK unit, the polymer gel phantoms were scanned with a 1.5 T MRI scanner. Comparing the results of measurement in homogeneous and heterogeneous ph...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Pourfallah TA, Allahverdi M, Alam NR, Ay MR, Zahmatkesh MH Tags: Med Phys Source Type: journals

General strategy for the protection of organs at risk in IMRT therapy of a moving body.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We investigated protection strategies of organs at risk (OARs) in intensity modulated radiation therapy (IMRT). These strategies apply to delivery of IMRT to moving body anatomies that show relative displacement of OAR in close proximity to a tumor target. We formulated an efficient genetic algorithm which makes it possible to search for global minima in a complex landscape of multiple irradiation strategies delivering a given, predetermined intensity map to a target. The optimal strategy was investigated with respect to minimizing the dose delivered to the OAR. The optimization procedure developed relies on variabilit...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Abolfath RM, Papiez L Tags: Med Phys Source Type: journals

Optimal "image-based" weighting for energy-resolved CT.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper investigates a method of reconstructing images from energy-resolved CT data with negligible beam-hardening artifacts and improved contrast-to-nosie ratio (CNR) compared to conventional energy-weighting methods. Conceptually, the investigated method first reconstructs separate images from each energy bin. The final image is a linear combination of the energy-bin images, with the weights chosen to maximize the CNR in the final image. The optimal weight of a particular energy-bin image is derived to be proportional to the contrast-to-noise-variance ratio in that image. The investigated weighting method is refer...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Schmidt TG Tags: Med Phys Source Type: journals

Dosimetric properties of an amorphous-silicon EPID used in continuous acquisition mode for application to dynamic and arc IMRT.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Dosimetric properties of an amorphous-silicon electronic portal imaging device (EPID) operated in a real-time acquisition mode were investigated. This mode will be essential for time-resolved dose verification of dynamic (sliding window) intensity modulated radiation therapy (IMRT) and intensity modulated arc radiation therapy (arc-IMRT). The EPID was used in continuous acquisition mode (i.e., "cine" mode) where individual sequential image frames are acquired in real time. The properties studied include dose linearity, reproducibility of response, and image stability. Results of using the continuous acquisition mode wi...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: McCurdy BM, Greer PB Tags: Med Phys Source Type: journals

Lesion quantification in oncological positron emission tomography: a maximum likelihood partial volume correction strategy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A maximum likelihood (ML) partial volume effect correction (PVEC) strategy for the quantification of uptake and volume of oncological lesions in 18F-FDG positron emission tomography is proposed. The algorithm is based on the application of ML reconstruction on volumetric regional basis functions initially defined on a smooth standard clinical image and iteratively updated in terms of their activity and volume. The volume of interest (VOI) containing a previously detected region is segmented by a k-means algorithm in three regions: A central region surrounded by a partial volume region and a spill-out region. All volume...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: De Bernardi E, Faggiano E, Zito F, Gerundini P, Baselli G Tags: Med Phys Source Type: journals

Characteristics of Gafchromic XR-RV2 radiochromic film.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article investigates the dose response, energy response, postexposure growth, and polarizing effects of this film after exposure to ionizing radiation in the diagnostic energy range. The effect of bit depth on scanning was also investigated. Films were scanned using an Epson Expression 10000XL document scanner or an X-Rite model 301 spot densitometer. Color channel analysis was performed. The film showed usable response in the air kerma range of 1-1000 cGy, although by 1500 cGy the film appeared saturated when using the red color channel on a document scanner. The film response varied by 11% between 60 and 96 kVp and ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Blair A, Meyer J Tags: Med Phys Source Type: journals

Incorporating uncertainties in respiratory motion into 4D treatment plan optimization.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The purpose of this work is to investigate robust 4D optimization techniques which account for respiratory motion uncertainties. Two robust optimization techniques were applied to generate 4D optimized lung treatment plans. The probabilistic optimization approach minimizes the dose variance in the target volume while the worst case optimization minimizes a weighted combination of the nominal and worst case dose distributions which occur in the presence of respiratory motion variation. The two 4D optimization approaches were compared with a margin-based midventilation planning approach in five lung patients. Respiratory...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Heath E, Unkelbach J, Oelfke U Tags: Med Phys Source Type: journals

A practical way to improve contrast-to-noise ratio and quantitation for statistical-based iterative reconstruction in whole-body PET imaging.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study was performed on an IEC Body Phantom Set filled with 18F (sphere-to-background activity ratio: 4:1). The same 3 min acquisition was reconstructed with either (i) a clinical system based on a geometrical tomographic operator (OSEM_CL) or (ii) an OSEM algorithm using the suggested system matrix (OSEM_DR). In order to compare the resulting images, they set the 3D Gaussian postfilter (3DGPF) for OSEM_DR so as to obtain similar background signal-to-noise ratio (SNR) to that of OSEM_CL with a Gaussian postfilter full width at half maximum of 5 mm (as recommended for whole-body imaging on a Biograph6). They then assess...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Fin L, Bailly P, Daouk J, Meyer ME Tags: Med Phys Source Type: journals

Dosimetric comparison of four new design 103Pd brachytherapy sources: optimal design using silver and copper rod cores.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, the optimal source IRA3-103Pd provides the most isotropic dose distribution in water with the dose rate constant of 0.678(+/-0.1%) cGy h(-1) U(-1). The IRA3-103Pd design has a silver rod core combined with thin-wall, concave end caps. Finally, the authors compared the results for their optimal source with published results for those of other source manufacturers. PMID: 19673207 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Hosseini SH, Sadeghi M, Ataeinia V Tags: Med Phys Source Type: journals

Computer-aided diagnosis of pulmonary nodules on CT scans: improvement of classification performance with nodule surface features.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study demonstrated that the authors' proposed segmentation and feature extraction techniques are promising for classifying lung nodules on CT images. PMID: 19673208 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Way TW, Sahiner B, Chan HP, Hadjiiski L, Cascade PN, Chughtai A, Bogot N, Kazerooni E Tags: Med Phys Source Type: journals

Quantitative contrast-enhanced myocardial perfusion magnetic resonance imaging: simulation of bolus dispersion in constricted vessels.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Quantification of myocardial blood flow (MBF) by means of T1-weighted first-pass magnetic resonance imaging (MRI) requires knowledge of the arterial input function (AIF), which is usually estimated from the left ventricle (LV). Dispersion of the contrast agent bolus may occur between the LV and the tissue of interest, which leads to systematic underestimation of the MBF. The aim of this study was to simulate the dispersion along a simplified coronary artery with different stenoses. To analyze the dispersion in vessels with typical dimensions of coronary arteries, simulations were performed using the computational fluid...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Graafen D, Münnemann K, Weber S, Kreitner KF, Schreiber LM Tags: Med Phys Source Type: journals

Quantitative CT of lung nodules: dependence of calibration on patient body size, anatomic region, and calibration nodule size for single- and dual-energy techniques.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Calcium concentration may be a useful feature for distinguishing benign from malignant lung nodules in computer-aided diagnosis. The calcium concentration can be estimated from the measured CT number of the nodule and a CT number vs calcium concentration calibration line that is derived from CT scans of two or more calcium reference standards. To account for CT number nonuniformity in the reconstruction field, such calibration lines may be obtained at multiple locations within lung regions in an anthropomorphic phantom. The authors performed a study to investigate the effects of patient body size, anatomic region, and ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Goodsitt MM, Chan HP, Way TW, Schipper MJ, Larson SC, Christodoulou EG Tags: Med Phys Source Type: journals

Methodology for generating a 3D computerized breast phantom from empirical data.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The initial process for creating a flexible three-dimensional computer-generated breast phantom based on empirical data is described. Dedicated breast computed-tomography data were processed to suppress noise and scatter artifacts in the reconstructed image set. An automated algorithm was developed to classify the breast into its primary components. A preliminary phantom defined using subdivision surfaces was generated from the segmented data. To demonstrate potential applications of the phantom, simulated mammographic image data were acquired of the phantom using a simplistic compression model and an analytic projecti...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Li CM, Segars WP, Tourassi GD, Boone JM, Dobbins JT Tags: Med Phys Source Type: journals

Monte Carlo modeling of small photon fields: quantifying the impact of focal spot size on source occlusion and output factors, and exploring miniphantom design for small-field measurements.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The accuracy with which Monte Carlo models of photon beams generated by linear accelerators (linacs) can describe small-field dose distributions depends on the modeled width of the electron beam profile incident on the linac target. It is known that the electron focal spot width affects penumbra and cross-field profiles; here, the authors explore the extent to which source occlusion reduces linac output for smaller fields and larger spot sizes. A BEAMnrc Monte Carlo linac model has been used to investigate the variation in penumbra widths and small-field output factors with electron spot size. A formalism is developed ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Scott AJ, Nahum AE, Fenwick JD Tags: Med Phys Source Type: journals

An analytical approach to estimating the first order x-ray scatter in heterogeneous medium.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
X-ray scatter estimation in heterogeneous medium is a challenge in improving the quality of diagnostic projection images and volumetric image reconstruction. For Compton scatter, the statistical behavior of the first order scatter can be accurately described by using the Klein-Nishina expression for Compton scattering cross section provided that the exact information of the medium including the geometry and the attenuation, which in fact is unknown, is known. The authors present an approach to approximately separate the unknowns from the Klein-Nishina formula and express the unknown part by the primary x-ray intensity ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Yao W, Leszczynski KW Tags: Med Phys Source Type: journals

An analytical approach to estimating the first order scatter in heterogeneous medium. II. A practical application.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Recently, the authors proposed an analytical scheme to estimate the first order x-ray scatter by approximating the Klein-Nishina formula so that the first order scatter fluence is expressed as a function of the primary photon fluence on the detector. In this work, the authors apply the scheme to experimentally obtained 6 MV cone beam CT projections in which the primary photon fluence is the unknown of interest. With the assumption that the higher-order scatter fluence is either constant or proportional to the first order scatter fluence, an iterative approach is proposed to estimate both primary and scatter fluences fr...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Yao W, Leszczynski KW Tags: Med Phys Source Type: journals

Prospective cardiac gating of carotid three-dimensional ultrasound.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Quantitative measurements of carotid atherosclerosis can be determined using three-dimensional ultrasound (3DUS). This pilot study involved the development of prospective cardiac gating of 3DUS carotid images to reduce cardiac cycle-derived arterial pulsatility. The method developed uses electrocardiograph signal detection of the cardiac cycle R wave with imaging acquisition delayed in time (deltat) after the R wave is detected. Pulsatility of the common carotid artery was measured by calculating the mean percentage change in arterial cross-sectional area (%deltaA) in moderate atherosclerosis (MA) patients (12% +/- 1%)...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Mallett C, Gardi L, Fenster A, Parraga G Tags: Med Phys Source Type: journals

RSA calibration accuracy of a fluoroscopy-based system using nonorthogonal images for measuring functional kinematics.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study also showed that RSA may be performed with imaging devices at relative angles other than 90 degrees without compromising accuracy. This allows researchers greater freedom in positioning equipment. PMID: 19673216 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Kedgley AE, Jenkyn TR Tags: Med Phys Source Type: journals

The accuracy of the pencil beam convolution and anisotropic analytical algorithms in predicting the dose effects due to attenuation from immobilization devices and large air gaps.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
When a photon beam passes through the treatment couch or an immobilization device, it may traverse a large air gap (up to 15 cm or more) prior to entering the patient. Previous studies have investigated the ability of various treatment planning systems to calculate the dose immediately beyond small air gaps, typically less than 5 cm thick, such as those within the body. The aim of this study is to investigate the ability of the Eclipse anisotropic analytical algorithm (AAA) and pencil beam convolution (PBC) algorithm to calculate the dose beyond large air gaps. Depth dose data in water for a 6 MV photon beam, 10 x 10 c...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Gray A, Oliver LD, Johnston PN Tags: Med Phys Source Type: journals

STEP: spatiotemporal enhancement pattern for MR-based breast tumor diagnosis.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article presents two major contributions. First, the STEP features are introduced to capture temporal enhancement and its spatial variations. This is essentially carried out through the Fourier transformation and pharmacokinetic modeling of various temporal enhancement features, followed by the calculation of moment invariants and Gabor texture features. Second, for effectively extracting the STEP features from tumors, we develop a graph-cut based segmentation algorithm that aims at refining coarse manual segmentations of tumors. The STEP features are assessed through their diagnostic performance for differentiating b...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Zheng Y, Englander S, Baloch S, Zacharaki EI, Fan Y, Schnall MD, Shen D Tags: Med Phys Source Type: journals

Field size dependence of the output factor in passively scattered proton therapy: influence of range, modulation, air gap, and machine settings.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
At the Francis H. Burr Proton Therapy Center field specific output factors (i.e., dose per monitor unit) for patient treatments were modeled for all beamlines (two gantries, fixed stereotactic, and fixed eye beamline). The authors evaluated the accuracy of dose calculation and output model for small fields. Measurements in a water phantom were performed in three of our beamlines quantifying the dependency of the output factor on the field size for a variety of proton ranges. The influence of snout size, air gap, modulation, and second scatterer was investigated. The impact of field size on output depends strongly on th...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Daartz J, Engelsman M, Paganetti H, Bussière MR Tags: Med Phys Source Type: journals

Mapping structural changes in breast tissue disease using x-ray scattering.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spread of invasive carcinoma throughout breast tissue is believed to occur at supramolecular levels, beyond the range of standard histopathology identification. Small angle x-ray scattering (SAXS) is capable of characterizing the structural properties of collagen and tissue found in the breast at the scale of tens to hundreds of nanometers. Fifty-six patients who were treated with wide-local excision or mastectomy had tissue biopsy samples analyzed at 2 cm intervals along two perpendicular axes over their excised mass, up to 6 cm away from the primary site of the tumor. Two SAXS parameters, the integrated amorphous sca...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Sidhu S, Siu KK, Falzon G, Hart SA, Foxe JG, Lewis RA Tags: Med Phys Source Type: journals

Objective index of image fidelity for JPEG2000 compressed body CT images.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In conclusion, the CR is less suitable than the PSNR or HDR-VDP as an objective index of image fidelity for JPEG2000 compressed body CT images. The HDR-VDP is more promising than the PSNR as such an index. PMID: 19673221 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Kim KJ, Lee KH, Kang HS, Kim SY, Kim YH, Kim B, Seo J, Mantiuk R Tags: Med Phys Source Type: journals

A monte Carlo investigation of Sw. noise for thick, segmented, crystalline scintillators for radiotherapy imaging.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, Monte Carlo simulations of radiation and optical transport have been used to examine I(opt) and zero-frequency DQE for segmented CsI:Tl and BGO detectors at different thicknesses and element-to-element pitches. For these detectors, I(opt) and DQE were studied as a function of various optical parameters, including absorption and scattering in the scintillator, absorption at the top reflector and septal walls, as well as scattering at the side surfaces of the scintillator crystals. The results indicate that I(opt) and DQE are only weakly affected by absorption and scattering in the scintillator, as well as by ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Wang Y, Antonuk LE, El-Mohri Y, Zhao Q Tags: Med Phys Source Type: journals

Recommendations for clinical electron beam dosimetry: supplement to the recommendations of Task Group 25.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The goal of Task Group 25 (TG-25) of the Radiation Therapy Committee of the American Association of.Physicists in Medicine (AAPM) was to provide a methodology and set of procedures for a medical physicist performing clinical electron beam dosimetry in the nominal energy range of 5-25 MeV. Specifically, the task group recommended procedures for acquiring basic information required for acceptance testing and treatment planning of new accelerators with therapeutic electron beams. Since the publication of the TG-25 report, significant advances have taken place in the field of electron beam dosimetry, the most significant b...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Gerbi BJ, Antolak JA, Deibel FC, Followill DS, Herman MG, Higgins PD, Huq MS, Mihailidis DN, Yorke ED, Hogstrom KR, Khan FM Tags: Med Phys Source Type: journals

Classification of trabeculae into three-dimensional rodlike and platelike structures via local inertial anisotropy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Trabecular bone microarchitecture is a significant determinant of the bone's mechanical properties and is thus of major clinical relevance in predicting fracture risk. The three-dimensional nature of trabecular bone is characterized by parameters describing scale, topology, and orientation of structural elements. However, none of the current methods calculates all three types of parameters simultaneously and in three dimensions. Here the authors present a method that produces a continuous classification of voxels as belonging to platelike or rodlike structures that determines their orientation and estimates their thick...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Vasilić B, Rajapakse CS, Wehrli FW Tags: Med Phys Source Type: journals

An approach to multiobjective optimization of rotational therapy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Multiobjective optimization is used in radiotherapy, especially IMRT, to generate treatment plans which meet different objectives to varying extents. Trade-off surfaces can be constructed representing the gains and losses of different objectives when switching from one plan to another, and the planner can interactively explore different treatment possibilities without the need for reoptimization. In this work a method for the multiobjective optimization of rotational therapy is introduced. The proposed method is applied slice per slice and uses the geometry of the slice directly to construct several arcs, each conforma...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Pardo-Montero J, Fenwick JD Tags: Med Phys Source Type: journals

Tolerances on MLC leaf position accuracy for IMRT delivery with a dynamic MLC.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study provides guidance, based on a dosimetric surrogate of clinical outcome, for the development of one component, leaf position accuracy of performance standards for multileaf collimators. PMID: 19673226 [PubMed - in process] (Source: Medical Physics)
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Rangel A, Dunscombe P Tags: Med Phys Source Type: journals

A simple backprojection algorithm for 3D in vivo EPID dosimetry of IMRT treatments.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Treatment plans are usually designed, optimized, and evaluated based on the total 3D dose distribution, motivating a total 3D dose verification. The purpose of this study was to develop a 2D transmission-dosimetry method using an electronic portal imaging device (EPID) into a simple 3D method that provides 3D dose information. In the new method, the dose is reconstructed within the patient volume in multiple planes parallel to the EPID for each gantry angle. By summing the 3D dose grids of all beams, the 3D dose distribution for the total treatment fraction is obtained. The algorithm uses patient contours from the plan...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Wendling M, McDermott LN, Mans A, Sonke JJ, van Herk M, Mijnheer BJ Tags: Med Phys Source Type: journals

An investigation of signal performance enhancements achieved through innovative pixel design across several generations of indirect detection, active matrix, flat-panel arrays.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Active matrix flat-panel imager (AMFPI) technology is being employed for an increasing variety of imaging applications. An important element in the adoption of this technology has been significant ongoing improvements in optical signal collection achieved through innovations in indirect detection array pixel design. Such improvements have a particularly beneficial effect on performance in applications involving low exposures and/or high spatial frequencies, where detective quantum efficiency is strongly reduced due to the relatively high level of additive electronic noise compared to signal levels of AMFPI devices. In ...
Source: Medical Physics - June 30, 2009 Category: Physics Authors: Antonuk LE, Zhao Q, El-Mohri Y, Du H, Wang Y, Street RA, Ho J, Weisfield R, Yao W Tags: Med Phys Source Type: journals