AAPM Banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Sep 2010

Volume 37, Issue 9, pp. 4525-5148

Page 1 of 7 Pages Next Page | Jump to Page

EDITORIAL: New web platform for Medical Physics

Bill Hendee, Editor

Med. Phys. 37, 4525 (2010); http://dx.doi.org/10.1118/1.3483005 (1 page) | Cited 1 time

Online Publication Date: 5 August 2010

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
01.10.Cr Announcements, news, and awards

POINT/COUNTERPOINT: Ultrasonography is soon likely to become a viable alternative to x-ray mammography for breast cancer screening

Carri K. Glide-Hurst, Ph.D., Andrew D. A. Maidment, Ph.D., and Colin G. Orton, Ph.D., Moderator

Med. Phys. 37, 4526 (2010); http://dx.doi.org/10.1118/1.3459019 (4 pages)

Online Publication Date: 5 August 2010

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
87.63.dh Ultrasonographic imaging
87.59.E- Mammography
87.19.xj Cancer

RADIATION THERAPY PHYSICS: Automated registration of diagnostic to prediagnostic x-ray mammograms: Evaluation and comparison to radiologists’ accuracy

Snehal M. Pinto Pereira, John H. Hipwell, Valerie A. McCormack, Christine Tanner, Sue M. Moss, Louise S. Wilkinson, Lisanne A. L. Khoo, Catriona Pagliari, Pippa L. Skippage, Carole J. Kliger, David J. Hawkes, and Isabel M. dos Santos Silva

Med. Phys. 37, 4530 (2010); http://dx.doi.org/10.1118/1.3457470 (10 pages)

Online Publication Date: 5 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: To compare and evaluate intensity-based registration methods for computation of serial x-ray mammogram correspondence.
Methods: X-ray mammograms were simulated from MRIs of 20 women using finite element methods for modeling breast compressions and employing a MRI/x-ray appearance change model. The parameter configurations of three registration methods, affine, fluid, and free-form deformation (FFD), were optimized for registering x-ray mammograms on these simulated images. Five mammography film readers independently identified landmarks (tumor, nipple, and usually two other normal features) on pairs of diagnostic and corresponding prediagnostic digitized images from 52 breast cancer cases. Landmarks were independently reidentified by each reader. Target registration errors were calculated to compare the three registration methods using the reader landmarks as a gold standard. Data were analyzed using multilevel methods.
Results: Between-reader variability varied with landmark (p<0.01) and screen (p = 0.03), with between-reader mean distance (mm) in point location on the diagnostic/prediagnostic images of 2.50 (95% CI 1.95, 3.15)/2.84 (2.24, 3.55) for nipples and 4.26 (3.43, 5.24)/4.76 (3.85, 5.84) for tumors. Registration accuracy was sensitive to the type of landmark and the amount of breast density. For dense breasts ( ≥ 40%), the affine and fluid methods outperformed FFD. For breasts with lower density, the affine registration surpassed both fluid and FFD. Mean accuracy (mm) of the affine registration varied between 3.16 (95% CI 2.56, 3.90) for nipple points in breasts with density 20%–39% and 5.73 (4.80, 6.84) for tumor points in breasts with density <20%.
Conclusions: Affine registration accuracy was comparable to that between independent film readers. More advanced two-dimensional nonrigid registration algorithms were incapable of increasing the accuracy of image alignment when compared to affine registration.
Show PACS
87.61.-c Magnetic resonance imaging
87.59.B- Radiography
87.59.E- Mammography
87.57.nj Registration
87.19.xj Cancer
87.10.Kn Finite element calculations

THERMOTHERAPY PHYSICS: Optimization in hyperthermia treatment planning: The impact of tissue perfusion uncertainty

M. de Greef, H. P. Kok, D. Correia, A. Bel, and J. Crezee

Med. Phys. 37, 4540 (2010); http://dx.doi.org/10.1118/1.3462561 (11 pages) | Cited 6 times

Online Publication Date: 5 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: Hyperthermia treatment planning (HTP) potentially provides a valuable tool for monitoring and optimization of treatment. However, one of the major problems in HTP is that different sources of uncertainty degrade its reliability. Perfusion uncertainty is one of the largest uncertainties and hence there is an ongoing debate whether optimization should be limited to power-based strategies. In this study a systematic analysis is carried out addressing this question.
Methods: The influence of perfusion uncertainty on optimization was analyzed for five patients with cervix uteri carcinoma heated with the AMC-8 70 MHz phased-array waveguide system. The effect of variations (up to ±50%) in both the muscle and tumor perfusion level was investigated. For every patient, reference solutions were calculated using constrained temperature-based optimization for 25 different and known perfusion distributions. Reference solutions were compared to those found by temperature-based optimization using standard perfusion values and four SAR-based optimization methods. The effect of heterogeneity was investigated by creating 5×100 perfusion distributions for different levels of local variation (±25% and ±50%) and scale (1 and 2 cm). Here the performance of the temperature-based optimization method was compared to a SAR-based method that showed good performance in the previous analysis.
Results: Solutions found with temperature-based optimization using a deviating perfusion distribution during optimization were found within 1.0 °C from the true optimum. For the SAR-based methods, deviations up to 2.9 °C were found. The spread found in these deviations was comparable, typically 0.5–1.0 °C. When applying intramuscle variation to the perfusion, temperature-based optimization proved to be the best strategy in 95% of the evaluated cases applying ±50% local variation.
Conclusions: Temperature-based optimization proves to be superior to SAR-based optimization both under variation of perfusion level as well as under the application of intratissue variation. The spread in achieved temperatures is comparable. These results are valid under the assumption of constant perfusion at hyperthermic levels. Although similar results are expected from models including thermoregulation, additional analysis is required to confirm this. In view of uncertainty in tissue perfusion and other modeling uncertainties, the authors propose feedback guided temperature-based optimization as the best candidate to improve thermal dose delivery during hyperthermia treatment.
Show PACS
87.19.Pp Biothermics and thermal processes in biology
87.55.-x Treatment strategy

OPTICAL PHYSICS: Fast-MICP for frameless image-guided surgery

Jiann-Der Lee, Chung-Hsien Huang, Sheng-Ta Wang, Chung-Wei Lin, and Shin-Tseng Lee

Med. Phys. 37, 4551 (2010); http://dx.doi.org/10.1118/1.3470097 (9 pages) | Cited 3 times

Online Publication Date: 6 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: In image-guided surgery (IGS) systems, image-to-physical registration is critical for reliable anatomical information mapping and spatial guidance. Conventional stereotactic frame-based or fiducial-based approaches provide accurate registration but are not patient-friendly. This study proposes a frameless cranial IGS system that uses computer vision techniques to replace the frame or fiducials with the natural features of the patient.
Methods: To perform a cranial surgery with the proposed system, the facial surface of the patient is first reconstructed by stereo vision. Accuracy is ensured by capturing parallel-line patterns projected from a calibrated LCD projector. Meanwhile, another facial surface is reconstructed from preoperative computed tomography (CT) images of the patient. The proposed iterative closest point (ICP)-based algorithm [fast marker-added ICP (Fast-MICP)] is then used to register the two facial data sets, which transfers the anatomical information from the CT images to the physical space.
Results: Experimental results reveal that the Fast-MICP algorithm reduces the computational cost of marker-added ICP ( J.-D. Lee et al., “A coarse-to-fine surface registration algorithm for frameless brain surgery,” in Proceedings of International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, pp. 836–839 ) to 10% and achieves comparable registration accuracy, which is under 3 mm target registration error (TRE). Moreover, two types of optical-based spatial digitizing devices can be integrated for further surgical navigation. Anatomical information or image-guided surgical landmarks can be projected onto the patient to obtain an immersive augmented reality environment.
Conclusion: The proposed frameless IGS system with stereo vision obtains TRE of less than 3 mm. The proposed Fast-MICP registration algorithm reduces registration time by 90% without compromising accuracy.
Show PACS
87.57.nj Registration
87.57.nf Reconstruction
87.57.Q- Computed tomography
87.59.-e X-ray imaging
87.85.Pq Biomedical imaging

RADIATION IMAGING PHYSICS: Deformable image registration of heterogeneous human lung incorporating the bronchial tree

Adil Al-Mayah, Joanne Moseley, Mike Velec, Shannon Hunter, and Kristy Brock

Med. Phys. 37, 4560 (2010); http://dx.doi.org/10.1118/1.3471020 (12 pages) | Cited 3 times

Online Publication Date: 6 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: To investigate the effect of the bronchial tree on the accuracy of biomechanical-based deformable image registration of human lungs.
Methods: Three dimensional finite element models have been developed using four dimensional computed tomography image data of ten lung cancer patients. Each model is built of a body, left and right lungs, tumor, and bronchial trees. Triangular shell elements are used for the bronchial trees while tetrahedral elements are used for other components. Hyperelastic material properties based on experimental investigation on human lungs are used for the lung parenchyma. Different material properties are assigned for the bronchial tree using five values for the modulus of elasticity of 0.01, 0.12, 0.5, 10, and 18 MPa. Lungs are modeled to slide inside chest cavities by applying frictionless contact surfaces between each lung and corresponding chest cavity. The accuracy of the models is examined using an average of 40 bronchial bifurcation points identified on inhale and exhale images. Relative accuracy is evaluated by comparing the displacement of all nodes within the lungs as well as the dosimetric difference at the exhale position predicted by the model.
Results: There is no significant effect of bronchial tree on the model accuracy based on the bifurcation points analysis. However, on the local level, using an average of 38 000 nodes, there is a maximum difference of 8.5 mm in the deformation of the bronchial trees, as the modulus of elasticity of the bronchial trees increases from 0.01 to 18 MPa; however, more than 96% of nodes are within a 2.5 mm difference in each direction. The average dose difference at the predicted exhale position is less than 35 cGy between the models.
Conclusions: The bronchial tree has little effect on the global deformation and the accuracy of deformable image registration of lungs. Hence, the homogenous model is a reasonable assumption. Since there are some local deformation differences between nodes as the material properties of the bronchial tree change that may affect the accuracy of dosimetric results, heterogeneity may be required for a smaller scale modeling of lungs.
Show PACS
87.57.nj Registration
87.59.-e X-ray imaging
87.85.jc Electrical, thermal, and mechanical properties of biological matter
87.19.rd Elastic properties
87.19.xj Cancer
87.57.Q- Computed tomography

RADIATION IMAGING PHYSICS: Semiautomatic technique for defining the internal gross tumor volume of lung tumors close to liver/spleen cupola by 4D-CT

Pietro Mancosu, Roberto Sghedoni, Valentino Bettinardi, Mark Anthony Aquilina, Piera Navarria, Giovanni Mauro Cattaneo, Nadia Di Muzio, Luca Cozzi, and Marta Scorsetti

Med. Phys. 37, 4572 (2010); http://dx.doi.org/10.1118/1.3471379 (5 pages) | Cited 3 times

Online Publication Date: 6 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: It has been shown that in cases of lung tumors close to the liver cupola, the four dimensional (4D)-CT postprocessing maximum intensity projection (MIP) algorithm does not fully recover the radiotherapy internal gross tumor volume (IGTV). In this work, a semiautomatic technique was evaluated by which the residual IGTV that was not included into the IGTV by MIP algorithm was actually added.
Methods: A moving phantom and five selected patients were considered. The various IGTVs produced by the semiautomatic approach were compared to those generated by 4D-CT manual contouring.
Results: In all cases, the radiation oncologist qualitatively concurred with the semiautomatic IGTV. A quantitative difference in volume of 2.6% was found in the phantom study, whereas a mean difference of 0.1±4.6% was obtained in the patient studies.
Conclusions: A semiautomatic technique to include the residual part of IGTV covered by liver/spleen cupola when using MIP algorithm was validated on phantom and on selected patients, revealing the possibility of defining the IGTV for patients with lesions located near liver/spleen cupola by performing only the contours on the MIP series.
Show PACS
87.55.D- Treatment planning
87.57.Q- Computed tomography
87.56.-v Radiation therapy equipment

MAGNETIC RESONANCE PHYSICS: Design of iterative ROI transmission tomography reconstruction procedures and image quality analysis

Benoit Hamelin, Yves Goussard, Jean-Pierre Dussault, Guy Cloutier, Gilles Beaudoin, and Gilles Soulez

Med. Phys. 37, 4577 (2010); http://dx.doi.org/10.1118/1.3447722 (13 pages) | Cited 2 times

Online Publication Date: 6 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: An iterative edge-preserving CT reconstruction algorithm for high-resolution imaging of small regions of the field of view is investigated. It belongs to a family of region-of-interest reconstruction techniques in which a low-cost pilot reconstruction of the whole field of view is first performed and then used to deduce the contribution of the region of interest to the projection data. These projections are used for a high-resolution reconstruction of the region of interest (ROI) using a regularized iterative algorithm, resulting in significant computational savings. This paper examines how the technique by which the pilot reconstruction of the full field of view is obtained affects the total runtime and the image quality in the region of interest.
Methods: Previous contributions to the literature have each focused on a single approach for the pilot reconstruction. In this paper, two such approaches are compared: the filtered backprojection and a low-resolution regularized iterative reconstruction method. ROI reconstructions are compared in terms of image quality and computational cost over simulated and physical phantom (Catphan600©) studies, in order to assess the compromises that most impact the quality of the ROI reconstruction.
Results: With the simulated phantom, new artifacts that appear in the ROI images are caused by significant errors in the pilot reconstruction. These errors include excessive coarseness of the pilot image grid and beam-hardening artifacts. With the Catphan600 phantom, differences in the imaging model of the scanner and that of the iterative reconstruction algorithm cause dark border artifacts in the ROI images.
Conclusions: Inexpensive pilot reconstruction techniques (analytical algorithms, very-coarse-grid penalized likelihood) are practical choices in many common cases. However, they may yield background images altered by edge degradation or beam hardening, inducing projection inconsistency in the data used for ROI reconstruction. The ROI images thus have significant streak and speckle artifacts, which adversely affect the resolution-to-noise compromise. In these cases, edge-preserving penalized-likelihood methods on not-too-coarse image grids prove to be more robust and provide the best ROI image quality.
Show PACS
87.57.cp Artifacts and distortion
87.57.nf Reconstruction
87.57.nt Edge enhancement
87.57.Q−

RADIATION THERAPY PHYSICS: Spatially weighted mutual information image registration for image guided radiation therapy

Samuel B. Park, Frank C. Rhee, James I. Monroe, and Jason W. Sohn

Med. Phys. 37, 4590 (2010); http://dx.doi.org/10.1118/1.3463609 (12 pages) | Cited 3 times

Online Publication Date: 10 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: To develop a new metric for image registration that incorporates the (sub)pixelwise differential importance along spatial location and to demonstrate its application for image guided radiation therapy (IGRT).
Methods: It is well known that rigid-body image registration with mutual information is dependent on the size and location of the image subset on which the alignment analysis is based [the designated region of interest (ROI)]. Therefore, careful review and manual adjustments of the resulting registration are frequently necessary. Although there were some investigations of weighted mutual information (WMI), these efforts could not apply the differential importance to a particular spatial location since WMI only applies the weight to the joint histogram space. The authors developed the spatially weighted mutual information (SWMI) metric by incorporating an adaptable weight function with spatial localization into mutual information. SWMI enables the user to apply the selected transform to medically “important” areas such as tumors and critical structures, so SWMI is neither dominated by, nor neglects the neighboring structures. Since SWMI can be utilized with any weight function form, the authors presented two examples of weight functions for IGRT application: A Gaussian-shaped weight function (GW) applied to a user-defined location and a structures-of-interest (SOI) based weight function. An image registration example using a synthesized 2D image is presented to illustrate the efficacy of SWMI. The convergence and feasibility of the registration method as applied to clinical imaging is illustrated by fusing a prostate treatment planning CT with a clinical cone beam CT (CBCT) image set acquired for patient alignment. Forty-one trials are run to test the speed of convergence. The authors also applied SWMI registration using two types of weight functions to two head and neck cases and a prostate case with clinically acquired CBCT/MVCT image sets. The SWMI registration with a Gaussian weight function (SWMI-GW) was tested between two different imaging modalities: CT and MRI image sets.
Results: SWMI-GW converges 10% faster than registration using mutual information with an ROI. SWMI-GW as well as SWMI with SOI-based weight function (SWMI-SOI) shows better compensation of the target organ’s deformation and neighboring critical organs’ deformation. SWMI-GW was also used to successfully fuse MRI and CT images.
Conclusions: Rigid-body image registration using our SWMI-GW and SWMI-SOI as cost functions can achieve better registration results in (a) designated image region(s) as well as faster convergence. With the theoretical foundation established, we believe SWMI could be extended to larger clinical testing.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
87.57.Q- Computed tomography
87.61.-c Magnetic resonance imaging
87.57.nj Registration
87.19.xj Cancer

THERMOTHERAPY PHYSICS: Near-field radiofrequency thermoacoustic tomography with impulse excitation

Daniel Razansky, Stephan Kellnberger, and Vasilis Ntziachristos

Med. Phys. 37, 4602 (2010); http://dx.doi.org/10.1118/1.3467756 (6 pages) | Cited 2 times

Online Publication Date: 10 August 2010

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Purpose: Imaging performance of radiofrequency and microwave-based thermoacoustic tomography systems is mainly determined by the ability to deposit a substantial amount of electromagnetic energy within ultrashort time duration. Pulses of nanosecond-range duration that can carry hundreds of millijoules energy are ideal for obtaining good signal-to-noise and spatial resolution in many biological imaging applications. However, existing implementations are based on modulated-carrier-frequency amplification solutions, which are generally costly and cannot achieve ultrahigh-peak-power requirements essential for optimal thermoacoustic signal generation.
Methods: Herein the authors suggest and experimentally validate a near-field radiofrequency tomography (NRT) method for high resolution imaging of biological tissues using ultrashort electromagnetic impulses. The solution includes a low-cost pulsing system while the imaged objects are placed in the near field of the energy-emitting aperture for improved coupling using nonradiative fields.
Results: In the current design, the authors were able to achieve excitation impulse energies of hundreds of millijoules with durations in the order of a few nanoseconds, corresponding to peak power levels of multiple megawatts. The phantom imaging experiments demonstrated image features with characteristic sizes of around 170 μm, but the impulse durations used herein allow in principle spatial resolutions in the order of a few tens of microns when using an appropriate ultrasonic detection bandwidth.
Conclusions: The proposed NRT method makes it possible to attain very high spatial resolution without compromising the thermoacoustic signal strength. This makes the imaging performance to be limited by the available bandwidth of the ultrasonic detector rather than by the microwave pulse duration. It is overall expected that the combination of pulsed near-field coupling with optimal choice of energy dissipation elements will generate a practical modality that can scale its application to small and larger volumes alike, while optimally adjusting the resolution to match the acoustic resolution possible. Such an approach should find several applications in small animal and clinical imaging.
Show PACS
87.63.dh Ultrasonographic imaging
87.85.Ng Biological signal processing
87.50.S- Radiofrequency/microwave fields effects
87.19.Pp Biothermics and thermal processes in biology
Page 1 of 7 Pages Next Page | Jump to Page
Close

Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
William R. Hendee, Editor
Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
One Physics Ellipse
College Park, Maryland 20740
301-209-3352

© 2012, American Association of Physicists in Medicine. Individual readers of this journal, and nonprofit libraries acting for them, are freely permited to make fair use of the material in it, such as to copy an article for use in teaching or research. (For other kinds of copying see "Copying Fees.") Permission is granted to quote from this journal in scientific works with the customary acknowledgment of the source. To reprint a figure, table, or other excerpt requires, in addition, AAPM may require that permission also be obtained from one of the authors. Address inquiries and notices to Penny Slattery, Journal Manager, Medical Physics Journal, AAPM, One Physics Ellipse, College Park, MD 20740-3846; email: journal@aapm.org.

close