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Dec 2007

Volume 34, Issue 12, pp. 4563-4980

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POINT/COUNTERPOINT: Kilovoltage imaging is more suitable than megavoltage imaging for guiding radiation therapy

Lei Xing, Ph.D., Jenghwa Chang, Ph.D., and Colin G. Orton, Ph.D., Moderator

Med. Phys. 34, 4563 (2007); http://dx.doi.org/10.1118/1.2799489 (4 pages) | Cited 2 times

Online Publication Date: 9 November 2007

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Abstract Unavailable
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87.59.-e X-ray imaging
87.53.-j Effects of ionizing radiation on biological systems
87.56.-v Radiation therapy equipment

RADIATION IMAGING PHYSICS: Automatic multiscale enhancement and segmentation of pulmonary vessels in CT pulmonary angiography images for CAD applications

Chuan Zhou, Heang-Ping Chan, Berkman Sahiner, Lubomir M. Hadjiiski, Aamer Chughtai, Smita Patel, Jun Wei, Jun Ge, Philip N. Cascade, and Ella A. Kazerooni

Med. Phys. 34, 4567 (2007); http://dx.doi.org/10.1118/1.2804558 (11 pages) | Cited 10 times

Online Publication Date: 9 November 2007

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The authors are developing a computerized pulmonary vessel segmentation method for a computer-aided pulmonary embolism (PE) detection system on computed tomographic pulmonary angiography (CTPA) images. Because PE only occurs inside pulmonary arteries, an automatic and accurate segmentation of the pulmonary vessels in 3D CTPA images is an essential step for the PE CAD system. To segment the pulmonary vessels within the lung, the lung regions are first extracted using expectation-maximization (EM) analysis and morphological operations. The authors developed a 3D multiscale filtering technique to enhance the pulmonary vascular structures based on the analysis of eigenvalues of the Hessian matrix at multiple scales. A new response function of the filter was designed to enhance all vascular structures including the vessel bifurcations and suppress nonvessel structures such as the lymphoid tissues surrounding the vessels. An EM estimation is then used to segment the vascular structures by extracting the high response voxels at each scale. The vessel tree is finally reconstructed by integrating the segmented vessels at all scales based on a “connected component” analysis. Two CTPA cases containing PEs were used to evaluate the performance of the system. One of these two cases also contained pleural effusion disease. Two experienced thoracic radiologists provided the gold standard of pulmonary vessels including both arteries and veins by manually tracking the arterial tree and marking the center of the vessels using a computer graphical user interface. The accuracy of vessel tree segmentation was evaluated by the percentage of the “gold standard” vessel center points overlapping with the segmented vessels. The results show that 96.2% (2398/2494) and 96.3% (1910/1984) of the manually marked center points in the arteries overlapped with segmented vessels for the case without and with other lung diseases. For the manually marked center points in all vessels including arteries and veins, the segmentation accuracy are 97.0% (4546/4689) and 93.8% (4439/4732) for the cases without and with other lung diseases, respectively. Because of the lack of ground truth for the vessels, in addition to quantitative evaluation of the vessel segmentation performance, visual inspection was conducted to evaluate the segmentation. The results demonstrate that vessel segmentation using our method can extract the pulmonary vessels accurately and is not degraded by PE occlusion to the vessels in these test cases.
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87.59.Dj Angiography
87.59.bd Computed radiography
87.57.C- Image quality
87.19.X- Diseases
02.10.Yn Matrix theory

RADIATION THERAPY PHYSICS: Monte Carlo investigation of breast intraoperative radiation therapy with metal attenuator plates

A. Martignano, L. Menegotti, and A. Valentini

Med. Phys. 34, 4578 (2007); http://dx.doi.org/10.1118/1.2805089 (7 pages) | Cited 2 times

Online Publication Date: 9 November 2007

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In intraoperative electron radiation therapy for breast cancer, attenuation plates are commonly used to protect organs at risk. These plates can be made of different materials, and the correct material (or combination of materials) has to be chosen in order to achieve the desired attenuation, while avoiding excessive backscattered radiation. The Monte Carlo method (BEAMnrcMP and DOSXYZnrcMP) has been used to characterize the electron beam generated by the setup (composed of a nondedicated linac and an applicator), and to simulate the percent depth dose (PDD) for plates of different materials. The beam has been characterized for nominal energies of 9 and 12 MeV. Several differently composed plates have been investigated: it was found, as expected, that the use of a plate presenting to the electron beam a high-Z material (i.e., lead) has to be avoided because of excessive backscatter (up to 52% compared to the PDD without plate). On the other hand, the use of a single low-Z material (i.e., aluminum) in the plate can lead to an insufficient attenuation of the beam. The two-layer plate (6 mm of Al plus 3 mm of Cu) used in S. Chiara Hospital has been found to attenuate the beam almost completely for both considered energies, causing negligible backscatter radiation. The spectrum at various depth and at the tissue-plate interface has also been investigated.
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87.53.Jw Therapeutic applications, including brachytherapy
87.56.-v Radiation therapy equipment

RADIATION THERAPY PHYSICS: Implantable MOSFET detectors: Evaluation of a new design

Tina Marie Briere, Michael T. Gillin, and A. Sam Beddar

Med. Phys. 34, 4585 (2007); http://dx.doi.org/10.1118/1.2799578 (6 pages) | Cited 4 times

Online Publication Date: 9 November 2007

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The authors have studied the performance of a new version of the implantable MOSFET detector designed for clinical use. Detectors were irradiated under 6- and 18-MV beams in water at body temperature to the calibration dose of 200 cGy/fraction for 20 daily fractions to determine their response and reproducibility. Additional measurements were performed in a solid phantom under 6-MV irradiation at room temperature to daily doses of 100, 150, 200, 250, 400 and 600 cGy/fraction. Finally, the angular dependence with respect to rotation about the detector’s longitudinal axis was studied. At body temperature, the detectors were found to have an average response within ±3% of the calibration dose with a standard deviation of 2% or less. At room temperature, doses lower than the calibration dose led to a slight overresponse while doses higher than the calibration dose led to a slight underresponse. Angular dependence was not significant, on average within 1.2% of the mean. When used as specified by the manufacturer, these detectors should provide data useful to verify the delivered dose for external beam radiation therapy within a certain tolerance.
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87.53.Bn Dosimetry/exposure assessment
85.30.Tv Field effect devices
87.56.Da Ancillary equipment
06.20.fb Standards and calibration

RADIATION THERAPY PHYSICS: Daily targeting of liver tumors: Screening patients with a mock treatment and using a combination of internal and external fiducials for image-guided respiratory-gated radiotherapy

Sunil Krishnan, Tina Marie Briere, Lei Dong, Ravi Murthy, Chaan Ng, Peter Balter, Radhe Mohan, Michael T. Gillin, and A. Sam Beddar

Med. Phys. 34, 4591 (2007); http://dx.doi.org/10.1118/1.2804578 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2007

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The feasibility and accuracy of using a mock treatment to screen suitable patients for respiratory-gated image-guided radiotherapy was investigated. Radio-opaque fiducials implanted adjacent to the liver tumor were used for online positioning to minimize the systematic error in patient positioning. The consistency in the degree of correlation between the external and internal fiducials was analyzed during a mock treatment. This technique could screen patients for gated therapy, reduce setup inaccuracy, and possibly individualize treatment margins.
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87.53.-j Effects of ionizing radiation on biological systems
87.59.bd Computed radiography
87.19.U- Hemodynamics
87.19.Wx Pneumodyamics, respiration
87.19.X- Diseases

RADIATION THERAPY PHYSICS: Characterization of optically stimulated luminescent dosimeters, OSLDs, for clinical dosimetric measurements

Paul A. Jursinic

Med. Phys. 34, 4594 (2007); http://dx.doi.org/10.1118/1.2804555 (11 pages) | Cited 41 times

Online Publication Date: 9 November 2007

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Optically stimulated luminescent dosimeters, OSLDs, are plastic disks infused with aluminum oxide doped with carbon (Al2O3:C). These disks are encased in a light-tight plastic holder. Crystals of Al2O3:C when exposed to ionizing radiation store energy that is released as luminescence (420 nm) when the OSLD is illuminated with stimulation light (540 nm). The intensity of the luminescence depends on the dose absorbed by the OSLD and the intensity of the stimulation light. OSLDs used in this work were InLight/OSL Dot dosimeters, which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). The following are dosimetric properties of the OSLD that were determined: After a single irradiation, repeated readings cause the signal to decrease by 0.05% per reading; the signal could be discharged by greater than 98% by illuminating them for more than 45 s with a 150 W tungsten-halogen light; after irradiation there was a transient signal that decayed with a 0.8 min halftime; after the transient signal decay the signal was stable for days; repeated irradiations and readings of an individual OSLD gave a signal with a coefficient of variation of 0.6%; the dose sensitivity of OSLDs from a batch of detectors has a coefficient of variation of 0.9%, response was linear with absorbed dose over a test range of 1–300 cGy; above 300 cGy a small supra-linear behavior occurs; there was no dose-per-pulse dependence over a 388-fold range; there was no dependence on radiation energy or mode for 6 and 15 MV x rays and 6–20 MeV electrons; for Ir-192 gamma rays OSLD had 6% higher sensitivity; the dose sensitivity was unchanged up to an accumulated dose of 20 Gy and thereafter decreased by 4% per 10 Gy of additional accumulated dose; dose sensitivity was not dependent on the angle of incidence of radiation; the OSLD in its light-tight case has an intrinsic buildup of 0.04 g∕cm2; dose sensitivity of the OSLD was not dependent on temperature at the time of irradiation in the range of 10–40 °C. The clinical use of OSLDs for in vivo dosimetric measurements is shown to be feasible.
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87.56.-v Radiation therapy equipment
87.57.uq Dosimetry
87.56.Da Ancillary equipment
87.53.-j Effects of ionizing radiation on biological systems

ANATOMY AND PHYSIOLOGY: Creation and establishment of a respiratory liver motion simulator for liver interventions

S. A. Müller, L. Maier-Hein, A. Mehrabi, F. Pianka, U. Rietdorf, I. Wolf, L. Grenacher, G. Richter, C. N. Gutt, J. Schmidt, H. P. Meinzer, and B. M. Schmied

Med. Phys. 34, 4605 (2007); http://dx.doi.org/10.1118/1.2805475 (4 pages) | Cited 5 times

Online Publication Date: 12 November 2007

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Image-guided surgery and navigation have resulted from convergent developments in radiology, teletransmission, and computer science and are well-established procedures in the surgical routine in orthopedic, neurosurgery, and head-and-neck surgery. In abdominal surgery, however, these tools have gained little attraction so far. The inability to transfer the methodology from orthopedic or neurosurgery is mainly a result of intraoperative organ movement and shifting. To practice and establish navigated interventions in the liver, a custom-designed respiratory liver motion simulator was built which models the human torso and is easy to recreate. To simulate breathing motion, an explanted porcine or human liver is mounted to the diaphragm model of the simulator, and a lung ventilator causes a periodic movement of the liver along the craniocaudal axis. Additionally, the liver can be connected to a circulating pump device which simulates hepatic perfusion and provides real surgical options to establish navigated interventions and simulate management of possible complications. Respiratory motion caused by the simulator was evaluated with an optical tracking system and it was shown that in vitro movement and deformation of a liver mounted to the device are similar to the liver movements in human or porcine bodies. Based on the tests, it is concluded that the novel respiratory liver motion simulator is suitable for in vitro evaluation of navigated systems and interventional and surgical procedures.
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87.80.-y Biophysical techniques (research methods)

MEDICAL PHYSICS LETTERS: The x-ray light valve: A low-cost digital radiographic imaging system

Ivaylo Koprinarov, Christie Ann Webster, Robert D. MacDougall, and J. A. Rowlands

Med. Phys. 34, 4609 (2007); http://dx.doi.org/10.1118/1.2799490 (3 pages) | Cited 2 times

Online Publication Date: 12 November 2007

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In recent years new digital x-ray radiographic and fluoroscopic systems based on large-area flat-panel technology have revolutionized our capability of producing x-ray images. However, such imagers are extraordinarily expensive and their rapid image acquisition capability is not required for many applications such as radiography. Here we report a novel approach to achieve a high-quality digital radiographic system at a cost which is only a small fraction of competitive digital technologies. The results demonstrate that our proposed x-ray light valve system has excellent spatial resolution and adequate sensitivity compared to existing technologies.
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07.85.-m X- and γ-ray instruments

RADIATION IMAGING PHYSICS: Empirical electro-optical and x-ray performance evaluation of CMOS active pixels sensor for low dose, high resolution x-ray medical imaging

C. D. Arvanitis, S. E. Bohndiek, G. Royle, A. Blue, H. X. Liang, A. Clark, M. Prydderch, R. Turchetta, and R. Speller

Med. Phys. 34, 4612 (2007); http://dx.doi.org/10.1118/1.2804744 (14 pages) | Cited 13 times

Online Publication Date: 13 November 2007

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Monolithic complementary metal oxide semiconductor (CMOS) active pixel sensors with high performance have gained attention in the last few years in many scientific and space applications. In order to evaluate the increasing capabilities of this technology, in particular where low dose high resolution x-ray medical imaging is required, critical electro-optical and physical x-ray performance evaluation was determined. The electro-optical performance includes read noise, full well capacity, interacting quantum efficiency, and pixels cross talk. The x-ray performance, including x-ray sensitivity, modulation transfer function, noise power spectrum, and detection quantum efficiency, has been evaluated in the mammographic energy range. The sensor is a 525×525 standard three transistor CMOS active pixel sensor array with more than 75% fill factor and 25×25 μm pixel pitch. Reading at 10 f∕s, it is found that the sensor has 114 electrons total additive noise, 105 electrons full well capacity with shot noise limited operation, and 34% interacting quantum efficiency at 530 nm. Two different structured CsI:Tl phosphors with thickness 95 and 115 μm, respectively, have been optically coupled via a fiber optic plate to the array resulting in two different system configurations. The sensitivity of the two different system configurations was 43 and 47 electrons per x-ray incident on the sensor. The MTF at 10% of the two different system configurations was 9.5 and 9 cycles∕mm with detective quantum efficiency of 0.45 and 0.48, respectively, close to zero frequency at ∼0.44 μC∕kg (1.72 mR) detector entrance exposure. The detector was quantum limited at low spatial frequencies and its performance was comparable with high resolution a:Si and charge coupled device based x-ray imagers. The detector also demonstrates almost an order of magnitude lower noise than active matrix flat panel imagers. The results suggest that CMOS active pixel sensors when coupled to structured CsI:Tl can be used for conventional and advanced digital mammography due to their low noise, high resolution performance.
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87.59.E- Mammography
87.63.-d Non-ionizing radiation equipment and techniques
87.63.L- Visual imaging

NUCLEAR MEDICINE PHYSICS: Joint model of motion and anatomy for PET image reconstruction

Feng Qiao, Tinsu Pan, John W. Clark, Jr., and Osama Mawlawi

Med. Phys. 34, 4626 (2007); http://dx.doi.org/10.1118/1.2804721 (14 pages) | Cited 10 times

Online Publication Date: 13 November 2007

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Anatomy-based positron emission tomography (PET) image enhancement techniques have been shown to have the potential for improving PET image quality. However, these techniques assume an accurate alignment between the anatomical and the functional images, which is not always valid when imaging the chest due to respiratory motion. In this article, we present a joint model of both motion and anatomical information by integrating a motion-incorporated PET imaging system model with an anatomy-based maximum a posteriori image reconstruction algorithm. The mismatched anatomical information due to motion can thus be effectively utilized through this joint model. A computer simulation and a phantom study were conducted to assess the efficacy of the joint model, whereby motion and anatomical information were either modeled separately or combined. The reconstructed images in each case were compared to corresponding reference images obtained using a quadratic image prior based maximum a posteriori reconstruction algorithm for quantitative accuracy. Results of these studies indicated that while modeling anatomical information or motion alone improved the PET image quantitation accuracy, a larger improvement in accuracy was achieved when using the joint model. In the computer simulation study and using similar image noise levels, the improvement in quantitation accuracy compared to the reference images was 5.3% and 19.8% when using anatomical or motion information alone, respectively, and 35.5% when using the joint model. In the phantom study, these results were 5.6%, 5.8%, and 19.8%, respectively. These results suggest that motion compensation is important in order to effectively utilize anatomical information in chest imaging using PET. The joint motion-anatomy model presented in this paper provides a promising solution to this problem.
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87.57.N- Image analysis
87.57.uk Positron emission tomography (PET)
87.57.-s Medical imaging
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