Method of generalized projections algorithm for image-based reduction of artifacts in radial imaging.

This work describes the method of generalized projections (MGP) as an image-based, postprocessing method to correct for phase inconsistencies caused by echo misalignments in radial imaging. Computer simulations show that MGP can correct for echo shifts, constant phase, and amplitude errors, but the accuracy of the correction is limited, and this accuracy is reduced by the addition of more degrees of freedom. In phantom experiments, MGP performed better than magnitude filtered backprojection and anti-parallel projections correction.     

Automated construction of detector models for efficiency interpolation in gamma-ray spectrometry.

A method was developed for automated construction of detector models in gamma-ray spectrometry, which can be used in Monte Carlo calculations of efficiency calibration curves. Full-energy peak efficiencies were first measured for different gamma-ray energies and for a given sample-detector arrangement and then calculated by the Monte Carlo method. For these calculations a detector model was employed along with a computer algorithm, which seeks agreement between the experimental efficiencies and the calculated ones by automatically determining the parameters of the model. The resulting agreement of the calculated data with the experimental one was within the relative uncertainty of the latter (3-4%) and the parameters of the detector models obtained were close to the values specified by the manufacturers. The detector models thus constructed can then be used for interpolation of calibration curves.     

IMPACT: image-based physiological artifacts estimation and correction technique for functional MRI.

Functional MRI (fMRI) signal variation induced by respiratory and cardiac motion affects the activation signal and limits the accuracy of analysis. Current physiological motion correction methods require either synchronization with external monitoring of respiration and heartbeat, specialized pulse sequence design, or k-space data. The IMage-based Physiological Artifacts estimation and Correction Technique (IMPACT), which is free from these constraints, is described. When images are acquired fast enough to sample physiological motion without aliasing, respiratory and cardiac signals can be directly estimated from magnitude images. Physiological artifacts are removed by reordering images according to the estimated respiratory and cardiac phases and then subtracting the Fourier-fitted variation from magnitude images. Compared with the k-space-based method, this method can efficiently and effectively reduce the overall signal fluctuation in the brain and increase the activated area. With this new technique, physiological artifacts can be reduced using traditional fMRI pulse sequences, and existing data can be corrected and reanalyzed without additional experiments.     

A dosimetric evaluation of the Eclipse AAA algorithm and Millennium 120 MLC for cranial intensity-modulated radiosurgery

The aim of this study is to assess the accuracy of a convolution-based algorithm (anisotropic analytical algorithm [AAA]) implemented in the Eclipse planning system for intensity-modulated radiosurgery (IMRS) planning of small cranial targets by using a 5-mm leaf-width multileaf collimator (MLC). Overall, 24 patient-based IMRS plans for cranial lesions of variable size (0.3 to 15.1 cc) were planned (Eclipse, AAA, version 10.0.28) using fixed field-based IMRS produced by a Varian linear accelerator equipped with a 120 MLC (5-mm width on central leaves). Plan accuracy was evaluated according to phantom-based measurements performed with radiochromic film (EBT2, ISP, Wayne, NJ). Film 2D dose distributions were performed with the FilmQA Pro software (version 2011, Ashland, OH) by using the triple-channel dosimetry method. Comparison between computed and measured 2D dose distributions was performed using the gamma method (3%/1 mm). Performance of the MLC was checked by inspection of the DynaLog files created by the linear accelerator during the delivery of each dynamic field. The absolute difference between the calculated and measured isocenter doses for all the IMRS plans was 2.5% ± 2.1%. The gamma evaluation method resulted in high average passing rates of 98.9% ± 1.4% (red channel) and 98.9% ± 1.5% (blue and green channels). DynaLog file analysis revealed a maximum root mean square error of 0.46 mm. According to our results, we conclude that the Eclipse/AAA algorithm provides accurate cranial IMRS dose distributions that may be accurately delivered by a Varian linac equipped with a Millennium 120 MLC.     

High-dose radioimmunotherapy with 90Y-ibritumomab tiuxetan: comparative dosimetric study for tailored treatment.

High-dose (90)Y-ibritumomab tiuxetan therapy and associated autologous stem cell transplantation (ASCT) were applied after dosimetry. This paper reports dosimetric findings for 3 different methods, including image corrections and actual organ mass corrections. Our first goal was to identify the most reliable and feasible dosimetric method to be adopted in high-dose therapy with (90)Y-ibritumomab tiuxetan. The second goal was to verify the safety of the prescribed activity and the best timing of stem cell reinfusion. METHODS: Twenty-two patients with refractory non-Hodgkin's lymphoma were enrolled into 3 activity groups escalating to 55.5 MBq/kg. A somewhat arbitrary cutoff of 20 Gy to organs (except red marrow) was defined as a safe limit for patient recruitment. ASCT was considered of low risk when the dose to reinfused stem cells was less than 50 mGy. (111)In-Ibritumomab tiuxetan (185 MBq) was administered for dosimetry. Blood samples were collected up to 130 h after injection to derive individual blood clearance rates and red marrow doses. Five whole-body images were acquired up to 7 d after injection. A transmission scan and a low-dose CT scan were also acquired. The conjugate-view technique was used, and images were corrected for background, scatter, and attenuation. Absorbed doses were calculated using the OLINDA/EXM software, adjusting doses for individual organ masses. The biodistribution data were analyzed for dosimetry by the conjugate-view technique using 3 methods. Method A was a patient-specific method applying background, scatter, and attenuation correction, with absorbed doses calculated using the OLINDA/EXM software and doses adjusted for individual organ masses and individually estimated blood volumes. Method B was a reference method using the organ masses of the reference man and woman phantoms. Method C was a simplified method using standard blood and red marrow volumes and no corrections. RESULTS: The medians and ranges (in parentheses) for dose estimates (mGy/MBq) according to method A were 1.7 (0.3-3.5) for lungs, 2.8 (1.8-10.6) for liver, 1.7 (0.6-3.8) for kidneys, 1.9 (0.8-5.0) for spleen, 0.8 (0.4-1.0) for red marrow, and 2.8 (1.3-4.7) for testes. None of patients had to postpone ASCT. Absorbed doses from method B differed from method A by up to 100% for liver, 80% for kidneys, 335% for spleen, and 80% for blood because of differences between standard and actual masses. Compared with method A, method C led to dose overestimates of up to 4-fold for lungs, 2-fold for liver, 5-fold for kidneys, 7-fold for spleen, 2-fold for red marrow, and 2-fold for testes. CONCLUSION: Patient-specific dosimetry with image correction and mass adjustment is recommended in high-dose (90)Y-ibritumomab tiuxetan therapy, for which liver is the dose-limiting organ. Overly simplified dosimetry may provide inaccurate information on the dose to critical organs, the recommended values of administered activity, and the timing of ASCT.     

A new adaptive interpolation algorithm for 3D ultrasound imaging with speckle reduction and edge preservation

Conventional interpolation algorithms for reconstructing freehand three-dimensional (3D) ultrasound data always contain speckle noises and artifacts. This paper describes a new algorithm for reconstructing regular voxel arrays with reduced speckles and preserved edges. To study speckle statistics properties including mean and variance in sequential B-mode images in 3D space, experiments were conducted on an ultrasound resolution phantom and real human tissues. In the volume reconstruction, the homogeneity of the neighborhood for each voxel was evaluated according to the local variance/mean of neighboring pixels. If a voxel was locating in a homogeneous region, its neighboring pixels were averaged as the interpolation output. Otherwise, the size of the voxel neighborhood was contracted and the ratio was re-calculated. If its neighborhood was deemed as an inhomogeneous region, the voxel value was calculated using an adaptive Gaussian distance weighted method with respect to the local statistics. A novel method was proposed to reconstruct volume data set with economical usage of memory. Preliminary results obtained from the phantom and a subject's forearm demonstrated that the proposed algorithm was able to well suppress speckles and preserve edges in 3D images. We expect that this study can provide a useful imaging tool for clinical applications using 3D ultrasound.     

Xenon-133, 127Xe, and 125Xe for lung function investigations: a dosimetric comparison.

Of the possible radionuclides of xenon, 127Xe and 125 Xe have better physical properties for lung function measurement than 133Xe. A comparison of the radiation doses for these three radionuclides has been made for a typical scintillation camera investigation. Using an exponential model for washin and washout of gas, it is shown that the specific activity-time relationship is always equal to the product of the spirometer concentration and the rebreathing period. It is concluded that of the three radionuclides 127Xe gives the lowest radiation dose during a typical lung function study.     

Operation and methodology of an alanine ion-selective electrode dosimetric system: II. Dose-response

Dissolution of irradiated α-alanine in an aqueous solution results in the liberation and formation of ammonia, which can be quantified for dosimetric purposes by means of an ion-selective gas sensing electrode. The operational principles, readout procedure as well as data analysis were presented and discussed in a preceding paper. Here the dose-response (0.5–1000 kGy) by direct concentration measurements is evaluated. A total ammonia yield decreasing from 6.5 (±0.3) × 10⁻⁷ mol J⁻¹ (i.e. 6.3 (±0.3) molecules per 100 eV) at 1 kGy, to 2.9 (±0.1) × 10⁻⁷ mol J⁻¹ (2.8 (±0.1) per 100 eV) at 1000 kGy is observed. No significant fading at ambient temperature is found during the first 2 months, even at 1000 kGy. Irradiation temperature coefficients of +0.34 to +0.47%°C⁻¹ were measured, dependent on dose level, The precision in concentration measurement for one calibration is within 1%; long-term precision varies from 2 to 4% (95% conf. lim.) for doses above 1 kGy.     

MRI susceptometry: image-based measurement of absolute susceptibility of MR contrast agents and human blood.

We present a novel NMR imaging technique that allows absolute determination of the magnetic susceptibility constant, chi, of a solution. By comparing the phase difference of MR images produced with an instant (echo planar) "offset" spin-echo sequence, we obtain a direct measure of the magnetic field perturbations caused by the solution. We demonstrate this method with Gd(DTPA), Dy(DTPA), human red blood cells, and superparamagnetic iron oxide particles.     

Theoretical and experimental determination of dosimetric characteristics for ADVANTAGE Pd-103 brachytherapy source.

ADVANTAGE Pd-103 brachytherapy source has been recently introduced by IsoAid for prostate permanent implants. Dosimetric characteristics (Dose rate constant, radial dose function, 2D-, and 1D-anisotropy functions) of this source model have been determined using both theoretical and experimental methods, following the updated TG-43U1 protocol. Derivation of the dose rate constant was based on recent NIST WAFAC calibration performed in accordance with the 1999 Standards. Measurements were performed in Solid Water using LiF TLD chips and the theoretical calculations were performed in Solid Water and liquid water phantom materials using PTRAN Monte Carlo code. The results of the Monte Carlo simulation have shown a dose rate constant of 0.69 cGyh(-1) U(-1) in liquid water and 0.67 cGyh(-1) U(-1) in Solid Water medium. The measured dose rate constant in Solid Water was found to be 0.68+/-8% cGyh(-1) U(-1), which is in a good agreement (within +/-5%) to the Monte Carlo simulated data. The 2D- and 1D-anisotropy functions of the ADVANTAGE Pd-103 source were calculated for radial distances ranging from 0.5 to 5.0 cm. Radial dose function was determined for radial distances ranging from 0.2 to 8.0 cm using line source approximation. All these calculations are based on L(eff) equal to 3.61 cm, calculated following TG-43U1 recommendations. The tabulated data for 2D-anisotropy function, 1D-anisotropy function, dose rate constant and radial dose function have been produced for clinical application of this source model.     

A phantom for dosimetric characterization of small radiation fields: design and use

An acrylic phantom was designed and constructed for the acquisition and verification of basic dosimetric data of narrow fields in stereotactic radiotherapy/radiosurgery (SRT/SRS) using thermoluminescent (TL) dosimetry. An array of holes to accommodate up to 426 dosimeters was used to allow the assessment of dose distribution in circular fields with a 1-mm spatial dose resolution with minimal field perturbation. It was found experimentally that there must be a minimum gap of 1 mm between neighboring dosimeters in 6-MV photon fields. Most of the dosimetric characteristics of a 6-MV x-ray SRS/SRT unit assessed using TL dosimetry and ion chamber dosimetry were in good agreement when the longitudinal axis of the chamber was parallel to the central beam axis. TL dosimetry showed that the penumbra width increased with increasing collimator aperture. The low cost of the phantom and the widespread use and familiarity of TL dosimetry in radiotherapy departments offer a significant advantage in the use of the proposed methodology.     

A review on strength exercise-induced muscle damage: applications, adaptation mechanisms and limitations

This study aims to review the main aspects that induce muscle damage, and to discuss the adaptations of this phenomenon, applications and limitations of this study area. Damage induced by strength training has been utilized for two purposes: 1) verification of the recovery period required between training sessions, which has a direct influence on designing exercise programs; and 2) as indication for higher training intensity, mainly in studies on the "repeated bout effect". There is some speculation about the role of muscle damage in inducing hypertrophy. However, studies demonstrate that exercise-induced muscle damage may not be a consistent indicator of higher chronic hypertrophic response, because hypertrophy also occurs in training strategies with very low mechanical overloads. In addition, aerobic exercise, also induces muscle damage, exhibits no hypertrophic response after training. The remodeling process induced bay muscle damage promotes alterations to strength x length relationship for stretched positions, indicating an increased number of sarcomeres in series, due to strength exercises. Therefore, the study on strength exercise-induced damage seems to be adequate for implementing adequate rest periods to recovery from different sessions of strength training, and not to suggest chronic hypertrophy.     

Radioiodine-131 therapy for well-differentiated thyroid cancer--a quantitative radiation dosimetric approach: outcome and validation in 85 patients.

For almost five decades, 131I treatment of thyroid cancer has been based empirically on administered activity rather than on actual radiation doses delivered. In 1983, we defined radiation dose thresholds for successful treatment. This report is concerned with the subsequent validation of those thresholds in 85 patients. The successful ablation of thyroid remnants occurred after a single initial 131I administration in 84% of inpatients and in 79% of outpatients when treatment was standardized to a radiation dose of at least 30,000 cGy (rad). Administered activities low enough to permit outpatient therapy could be used in 47% of the patients. Lymph node metastases were treated successfully in 74% of patients with a single administration of 131I calculated to deliver at least 8,500 cGy (rad). For athyrotic patients with nodal metastases only, success was achieved in 86% of patients at tumor doses of at least 14,000 cGy (rad). These success rates are equal to or better than those reported with empiric methods of 131I administration. The individualized treatment planning selectively allocates hospitalization and higher exposures to 131I to those patients who require them.     

An iodine-125 plaque for radiotherapy of the eye: manufacture and dosimetric considerations

A comparison of computer dose calculations and thermoluminescent dosemeter measurements in a phantom is given for an iodine-125 plaque for radiotherapy of the eye. The off-central-axis measurements and their relationship to the central-axis depth doses are documented. It was found that the gold backing of the applicator did not influence dosimetry in the phantom and thus the eye.