Search results for "phantom"
showing 10 items of 196 documents
<title>PLZT ceramics as optical phantom for simulation of light scattering in eye segments and other biological tissues</title>
1999
ABSTRACT Coefficients of light absorption ta and scattering for biological tissues lie within a broad range - minimum ones forhealthy eye tissues up to higher values (fe. t a 0.3 cm and i = 40 cm' at 633 nm for muscle tissues ) for other andmainly turbid tissues. The specific feature of the transparent PLZT ceramics (having absorption t a > 0. 1 cm in the visible and in the near infrared spectrum range) is electrically controlled light scattering. The present work reports onexperimental results of the light transport and backscattering for PLZT 9/65/35 (Pb091La009Zr065Ti035O3). We proposePLZT ceramics with fast and continuously controllable light scattering as an optical phantom for photon …
Three-dimensional mapping of the B 1 field using an optimized phase-based method: Application to hyperpolarized 3 He in lungs
2010
A novel method is presented for the three-dimensional mapping of the B1-field of a transmit radio-frequency MR coil. The method is based on the acquisition of phase images, where the effective flip angle is encoded in the phase of the nonselective hard pulse excitation. The method involves the application of a rectangular composite pulse as excitation in a three-dimensional gradient recall echo to produce measurable phase angle variation. However, such a pulse may significantly increase the radio-frequency power deposition in excess of the standard acceptable SAR limits, imposing extremely long TRs (>100 msec), which would result in acquisition times significantly greater than a single brea…
Experimentelle In-vitro-Studie zur Evaluierung eines elektronischen Detektors für die digitale Radiographie
2004
Purpose: To evaluate the contrast-detail performance of a flat-panel detector system, we performed a comparative study of this flat-panel system versus storage phosphor and conventional screen-film systems. Materials and Methods: Bone models made of human humeri were prepared with foreign bodies, fracture lines and drilled holes to create artificial fractures, osteolyses or metastases. Immersed in a water bath, hard copy images of these models were acquired with the same exposure dose (55 kV; 3.2 mAs) on the flat-panel detector, two state-of-the-art storage phosphor systems (PCR®, ADC®) and two conventional screen-film systems (Insight®, T-Mat®). Using a standardized protocol with a 4-point…
Design and characterization of a new high-dose-rate brachytherapy Valencia applicator for larger skin lesions
2016
Purpose: The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a 192Ir source; (ii) to calculate by means of the Monte Carlo(MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water. Methods: The penelope2008MC code was used to optimize dwell positions and dwell times. Next, the dose distribution in a water phantom and the leakage dose distribution arou…
Calibration of a thermoluminescent dosimeter worn over lead aprons in fluoroscopy guided procedures
2018
Fluoroscopy guided interventional procedures provide remarkable benefits to patients. However, medical staff working near the scattered radiation field may be exposed to high cumulative equivalent doses, thus requiring shielding devices such as lead aprons and thyroid collars. In this situation, it remains an acceptable practice to derive equivalent doses to the eye lenses or other unprotected soft tissues with a dosimeter placed above these protective devices. Nevertheless, the radiation backscattered by the lead shield differs from that generated during dosimeter calibration with a water phantom. In this study, a passive personal thermoluminescent dosimeter (TLD) was modelled by means of …
SU-E-I-83: Detectability Limits of a New Positron Emission Mammography in Relation to Tumour-Size, Tumour-To-Background Ratio and Activity Concentrat…
2017
Purpose:Positron emission mammography(PEM) improves spatial resolution and sensitivity, making it suitable for early breast tumours detection. The aim of this study is to evaluate the limits of a dedicated breast PET in terms of tumour‐size, tumour‐to‐background activity concentration ratio (TBR) and activity concentration. Methods: A dedicated PEM is evaluated. To characterize the device, we use a phantom of 15 cm of diameter containing 6 inserts of inner diameters 18, 15, 11, 8, 5 and 3 mm. To evaluate the detectability limits images are acquired by varying the TBR from 10 to 2 and without background activity concentration. In all the studies the activity concentration for the 6 inserts i…
Poor optical stability of molecular dyes when used as absorbers in water-based tissue-simulating phantoms
2019
Biomedical optical systems and models can be easily validated by the use of tissue-simulating phantoms. They can consist of water-based turbid media which often include inks (India ink and molecular dyes) as absorbers. Optical stability of commonly exploited inks under the influence of light, pH changes and the addition of TiO2 and surfactant, was studied. We found that the exposure to ultraviolet and visible light can crucially affect the absorption properties of molecular dyes. On average, absorption peaks decreased by 47.3% in 150 exposure hours. Furthermore, dilution can affect ink’s pH and by that, its decay rate under light exposure. When TiO2 was added to the phantoms, all molecular …
SU-E-T-530: Comparison of Analytical and Monte Carlo Calculations for Heterogeneity Corrections in LDR Prostate Brachytherapy
2013
Purpose: It is well‐known that tissue heterogeneities and calcifications have significant influence on low energy brachytherapy. The aim of this work is to study the application of a simplified analytic algorithm that could be compatible with commercial Treatment Planning System (TPS) based on TG‐43. The algorithm, based on the classic equivalent path length method, has been compared with Monte Carlo (MC) computations using Penelope2009. Methods: The analytical model scales the distance from the seed to the calculation point according to the electronic density of the medium relative to water. Then, the dose is calculated from TG‐43 consensus data (stored on a TPS) by scaling the radial dose…
A human post-mortem brain model for the standardization of multi-centre MRI studies
2015
Multi-centre MRI studies of the brain are essential for enrolling large and diverse patient cohorts, as required for the investigation of heterogeneous neurological and psychiatric diseases. However, the multi-site comparison of standard MRI data sets that are weighted with respect to tissue parameters such as the relaxation times (T1, T2) and proton density (PD) may be problematic, as signal intensities and image contrasts depend on site-specific details such as the sequences used, imaging parameters, and sensitivity profiles of the radiofrequency (RF) coils. Water or gel phantoms are frequently used for long-term and/or inter-site quality assessment. However, these phantoms hardly mimic t…
Dose determination using alanine detectors in a mixed neutron and gamma field for boron neutron capture therapy of liver malignancies
2011
IntroductionBoron Neutron Capture Therapy for liver malignancies is being investigated at the University of Mainz. One important aim is the set-up of a reliable dosimetry system. Alanine dosimeters have previously been applied for dosimetry of mixed radiation fields in antiproton therapy, and may be suitable for measurements in mixed neutron and gamma fields.Materials and MethodsTwo experiments have been carried out in the thermal column of the TRIGA Mark II reactor at the University of Mainz. Alanine dosimeters have been irradiated in a phantom and in liver tissue.ResultsFor the interpretation and prediction of the dose for each pellet, beside the results of the measurements, calculations …