Imaging phantom

About: Imaging phantom is a research topic. Over the lifetime, 28170 publications have been published within this topic receiving 510003 citations. The topic is also known as: phantom.

Axial strain calculation using a low-pass digital differentiator in ultrasound elastography

Abstract: In ultrasound elastography, tissue axial strains are calculated from the gradient of the estimated axial displacements. However, the common differentiation operation amplifies the noises in the displacement estimation, especially at high frequencies. In this paper, a low-pass digital differentiator (LPDD) is proposed to calculate the axial strain from the estimated tissue displacement. Several LPDDs that have been well developed in the field of digital signal processing are presented. The corresponding performances are compared qualitatively and quantitatively in computer simulations and in preliminary phantom and in vitro experiments. The results are consistent with the theoretical analysis of the LPDDs.

Fast 2D phantom dosimetry for scanning proton beams

Abstract: A quality control system especially designed for dosimetry in scanning proton beams has been designed and tested. The system consists of a scintillating screen (Gd2O2S:Tb), mounted at the beam-exit side of a phantom, and observed by a low noise CCD camera with a long integration time. The purpose of the instrument is to make a fast and accurate two-dimensional image of the dose distribution at the screen position in the phantom. The linearity of the signal with the dose, the noise in the signal, the influence of the ionization density on the signal, and the influence of the field size on the signal have been investigated. The spatial resolution is 1.3 mm (1 s.d.), which is sufficiently smaller than typical penumbras in dose distributions, The measured yield depends linearly on the dose and agrees within 5% with the calculations. In the images a signal to noise ration (signal/l s.d.) of 10(2) has been found, which is in the same order of magnitude as expected from the calculations. At locations in the dose distribution possessing a strong contribution of high ionization densities (i.e., in the Bragg peak), we found some quenching of the light output, which can be described well by existing models if the beam characteristics are known. For clinically used beam characteristics such as a Spread Out Bragg peak, there is at most 8% deviation from the NACP ionization chamber measurements. The conclusion is that this instrument is a useful tool for quick and reliable quality control of proton beams. The long integration-time capabilities of the system make it worthwhile to investigate its applicability in scanning proton beams and other dynamic treatment modalities. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)02104-X].

Evaluation of right and left ventricular volume and ejection fraction using a mathematical cardiac torso phantom.

Abstract: UNLABELLED The availability of gated SPECT has increased the interest in the determination of volume and ejection fraction of the left ventricle (LV) for clinical diagnosis. However, the same indices for the right ventricle (RV) have been neglected. The objective of this investigation was to use a mathematical model of the anatomical distribution of activity in gated blood-pool imaging to evaluate the accuracy of two ventricular volume and ejection fraction determination methods. In this investigation, measurements from the RV were emphasized. METHODS The mathematical cardiac torso phantom, developed to study LV myocardium perfusion, was modified to simulate the radioactivity distribution of a 99mTc-gated blood-pool study. Twenty mathematical cardiac torso phantom models of the normal heart with different LV volumes (122.3 +/- 11.0 ml), RV volumes (174.6 +/- 22.3 ml) and stroke volumes (75.7 +/- 3.3 ml) were randomly generated to simulate variations among patients. An analytical three-dimensional projector with attenuation and system response was used to generate SPECT projection sets, after which noise was added. The projections were simulated for 128 equidistant views in a 360 degrees rotation mode. RESULTS The radius of rotation was varied between 24 and 28 cm to mimic such variation in patient acquisitions. The 180 degrees and 360 degrees projection sets were reconstructed using the filtered backprojection reconstruction algorithm with Butter-worth filtering. Comparison was made with and without application of the iterative Chang attenuation correction algorithm. Volumes were calculated using a modified threshold and edge detection method (hybrid threshold), as well as a count-based method. A simple background correction procedure was used with both methods. CONCLUSION Results indicate that cardiac functional parameters can be measured with reasonable accuracy using both methods. However, the count-based method had a larger bias than the hybrid threshold method when RV parameters were determined for 180 degrees reconstruction without attenuation correction. This bias improved after attenuation correction. The count-based method also tended to overestimate the end systolic volume slightly. An improved background correction could possibly alleviate this bias.

A 256 x 256 2-D array transducer with row-column addressing for 3-D rectilinear imaging

Abstract: We present simulation and experimental results from a 5-MHz, 256times256 2-D (65536 elements, 38.4times38.4 mm) 2-D array transducer with row-column addressing. The main benefits of this design are a reduced number of interconnects, a modified transmit/receive switching scheme with a simple diode circuit, and an ability to perform volumetric imaging of targets near the transducer with transmit beamforming in azimuth and receive beamforming in elevation. The final dimensions of the transducer were 38.4 mm times 38.4 mm times 300 mum. After a row-column transducer was prototyped, the series resonance impedance was 104 Omega at 5.4 MHz. The measured -6 dB fractional bandwidth was 53% with a center frequency of 5.3 MHz. The SNR at the transmit focus was measured to be 30 dB. At 5 MHz, the average nearest neighbor crosstalk was -25 dB. In this paper, we present 3-D images of both 5 pairs of nylon wires embedded in a clear gelatin phantom and an 8 mm diameter cylindrical anechoic cyst phantom acquired from a 256 times 256 2-D array transducer made from a 1-3 composite. We display the azimuth and elevation B-scans as well as the C-scan for each image. The cross-section of the wires is visible in the azimuth B-scan, and the long axes can be seen in the elevation B-scan and C-scans. The pair of wires with 1-mm axial separation is discernible in the elevational B-scan. When a single wire from the wire target phantom was used, the measured lateral beamwidth was 0.68 mm and 0.70 mm at 30 mm depth in transmit beamforming and receive beamforming, respectively, compared with the simulated beamwidth of 0.55 mm. The cross-section of the cyst is visible in the azimuth B-scan whereas the long axes can be seen as a rectangle in the elevation B-scan and C-scans.

Quantitative phase-contrast tomography of a liquid phantom using a conventional x-ray tube source.

Abstract: Over the last few years, differential phase-contrast x-ray computed tomography (PC-CT) using a hard x-ray grating interferometer and polychromatic x-ray tube sources has been developed. The method allows for simultaneous determination of the attenuation coefficient and the refractive index decrement distribution inside an object in three dimensions. Here we report experimental results of our investigation on the quantita-tiveness and accuracy of this method. For this study, a phantom consisting of several tubes filled with chemically well-defined liquids was built and measured in PC-CT. We find, that the measured attenuation coefficients and refractive index decrements closely match calculated, theoretical values. Moreover, the study demonstrates, how substances with similar attenuation coefficient or refractive index decrement, can be uniquely distinguished by the simultaneous, quantitative measurement of both quantities.