Mammography Beam Research Articles

Garfield++ simulation of a TH-GEM based detector for standard mammography beam dosimetry

The TH-GEM based detector is a robust, simple to manufacture, high-gain gaseous electron multiplier. Its operation is based on a standard printed circuit board (PCB) coated on both sides by metallic material, perforated in a millimeter pattern, and immersed in gas. In order to study the feasibility of using TH-GEM type detectors in dosimetric applications for standard mammography beams, a prototype with adequate dimensions and materials was produced. The present work encompasses the calculations of electric fields by the Gmsh and Elmer software packages and the avalanche simulation using Garfield++ library of a TH-GEM detector filled with Ar/CO2 mixture at atmospheric pressure.

Validation of kVp measurement using the HVL approach for standard beam qualities for mammography

In mammography imaging, the most common target material used in mammography machines are Molybdenum (Mo) target with Mo filters. In the publication of International Electrotechnical Commission (IEC) 61267, the establishment of mammography beam qualities assembly are given in 3 fixed parameters namely the target material which is Mo, the Mo filter thickness and the tube voltage. While, Mo target with rhodium (Rh) filters combination standard beam qualities were established by the Physikalish-Technische Bundesanstalt (PTB) primary standard Laboratory. The objective of this study is to measure the kVp and HVL ranging from 23-31 kV. Later compare the displayed kilovoltage peak (kVp) on the control panel with the kVp measured using a non-invasive kVp meter and validating them with the HVL measurement. From the results, the kVp dialed and kVp measured shows significant difference by 2-4 kV. The HVL measured for the kVp before and after corrected also shows similar pattern, where the HVL after kVp is correct is almost identical to the standard beam qualities with the difference of 1%. This verifies that the kVp measurement using a non-invasive kVp meter can be validated with just a simple measurement of its HVL for mammography standard beam qualities.

Comparison of air kerma measurements for tungsten anode based mammography x-ray beam qualities (EURAMET.RI(I)-S4.1)

A comparison of the air kerma standards for x-radiation qualities used in mammography was performed between the PTB and the IAEA. Two reference-class ionization chamber types Radcal RC6M and Magna A650 of the IAEA and tungsten anode based beam qualities with Mo and Al external filtrations (W+Mo, W+Al) established at both laboratories were selected for the comparison. The calibration coefficients, N K_air, were determined for the transfer chambers at the PTB in May 2015 and before and after this at the IAEA Dosimetry Laboratory. The results show good agreement, to be well within the 0.55 % standard uncertainty of the comparison. Correction factors to determine N K_air for these beam qualities based on calibration in RQR-M mammography beam qualities, established according to the IEC 61267 standard, were also calculated for the Radcal RC6M, 10X5-6M, and Magna A650 types of chambers.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Transferring calibration coefficients from ionisation chambers used for diagnostic radiology to transmission chambers

In this work, the response of a double volume transmission ionisation chamber, developed at the Instituto de Pesquisas Energéticas e Nucleares, was compared to that of a commercial transmission chamber. Both ionisation chambers were tested in different X-ray beam qualities using secondary standard ionisation chambers as reference dosimeters. These standard ionisation chambers were a parallel-plate and a cylindrical ionisation chambers, used for diagnostic radiology and mammography beam qualities, respectively. The response of both transmission chambers was compared to that of the secondary standard chambers to obtain coefficients of equivalence. These coefficients allow the transmission chambers to be used as reference equipment.

Imaging performance of the hybrid pixel detectors XPAD3-S

Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard ‘International Electrotechnical Commission’ (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures (∼0.1–400 µGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than ∼5000 photons has been found, corresponding to exposures above ∼110 µGy and ∼50 µGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses (∼3, 30 and 300 µGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of ∼1, thanks to its high efficiency (∼100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is ∼0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.

Performance of a high fill factor, indirect detection prototype flat‐panel imager for mammography

Empirical and theoretical investigations of the performance of a small-area, high-spatial-resolution, active matrix flat-panel imager, operated under mammographic conditions, is reported. The imager is based on an indirect detection array incorporating a continuous photodiode design, as opposed to the discrete photodiode design employed in conventional flat-panel imagers. Continuous photodiodes offer the prospect of higher fill factors, particularly for arrays with pixel pitches below approximately 100 microm. The array has a pixel-to-pixel pitch of 75 microm and a pixel format of 512 x 512, resulting in an active area of approximately 3.8 x 3.8 cm2. The array was coupled to two commercially available, structured CsI: Tl scintillators of approximately 150 microm thickness: one optimized for high light output (FOS-HL) and the other for high spatial resolution (FOS-HR), resulting in a pair of imager configurations. Measurements of sensitivity, modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) were performed with a 26 kVp mammography beam at exposures ranging from approximately 0.5 to approximately 19 mR. MTF results from both CsI:Tl scintillators show that the array demonstrates good spatial resolution, indicating effective isolation between adjacent pixels. The effect of additive noise of the system on DQE was observed to be significantly higher for the FOS-HR scintillator compared to the FOS-HL scintillator due to lower sensitivity of the former. For the FOS-HL scintillator, DQE performance was generally high at high exposures, limited by the x-ray quantum efficiency, Swank factor and the MTF of the scintillators. For both scintillators, the DQE performance degrades at lower exposures due to the relatively large contribution of additive noise. Theoretical calculations based on a cascaded systems model were found to be in general agreement with the empirically determined NPS and DQE values. Finally, such calculations were used to predict potential DQE performance for hypothetical 50 microm pixel pitch imagers, employing similar continuous photodiode design and realistic inputs derived from the empirical measurements.

A simple device to assist in needle positioning procedures.

At breast biopsy, use of a simple disk that fits into the hub of the needle can facilitate accurate placement of the needle with conventional lesion localization techniques. This disk forms a surface onto which the shadows of the localization crosshairs project so that the operator can advance the needle and maintain its alignment in the direction of the mammography beam by using the field light. The insert has been used successfully in more than 100 procedures.

Shielding requirements for mammography.

Shielding requirements for mammography installations have been investigated. To apply the methodologies of NCRP Report No. 49, the scatter-to-incident ratio of a typical mammography beam was measured, and the broad beam transmission was calculated for several representative beam spectra. These calculations were found to compare favorably with published low kVp tungsten-targeted x-ray transmission through a variety of shielding materials. Radiation shielding tables were developed from the calculated transmissions through Pb, concrete, gypsum, steel, plate glass, and water, using a technique which eliminates the "add one HVL" rule. It is concluded that Mo-targeted x-ray beams operated at 35 kVp require half the shielding of W-targeted beams operated at 50 kVp, and that adequate, cost-effective shielding calculations will consider alternatives to Pb.

Comparison of ion chamber and TLD dosimetry in mammography.

An ionization chamber method has been developed to measure exposure vs depth in a uniform BR 12 "average breast" phantom. It employs a Memorial mammography chamber for exit exposure measurements; resulting data is then corrected for backscatter as well as for the exceptionally thin window of this chamber. A careful comparison has then been made with relative exposure vs depth curves obtained using TLD at several mammography beam qualities, for identical exposure factors and SSD values. Use of a correction for residual and background TL signals significantly improved agreement between TLD and ion chamber curves in the 28 to 35 kVp/0.03 mm Mo range of beam quality. Agreement was within +/- 5% for the Mo target tube, but TLD readings were 4%--8% higher than ion chamber values for the W/Mo target tube. At Xeromammography energies (45 kVp/1.6 mm Al), corrected TLD curve readings were 6% higher at depth than ion chamber curve values. TLD meaurements with 28 to 35 kVp/0.03 mm Mo beams tend to underestimate dosage to the midbreast parenchyma. For example, in a 5 cm "average breast", the underestimation ranges from 2%--10% for corrected, 10%--16% for uncorrected TLD readings.

Xeromammographic cone edge pressure to shift deep lesions into view: a simple modification and technique.

A straight lower edge on the flat side of an open-ended mammographic cone, applied firmly downward along the chest wall, may sometimes displace deepseated breast lesions into the mammography beam. This can be done with simple materials.