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Medical X-Ray Detector for Mammography and Radiology

This detector system was designed to simultaneously measure the X-Ray tube peak potential (kVp), and to characterize the mammographic X-Ray tube spectrum.

Features

  • Direct Measurement Spectra
  • End Point Energy (kVp)
  • See what the patient gets:
  • Self-Calibrating System
  • Look straight at the X-Ray tube and record simultaneously both the spectrum and the peak potential (kVp)
  • The technology that went to Mars on the Pathfinder Mission is now available to Radiology!
  • A must detector for every Radiology Department
  • For Quality Assurance in Radiographic and Fluoroscopic Systems

Equipment needed

Figure 1. EXVC Collimator Kit on the X-123CdTe

Design Objective

This detector system was designed to simultaneously measure the X-Ray tube peak potential (kVp), and to characterize the mammographic X-Ray tube spectrum.

Significance of the Measurement

  • Both the tube spectrum and the peak potential (kVp) are important parameters affecting the image quality in film-screen and digital mammography.
  • Automatic selection of proper target/filter combination in modern mammography systems may be affected by improper kVp.
  • In conventional devices, the user depends on central laboratory calibration and has no easy way to calibrate the instrument during use.

Complete System Includes:

  • Detector – X-123CdTe
  • Collimator Kit – EXVC
  • Escape Peak Adjustment Software – XRS-FP

Example Output Spectra


Figure 2. X-Ray Tube Monitor for Mammography Machines


Figure 3. X-Ray Tube Monitor for Radiology Machines

Above Spectra Courtesy of Dr. Andrew Karellas Ph.D, University of Massachusetts Medical School, Worcester, MA. 01655 USA

Figure 4. Direct output x-ray spectra from the Mini-X x-ray tube (Ag target – top, W target – bottom).

System Description

X-123CdTe

Amptek’s specialty is X-ray and gamma-ray spectrometers, which are small, low power, high performance, and simple to operate. The X-123CdTe combines in a single package Amptek’s standard, high performance X-ray spectroscopy components: the XR-100CdTe detector and preamplifier, DP5 digital pulse processor and MCA, and PC5 power supply. The result is a complete integrated system which can fit in your hand. In many commercially available systems, the preamplifier alone has more size, mass, and power than this integrated system. It requires only 2 connections to run: +5 VDC power and a standard RS-232, USB, or Ethernet connection. With the X-123CdTe, anyone can rapidly obtain high quality X-ray and gamma-ray spectra.

Collimator Kit

Amptek has developed the EXVC Collimator Kit to collimate the primary X-ray beam. The Collimator Housing can accommodate up to two Tungsten collimator disks that are placed inside a bayonet holder in front of the detector. By selecting the appropriate Tungsten collimator disks, the user can reduce the incoming X-ray flux and allow the detector and electronics to process the X-ray spectrum. Seven different Tungsten collimator disks are provided with different size holes (ranging from 25 µm to 2,000 µm hole) in order to allow for a wide range of applications. The Collimator Housing is made out of stainless steel.

Figure 5. EXVC Collimator Kit. It can slide over the 1.5 inch extender of the X-123.

The kit includes
  • Stainless steel collimator housing
  • Tripod and mounting plate
  • Laser pointer
  • Brass Spacer
  • 5 Tungsten (W) Collimator disks:
    • 1 mm thick with 25 µm hole
    • 1 mm thick with 50 µm hole
    • 2 mm thick with 400 µm hole
    • 2 mm thick with 1000 µm hole
    • 2 mm thick with 2000 µm hole

All Tungsten disks are made of alloy HD17 (90% W, 6% Ni, 4% Cu).

All Tungsten disks and spacers have a diameter of 0.625 inches.

Optional: EXVC-W-SPACER
This Tungsten (W) Spacer /Collimator is 36 mm thick with a 300 µm hole. It is designed to stop and collimate x-rays greater than 100 keV produced from high energy tubes.

Escape Peak Adjustment with XRS-FP Software

The XRS-FP software can be used to adjust the output spectrum for the escape peaks of the CdTe detector. This can be a significant effect for higher energy x-ray tubes that operate above the absorption edges of Cd and Te.

For more information please see the application note ANCDTE1: CdTe Measurement of X-Ray Tube Spectra: Escape Events.


Figure 6. Plot showing a tungsten (W) x-ray tube output spectrum taken with a CdTe detector after processing to remove escape events. The gray trace shows the original spectrum. The green trace illustrates the escape events in the original spectrum. These are subtracted from this original spectrum, then the correct energies are computed (by adding in the energy which escaped). The blue trace shows the corrected escape events, which are then summed with the gray trace. The dark black trace shows the final result of the processing with the events in their correct channels.

References

  1. A. Karellas, I. Sechopoulos, I. Levis, A. C. Huber, and J. A. Pantazis, “Measurement of the x-ray spectra and tube potential in mammographic units with a self-calibrating compact cadmium zinc telluride (CZT) detector,” Radiology 205(P), 301 (1997).
  2. Matsumoto, Massao, et al. “Direct measurement of mammographic x-ray spectra using CdZnTe detector,” Medical Physics 27 (7), July 2000. p. 1490.
  3. Vedantham, Srinivasan, et al. “Mammographic imaging with a small CCD-based digital cassette: Physical characteristics of a clinical system,” Medical Physics 27 (8), August 2000, p. 1832.
  4. Vedantham, Srinivasan, et al. “Full breast digital mammography with an amorphous silicon-based flat panel detector: Physical characteristics of a clinical prototype,” Medical Physics 27 (3), March 2000, p. 558.
  5. S. Miyajima, “Thin CdTe detector in diagnostic x-ray spectroscopy,” Medical Physics, Vol. 30 No. 5, May 2003.
  6. S. Miyajima, K. Imagawa, M. Matsumoto, “An alignment method for mammographic X-ray spectroscopy under clinical conditions,” The British Journal of Radiology, 75 (2002), 763-766. © 2002 The British Institute of Radiology
    Abstract: This paper describes an alignment method for mammographic X-ray spectroscopy under clinical conditions. A pinhole, a fluorescent screen, a laser device and the case for a detector are used for alignment of the focal spot, a collimator and a detector. The method determines the line between the focal spot and the point of interest in an X-ray field radiographically. The method allows alignment for both central axis and off-axis directions.
  7. S. Aiello, et al. “FLUXEN portable equipment for direct X-ray spectra measurements,” Nuclear Instruments & Methods in Physics Research, A 518 (2004) 389-390.
  8. P. Baldelli, et al. “Development of a quasi-monochromatic source for mammography applications,” Nuclear Instruments & Methods in Physics Research, A 518 (2004) 386-388.
  9. S. Miyajima and K. Imagawa, “CdZnTe detector in mammographic x-ray spectroscopy,” Physics in Medicine and Biology, 47 (2002) 3959-3972.
  10. S. Stumbo, U. Bottigli, B. Golosio, and P. Oliva, “Direct analysis of molybdenum target generated x-ray spectra with a portable device,” Med. Phys. 31 (10), p. 2763-2770, October 2004.
    Abstract: In routine applications, information about the photon flux of x-ray tubes is obtained from exposure measurements and cataloged spectra. This approach relies mainly on the assumption that the real spectrum is correctly approximated by the cataloged one, once the main characteristics of the tube such as voltage, target material, anode angle, and filters are taken account of. In practice, all this information is not always available. Moreover, x-ray tubes with the same characteristics may have different spectra. We describe an apparatus that should be useful for quality control in hospitals and for characterizing new radiographic systems. The apparatus analyzes the spectrum generated by an x-ray mammographic unit. It is based on a commercial CZT produced by AMPTEK Inc. and a set of tungsten collimator disks. The electronics of the CZT are modified so as to obtain a faster response. The signal is digitized using an analog to digital converter with a sampling frequency of up to 20 MHz. The whole signal produced by the x-ray tube is acquired and analyzed off-line in order to accurately recognize pile-up events and reconstruct the emitted spectrum. The energy resolution has been determined using a calibrated x-ray source. Spectra were validated by comparison of the HVL measured using an ionization chamber. © 2004 American Association of Physicists in Medicine.
  11. K. Maeda, M Matsumoto, A. Taniguchi, “Compton-scattering measurement of diagnostic x-ray spectrum using high-resolution Schottky CdTe detector,” Med. Phys. 32 (6), p. 1542-1547, June 2005. Available online.
  12. U. Bottigli, B. Golosio, G. L. Masala, P. Oliva, S. Stumbo, P Delogu, M. E. Fantacci, L. Abbene, F. Fauci, G. Raso, “Comparison of two portable solid state detectors with and improved collimation and alignment device for mammographic x-ray spectroscopy,”Med. Phys. 33 (9), p.3469-3477, September 2006. Available online.
  13. L. Abbene et al., “X-ray spectroscopy and dosimetry with a portable CdTe device,” Nuclear Instruments and Methods in Physics Research A 571 (2007) p. 373-377.
  14. G. Gerardi et al., “Digital filtering and analysis for semiconductor X-ray detector data acquisition,” Nuclear Instruments and Methods in Physics Research A 571 (2007) p. 378-380.
  15. Miceli, A., Thierry, R. et al.,”Comparison of simulated and measured spectra of an industrial 450 kV X-ray tube,” Nuclear Instruments and Methods in Physics Research A, 580 (2007) p.123-126.
  16. Josilene C. Santos, Alessandra Tomal, Tânia A. Furquim, Agnes M. F. Fausto, Maria S. Nogueira, Paulo R. Costa, “Direct measurement of clinical mammographic x-ray spectra using a CdTe spectrometer,” Medical Physics, 26 May 2017.  Available online.