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Medical X-Ray Tube Spectra for Mammography and Radiology

molybdenum spectrum
Figure 1. X-Ray Tube Monitor for Mammography Machines

W Spectrum
Figure 2. X-Ray Tube Monitor for Radiology Machines

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

Features

  • Direct Measurement Spectra
  • End Point Energy (kVp)
  • See what the patient gets:
    • NO Compton Spectra
    • Escape Peak Adjustment with XRF-FP Software
  • 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
  • No Liquid Nitrogen

Design Objective

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

Significance of the Measurement

Complete System Includes:

Option 1 (recommended)

  • Detector - XR-100T-CdTe
  • Digital Pulse Processor, MCA, and Power Supply - PX4
  • Collimator Kit - EXVC
  • Escape Peak Adjustment Software - XRF-FP

Option 2

 xr100t-cdte x-ray and gamma ray detector photo
Figure 3. XR-100T-CdTe with PX4.
All Solid State Design - - - No Liquid Nitrogen!!!

System Description

The XR-100T-CdTe is a high performance X-Ray and Gamma Ray detector mounted on a thermo-electric cooler (Peltier type) together with the input FET to the preamplifier. Monitored by an integrated circuit, these components are kept at -30° C and are enclosed in a hermetic package with a vacuum tight, light tight Beryllium window. Power and signal processing to the detector is provided by either the PX4 or the PX2T-CdTe. Both ensure quick, stable operation in less than one minute from power turn-on. The PX4 is a power supply, digital pulse processor, and MCA. It connects via USB to a PC. The PX2T-CdTe must be connected to the input of the Multichannel Analyzer like the Amptek MCA8000A "Pocket MCA."

Collimator Kit

Amptek has developed the EXVC Collimator Kit to collimate the primary X-ray beam. This system is comprised of the standard 1.5 inch extender box which slides inside a Collimator Housing. 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.

exvc collimator kit for the xr100 detector
Figure 4. EXVC Collimator Kit.


Figure 5. XR-100T-CdTe with the EXVC and PX4.

The kit includes

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 XRF-FP Software

The XRF-FP sofware 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.

80 kev tungsten tube output spectrum
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.

Application Notes

References

  1. A. Karellas, et al. "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.

Medical X-Ray Detector Specifications and description in PDF format (43 k)

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Revised April 22, 2008