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A Penetrameter Method for Field kV Calibration of Diagnostic X-Ray Machines

A Penetrameter Method for Field kV Calibration of Diagnostic X-Ray Machines A Penetrameter Method for Field kV Calibration of Diagnostic X-Ray Machines 1 Leonard Stanton , M.S. 2 , David A. Lightfoot , M.A. 3 and Steven Mann 4 230 North Broad Street Philadelphia, Penna. 19102 ↵ 2 Associate Professor of Radiology (Radiologic Physics), Hahnemann Medical College; Consultant Physicist, Lankenau Hospital, Philadelphia, Penna. ↵ 3 Senior Instructor in Radiology (Radiologic Physics), Hahnemann Medical College. Excerpt Low-kilovoltage studies are useful for detection of objects which normally exhibit low radiographic contrast. For example, in mammography low kilovoltage and inherent filtration permit detection of punctate calcifications and fine soft-tissue structures in fat. Since diagnostic machines are designed primarily for use in the 50 to 150 kV range, their dial calibrations are usually in error at low settings. As an instance, dial settings of 27 pkV typically yield measured values of about 32, and occasionally up to 40 pkV. The problem is complicated by the fact that both contrast and film density depend critically on kilovoltage in this range. While knowledge of the calibration is most important in low-kilovoltage work, it is also useful in more conventional radiography, where it is often convenient to match technics in different x-ray rooms of the same or even different departments. For this reason, we have designed penetrameters for both low kilovoltage and conventional work. Table I summarizes five other frequently used kilovoltage-measurement methods. The absolute and spark-gap methods are the oldest and yield good results in the laboratory. In both, calibration under tube load requires cable adapters, and some shock hazard is present. Absolute measurements involve voltage dividers used with precision cathode-ray oscilloscopes; both must be accurately calibrated to assure meaningful results. Measurements with spark gaps must be properly corrected for several variables, and the points or spheres be relatively free from surface defects. Also, significant errors are produced by contactor transient voltage surges. Neither method is convenient for field use because bulky equipment is required. The second two methods infer the kilovoltage from x-ray measurements, so shock hazard is avoided. The fluorescence method is based on two facts. First, the highest photon energy in an x-ray beam, in keV, is numerically the same as the operating pkV. Second, K-orbit fluorescence of an element cannot occur until a threshold photon energy is exceeded. Hence, by using a set of several different K-orbit fluorescent materials, one can calibrate the machine dial at their corresponding peak-kilovolt locations. The Newell-Henny procedure specifies the peak kilovoltage from the slope of the x-ray transmission curve of a heavily filtered beam. Both these methods as presently employed require a fairly exacting and heavy setup for reasonable accuracy. In addition, a full dial kilovolt calibration is time-consuming and may tie up the machine for several hours, particularly at low kilovoltages. The simple step-wedge technic is included primarily out of respect to tradition. It is convenient and usefully employed empirically by many, but is inherently only qualitative, for reasons of mAs, filtration, development, and other variables. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiology Radiological Society of North America, Inc.

A Penetrameter Method for Field kV Calibration of Diagnostic X-Ray Machines

Stanton, Leonard; Lightfoot, David A.; Mann, Steven
Radiology , Volume 87 (1): 87 – Jul 1, 1966
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Publisher
Radiological Society of North America, Inc.
Copyright
Copyright © 1966 by Radiological Society of North America
ISSN
1527-1315
eISSN
0033-8419
DOI
10.1148/87.1.87
pmid
5940480
Publisher site
See Article on Publisher Site

Abstract

A Penetrameter Method for Field kV Calibration of Diagnostic X-Ray Machines 1 Leonard Stanton , M.S. 2 , David A. Lightfoot , M.A. 3 and Steven Mann 4 230 North Broad Street Philadelphia, Penna. 19102 ↵ 2 Associate Professor of Radiology (Radiologic Physics), Hahnemann Medical College; Consultant Physicist, Lankenau Hospital, Philadelphia, Penna. ↵ 3 Senior Instructor in Radiology (Radiologic Physics), Hahnemann Medical College. Excerpt Low-kilovoltage studies are useful for detection of objects which normally exhibit low radiographic contrast. For example, in mammography low kilovoltage and inherent filtration permit detection of punctate calcifications and fine soft-tissue structures in fat. Since diagnostic machines are designed primarily for use in the 50 to 150 kV range, their dial calibrations are usually in error at low settings. As an instance, dial settings of 27 pkV typically yield measured values of about 32, and occasionally up to 40 pkV. The problem is complicated by the fact that both contrast and film density depend critically on kilovoltage in this range. While knowledge of the calibration is most important in low-kilovoltage work, it is also useful in more conventional radiography, where it is often convenient to match technics in different x-ray rooms of the same or even different departments. For this reason, we have designed penetrameters for both low kilovoltage and conventional work. Table I summarizes five other frequently used kilovoltage-measurement methods. The absolute and spark-gap methods are the oldest and yield good results in the laboratory. In both, calibration under tube load requires cable adapters, and some shock hazard is present. Absolute measurements involve voltage dividers used with precision cathode-ray oscilloscopes; both must be accurately calibrated to assure meaningful results. Measurements with spark gaps must be properly corrected for several variables, and the points or spheres be relatively free from surface defects. Also, significant errors are produced by contactor transient voltage surges. Neither method is convenient for field use because bulky equipment is required. The second two methods infer the kilovoltage from x-ray measurements, so shock hazard is avoided. The fluorescence method is based on two facts. First, the highest photon energy in an x-ray beam, in keV, is numerically the same as the operating pkV. Second, K-orbit fluorescence of an element cannot occur until a threshold photon energy is exceeded. Hence, by using a set of several different K-orbit fluorescent materials, one can calibrate the machine dial at their corresponding peak-kilovolt locations. The Newell-Henny procedure specifies the peak kilovoltage from the slope of the x-ray transmission curve of a heavily filtered beam. Both these methods as presently employed require a fairly exacting and heavy setup for reasonable accuracy. In addition, a full dial kilovolt calibration is time-consuming and may tie up the machine for several hours, particularly at low kilovoltages. The simple step-wedge technic is included primarily out of respect to tradition. It is convenient and usefully employed empirically by many, but is inherently only qualitative, for reasons of mAs, filtration, development, and other variables.

Journal

Radiology – Radiological Society of North America, Inc.

Published: Jul 1, 1966

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