Measurement system evaluates the integrated bone density over a specific cross section of bone. A digital computer converts stored bone scan data to equivalent aluminum calibration wedge thickness, and bone density is then integrated along the scan by using the trapezoidal approximation integration formula

Meharg, L. S.

English

NASA Technical Reports Server

April 1968	 Brief 68-10140 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Instrumentation for Bone Density Measurement 
Analog to TTY 
Microdensitometer H 
Scanning 	
Prea__ø_J Digital Converter F1 Digital Computer	 Input- Output 
Scan Limit 
Switches 
Bone density measurement systems with quite ac-
ceptable accuracy have been in use for some time. 
However, as increased interest in this area demands 
more and more data, the analog instrumentation used 
for data reduction lacks sufficient speed. 
The basic measurement system evaluates the inte-
grated bone density over a specific cross section of 
bone. A roentgenogram of a standard aluminum cali-
bration wedge and the bone specimen is obtained in 
a single exposure. Optical transmittance of the de-
veloped film is then measured by means of a scanning 
microdensitometer. The image of the wedge is first 
scanned to determine optical transmittance versus 
wedge thickness as recorded on the film. Graphical 
representation of the optical, scanner output for a 
scan of the wedge image is in the form of an output 
voltage curve. The bone image is scanned next along 
the desired cross section, resulting in a second output 
voltage curve. These curves are the basic inputs for 
measurement of bone density. 
The computation system must now convert the volt-
age output for the bone scan to a curve of equiva-
lent density (in terms of wedge thickness) and inte-
grate the area under the resulting curve. Conversion 
between output for the bone scan and equivalent 
wedge thickness is made using the wedge scan curve. 
The curve is entered at the value of optical scanner
output and wedge thickness is read on the abscissa. 
This equivalent wedge thickness is used in the sub-
sequent integration of the density. 
In one analog system, in use for many years, con-
version between optical scanner output during bone 
scan and equivalent wedge thickness, is made by using 
a nonlinear resistance slidewire output from a chart 
recorder. Integration is accomplished with an electro-
mechanical integrator. 
A system using a digital computer has been im-
plemented to perform the computation functions simi-
lar to those performed by the analog system. Optical 
scanner output voltage is converted to a digital format 
for storage and subsequent processing by a digital 
computer. After both wedge and bone scans have been 
completed, the computer converts stored bone scan 
data to equivalent wedge thickness by using the stored 
wedge scan data. Bone density is then integrated along 
the scan by using the trapezoidal approximation inte-
gration formula. A block diagram of the digital instru-
mentation is shown in the figure. 
In operation, data collection by the computer is 
controlled by the limit switches of the densitometer, 
which mark the beginning and end of the scans. 
Sampling times are controlled by a clock in the com-
puter. The teletype unit is used to control the com-
puter by directing it to prepare for a wedge or bone 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000140 2020-03-12T05:29:11+00:00Z
scan, specifying bone scan speed used, specifying 	 Patent status: 
printout options desired, and is also used in typing 	 No patent action is contemplated by NASA. 
identifying information on the printout.	 Source: Louis S. Meharg	 40 
Note:	 of Kaman Instruments 
Inquiries concernthg this innovation may be di- 	 under contract to 
rected to:	 Manned Spacecraft Center 
Technology Utilization Officer 	 (M SC- 11388)
Manned Spacecraft Center 
Houston, Texas 77058 
Reference: B68-10140 
Brief 68-10140	 Category 01


Instrumentation for bone density measurement

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