Small computer assisted analysis of camera renograms Page: 4 of 13
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Where Q is the measured kidney count and Qb is the count from the
background region. Furthermore, m is the "uptake constant" and c is
a constant which corrects for systematic errors such as can occur in blood
background subtraction. This relationship is in the form for a straight
line, y = m r + c, and the constants can be determined by the technique
of least squares fitting a plot of Qk against the integral given in
equation 4. Once the constants m and C have been determined they can be used
to calculate Qk from equation 4 for the duration of the study. The uptake
activity-time curve represents the accumulation of activity that would occur
with no passage of urine. This is shown in Figures 3 and 4. Figure 3 shows
a typical background activity-time curve flagged over the aorta (see
Figure 2 for the flagged areas), and the curve of the accumulated total
counts of the background. Each data point represents the number of counts
accumulated uver 15 seconds.
One kidney at a time is analyzed using SCAAR. After curve smoothing
the background curve is multiplied by the kidney-to-background ratio
(described earlier) to obtain the curve of the activity attributed to
the background in the flagged area and then this curve is.subtracted from
the renogram curve to give a corrected renogram curve. Figure 4 a is the
uptake component of the renogram (the background integral curve which has
been corrected by the constants m and c).
Subtraction of the corrected renogram from the uptake component yields
the removal component (the accumulated total of isotope which has left
the kidney). (Figure 4). An additional calculation gives the smoothed rate
of change with respect to time of the output curve. This can be calculated
from the derivative of equation 4 or directly from the removal curve using
dR t ) Qb (t) - dK t) 5.
where R (t) is the removal component and
K (t) is the background corrected renogram curve.
THE ISOTOPE REMOVAL FACTOR
From the removal component and the extension of the uptake component,
another number, the isotope removal factor (J.RF) can be computed. This
is a measure of the efficiency with which a kidney transfers isotope out of
the kidney to the collecting system. This index is the percentage of the
uptake component at time t which is removed after a time interval A t, as
determined from the removal component. This is
IRF m R(t + t) x 100 6.
The IRF is usually calculated after a time lapse long enough to insure
that the IRF represents the actual clinical state of normal and most poorly
functioning kidneys. SCAAR calculates an average IRF between 10 and 13
minutes for delays,4 t, of 2, 3, 4, 5 and 6 minutes. The IRF is discussed
in detail by Britton and others. An additional computation gives the time
of maximum accumulation of isotope in the kidneys.
SCAAR, the program described above, has the primary advantage of
immediacy. Clinical information can be processed shortly after completion
of the clinical study. Furthermore, it is relatively easy to incorporate
new features into the program. This program is now being used regularly
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Esser, P.D.; Bradley-Moore, P.R.; Atkins, H.L.; Robertson, J.S. & Ansari, A.N. Small computer assisted analysis of camera renograms, article, January 1, 1972; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1027737/m1/4/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.