# 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

equation 5.

dR t ) Qb (t) - dK t) 5.

dt dt

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.

Q (t)

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.

CONCLUSION

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

clinically.'

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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.