VOL. ii8, No. MEAUREMENT OF THYRODAL TECHNETUM UPTAKE WTH THE GAMMA CAMERA AND COMPUTER YTEM* Downloaded from www.ajronline.org by 46.3.26.89 on 3/8/18 from P address 46.3.26.89. Copyright ARR. For personal use only; all rights reserved By HAROLD L. ATKN and JOHANNE F. KLOPPER T HE determination of the uptake of technetium 99111 as pertechnetate by the thyroid provides a measurement of the trapping ability of the gland. t is also a useful guide to the over-all function of the gland as an indicator of the clinical state of the patient. The determination of the pencentage of an administered dose which is in the gland is more complicated for Tc9Om than it is for radioiodine for a number of reasons: (i) the amount in the gland at any time is a small percentage of the administered dose; (2) the circulating activity is relatively high; (3) nearby salivary glands concentrate technetium to a level similar to the thyroid; and () the time at which the radionuclide is concentrated to a maimum degree in the gland is highly variable. Previously described methods have generally used a rectilinear scanner with a dot counting method and made a comparison with a standard.2 9 Tracings of count rate versus time have also been utilized. Briefly described in abstracts, but never fully published, are kinetic studies, one of which uses a gamma camera and a multichannel analyzer system for this purpose.3 4 7 A computer-gamma camera system has also been described. ome authors have indicated a preference for the gamma camera over the rectilinear scanner for thyroid imaging. Our own eperience in comparing the 2 methods of imaging have led us also to this conclusion. Therefore, we have adapted our method to the gamma camera following the acquisition of a computer multichannel analyzer system interfaced to the camera. METHOD UPTON, LONG LAND, NEW YORK All doses of Tc99m pertechnetate (approimately 2.5 mc) are measured out at the same time prior to the day s clinical activities. These are compared in an ionization chamber dose-calibrator so that the maimum variation in activity is 5 pen cent on less. One dose is diluted to ioo ml., after which 3 ml. (3 per cent) is put into a thyroid phantom containing 2 ml. water. The thyroid phantom is inserted into an AEA neck phantom and serves as a 3 pen cent standard. A flood field image from a planar source of radioactivity is recorded by the gamma camera through the pin-hole collimator and stored on magnetic tape. This image can then be used to connect subsequent images obtained by the pin-hole collimator for nonlinearity of camera response through use of a computer program. A 3 minute recording of the standard is obtained at a distance from the pin-hole to the anterior surface of the phantom of 2 cm. This is also stoned on tape and the time of recording is noted. The patient is placed supine under the gamma camera and positioned so that the anterior surface of the neck over the thyroid region is 2 cm. from the pin-hole. Following intravenous injection of the technetium, sequential i minute scintiphotos are obtained over the net 3 mmutes and stored on tape. The data are played back following cornpletion of all clinical studies. The frame containing the standard image is recalled, connected for field distortion by the cornputer, and the counts from the thyroid phantom totalized. For each patient the thyroid region is flagged by setting cursors to include the thyroid image and a dynamic read of * From the Medical Department, Brookhaven National Laboratory, Upton, Long sland, New York. 831
832 Harold L. Atkins and johannes F. Kloppcr.\ (;t -, 1j73 Downloaded from www.ajronline.org by 46.3.26.89 on 3/8/18 from P address 46.3.26.89. Copyright ARR. For personal use only; all rights reserved COtlllts veirus time for each minute intervat is displayed. lle time when tile maimum concentration of radioactivity ill the thyroid is obtained is noted. Three frames representing 3 minutes of recording time are combined, displayed and corrected for field response. The counts over a region which completely enconipasses the thyroid but ecludes tile salivary glands are determined. The counts over a background region just below the thyroid are determined and, after correction for differences in total area, are sul)tracted from the coults oh-. tamed over the thyroid region to give net thyroid counts (Fig. i, d and B). Tile standard counts are corrected for decay to tile time at which the maimum uptake of technetium ilas occurred. Then dividing net thyroid counts by the 3 per cent standard an(l multiplying l)v 3 gives the per cent administered dose in the thyroid. Following tile uptake study the pin-hole is brought t( ) 6 cm. from the neck and another image obtained with co-ioo, counts for anatomic detail. REULT AND )CUON lle choice of a 2 cm. distance from pin- r 24-8 2 DTANCE N CENTMETER c;. 2. hect of distance from pin-hole collimator on count -ate ()Ve- the di vroid plian toni. FG.. (A and B) Computer oscilloscope display of neck image with thyroid region intensified.
VOL. 1i8, No. Thynoidal Technetium Uptake 833 Downloaded from www.ajronline.org by 46.3.26.89 on 3/8/18 from P address 46.3.26.89. Copyright ARR. For personal use only; all rights reserved hole aperture to the anterior surface of the neck was a compromise between adequate counting statistics and minimal error due to differences in position of the thyroid. Figure 2 demonstrates the difference in count rate with changing distance from the aperture determined with the standard phantom. At the 6 cm. distance usually employed for thyroid imaging an error of cm. in placement can result in approimately 25 pen cent error in count rate. Another advantage of the longer imaging distance is that an over-all view of the neck and upper mediastinum is afforded. This enables one to see unsuspected substernal or sublingual thyroid etension. The shape of the uptake curve over the thyroid is somewhat variable. Most patients attain the maimum concentration in the thyroid by about 15 minutes, after which the count rate is fairly constant throughout the remainder of the 3 minute counting period. t is apparent in a few d - D z d Q. Cl) z U 4 X 1O3 3 2 A, - o o J.T. T.R. patients that there is continued accumulation beyond this period but, from the shape of the curve, this can only be a minimal amount. Rarely an early peak is reached after which there is a decline in count rate. The advantage of continuous recording is to be able, after the study is complete, to select the frames which contain the peak counts. Variations in 4 selected uptake curves can be seen in Figure 3, z and B. Analysis of the curves in terms of rates of uptake, correlated with clinical status, will be the subject of a later report. Field uniformity correction is important if the thyroid is some distance from the center of the image. Points in the image plane, but at the periphery of the field, will be detected with a 25 per cent lower count than points of equal activity at the center. This is due to the inverse square law. ince the angle of view of the pin_hole collimator is 33.7#{176},the distance from the aperture to the periphery is 2 per cent greaten than to _B, #{149} - #{149} #{149}. X5. XXXRZ. #{149}1 #{149}A.R. 55,#{149}#{149} f E.A. i 2 3-1 2 3 TME N MNUTE TME N MNUTE FG. 3. (A) Curves of thyroidal uptake of technetium 99 in a patient with Graves disease (T.R., uptake = 8.6 per cent), euthyroid patient (J.T., uptake= 2.12 per cent) and a patient with myedema (E.A., uptake= o.o per cent). (B) Uptake curves in a hyperthyroid patient on methimazole (A.R., uptake= 6.i6 per cent) and in a patient with non-toic nodular goiter secondary to Hashimoto s thyroiditis (R.Z., uptake=3.o2 per cent).
834 Harold L. Atkins and Johannes F. Klopper AUGUT, 1973 Downloaded from www.ajronline.org by 46.3.26.89 on 3/8/18 from P address 46.3.26.89. Copyright ARR. For personal use only; all rights reserved JG. 4. sometric display of flood field from the gamma cainera as seen on the computer display () before and (B) after field correction. the center of tile field (Fig., 1 and B). center of tile image. he usual accumula- ll practice very little difference, less tilan tion of counts over the standard is i 2- Per cent, has been observed between up- 5, counts in 3 minutes which gives very take determinations on field corrected and adequate counting statistics. A comparison uncorrected images. This is due to tile fact with our rectilinear scan uptake determithat the thyroid is usually at, or close to tile nations is seen in Table. 1AB.E COMPARON OF CAMERA AN) CANNER U AKE Uptake by Uptake b\. -... *_ - 1)ifterence Pa tlen t ) agnoss camera scanner camera-sca (per cent) (per cent) AC. NTNGf 1.9 1.7 +.2 v.\\,. NTNG.7.97 -.24 J.P. Euthvroid i.69.#{244}2 +.7 (;.W. Euthyroid.69.71 -.2 l).k. lunctioning nodule.47. 21 +.26 JO. Euthyroid i. c.77 +.76 P.R. Euthvroid i., i. i -.7 (;.K. N1N(; 2H2 J#{176} +.52 ).P. NTN(; 1.61 1.3 +.58 F;UthVroid.75.2 +.55 G.R. Futhvroid 2. 26 i. so +o. 76 T.C. NTNG.54 l..h +.21 n. Euthvroid 1.15 1.27 -.12 El. l-lvperthroid 6.46 #{231}.$#{231} \.C. Euthvrid. 1. 86 +.24 MU. Euthvroid. 12 1 o +.4 E.T. Euthvroid. 54.4 +.14 l).c. Euthyroid o.8#{231}.76 +.9 RB. Euthvroid 2.1 1.79 +.22 E.A. Euthyroid.94.67 +.18.K. Euthvroid.96 i.o -.7 Mean +.23.D. ±.24 riner * tptake b c,ner.t pcrf(rmet at apprui mate1 c mnutes after scanner uptake and appr)lnlatelv - #{231} minutes f Ni N;= non-toxc nodular goiter. after injection.
VOL. 1i8, No. 4 Thyroidal Technetium Uptake 835 Downloaded from www.ajronline.org by 46.3.26.89 on 3/8/18 from P address 46.3.26.89. Copyright ARR. For personal use only; all rights reserved Field uniformity corrections for the short distance thyroid images have not resulted in changes in interpretation despite the fact that the images fill nearly the entire field. This is probably because the gradual change in sensitivity from the center to the periphery of the field is not large enough to affect the perception of the image. The method described differs from that of Hunley et al. in that the time for determination of uptake is individually determined from the uptake curve. n addition, the determination is performed at a greaten pin-hole to neck distance and field response correction is used. CONCLUON The determination of technetium 99 uptake in the thyroid can be a useful clinical method. The variation in time of peak accumulation in the thyroid is moderate. Continuous recording over the thyroid using a gamma camera and a data processing system, while time consuming, can improve the accuracy of these determinations compared to those performed with the rectilinear scanner. Harold L. Atkins Medical Department Brookhaven National Laboratory Upton, Long sland, New York 973 This study was performed tinder the auspices of tile United tates Atomic Energy Commission. REFERENCE. ATKNs, H. L. Technetium-99m pertechnetate uptake and scanning in evaluation of thyroid function. eminars Nuclear Med., 1971, 1, 345-355. 2. ATKN, H. L., and RCHARD, P. Assessment of thyroid function and anatomy with technetium-99m as pertechnetate. 7. Nuclear Med., 1968, 9, 7-15. 3. HECK, L. L., and Go1-T5CHALK, A. Rapid and reproducible method for 99mTc thyroid uptakes. 7. Nuclear Med., 197,, 325 (Abstr.). 4. HOLME, R. A., NORTH, W. A., and KARMEN, A. Trapping of pertechnetate by thyroid. 7. Nuclear Med., 967, 8, 336-337 (Abstr.). 5. HURLEY, P. J., MAEY, M. N., NATARAJAN, F. K., and WAGNER, H. N., JR. Computerized system for rapid evaluation of thyroid function. 7. C/in. Endocrinol., 1972,34, 354-36. 6. HURLEY, P. J., TRAU, H. W., PAVON, P., LANGAN, J. K., and WAGNER, H. N. cintillation camera with pinhole collimator in thyroid imaging. Radiology, i971, 11, 133-138. 7. PALOYAN, D., HENDRCK, K. D., GOTTCHALK, A., and HARPER, P. V. Early thyroid uptake measurements using gamma scintillation camera-6 channel analyzer. 7. Nuclear Med., 1967, 8, 336 (Abstr.). 8. ROBNON, T., COLLCA, C. J., and CHANG,. Clinical comparison of scans and scintiphotos of thyroid gland. AM. J. ROENTGENOL., RAD. THERAPY & NUCLEAR MED., 1968, 13, 738-745. 9. WLLAM, E. D., GLA, H.., GOOLDEN, A. W. G., and ATYAVANCH,. Comparison of two methods of measuring thyroidal uptake of 99mTc. 7. Nuclear Med., 1972, /3, 59-162.