DIAGNOSTIC TECHNIQUE FOR SURGICAL THYROID DISEASES USING DYNAMIC DOUBLE-INDICATOR SCINTIGRAPHY

摘要

FIELD: medicine.;SUBSTANCE: invention refers to medicine, namely to radionuclide diagnostics, and can be used for diagnostics of thyroid gland surgical diseases with application of dynamic double-indicator scintigraphy of thyroid gland. Research is carried out using a multi-detector gamma camera equipped with low-energy high-resolution collimators. Scintigraphy is performed in the patient's position lying on his/her back with his head thrown back. Detector is placed at a minimum distance from the front surface of the neck. Anatomical landmarks are selected from a cyst-shaped cartilage from above and a jugular tenderloin from below. It is considered important to maintain stable position of patient during examination in order to avoid false-positive and false-negative results. There are two stages of the study: the first stage involves the intravenous introduction of ^99mTc-pertechnetate. Depending on the age and body weight, a radiopharmaceutical with specific activity of 50–100 MBq is administered to the patient, 20 minutes after the injection of which, plane images of the anterior neck are obtained with the following examination parameters: digital zoom: 3.2; matrix: 256 × 256; set of pulses per each frame: 500 Kcounts. Testing time: 300 s; gamma-ray energy: 140 ± 20 keV. Second stage is started after intravenous introduction of 400–700 MBq ^99mTc-technetryl introduced 5 minutes after the end of scanning with ^99mTc-pertechnetate. In the same patient's position, the patient is subjected to dynamic scanning for 35 minutes and additionally static scan is performed in 60 minutes, followed by 10 scintigram results in the early scanning phase and 60 minutes with a later phase of scanning after injection of tumour-tropic radiopharmaceutical with the following study parameters: digital zoom: 3.2; matrix: 128 × 128; set of pulses per each frame: 50 Kcounts; gamma-ray energy: 140 ± 20 keV. To improve the quality of images, standard smoothing of the native image and subtraction of the fabric background are carried out. Primary evaluation of the scintigrams obtained by scanning with ^99mTc-pertechnetate is based on their qualitative or visual analysis: thyroid location, size, contours, presence of aberrant tissue, uniform distribution of radiopharmaceutical, presence and localization of pathological centre, its value, contour, shape are determined. Nodular formations are generally considered to be hyperfunctioning or "hot" when absorbing radiopharmaceutical in them higher than in normal thyroid tissue, functioning or "warm" and non-functioning or "cold" with no absorption of radiopharmaceutical in them. After subtraction of images in a projection of nodules found at the first stage of the study, the nature of the accumulation of a tumour-tropic radiopharmaceutical is evaluated. That is followed by using a modified high-quality visual technique for estimating scintigrams, using a system based on isolation of 3 models of nodules depending on absorption of ^99mTc-pertechnetate and ^99mTc-technetryl: Model 1 - absorption of ^99mTc-technetryl below absorption of ^99mTc-pertechnetate; Model 2 - absorption of ^99mTc-technetryl above absorption of ^99mTc-pertechnetate in early scanning phase; absorption of ^99mTc-technetryl in early scanning phase is higher than absorption of ^99mTc-technetryl in late phase; Model 3 - absorption of ^99mTc-technetryl above absorption of ^99mTc-pertechnetate in early scanning phase; absorption of ^99mTc-technetryl in early scanning phase is lower or equal to absorption of ^99mTc-technetryl in late phase. Nodal structures regarded primarily as "hot", as well as corresponding 1^st and 2^nd models, are considered to be benign. Model 3 is characterized by presence of signs of malignant growth. Further, in order to increase the informative value of the dynamic double-indicator scintigraphy of the thyroid, an original semi-quantitative analysis technique is used, based on an evaluation of the leaching index or LI of ^99mTc-technetryl in the early and late scanning phases, for this purpose, early scintigrams are used to construct an area of interest or AI around nodules and its projection outside the thyroid in the supraclavicular region in order to subtract the background absorption region or BAR of the radiopharmaceutical. Said AI and BAR are copied to delayed scintigrams. To calculate the LI, average capture parameters of ^99mTc-technetryl in AI and in BAR are given in numerical equivalent. Thus, LI is calculated as ratio of average RPP capture taking into account subtraction of its background absorption in nodules in late and early scanning phases, expressed in percentage. Formula for calculating LI is presented as follows: medium absorption of ^99mTc-technetryl in AI in early scanning phase - average absorption of ^99mTc-technetryl in BAR in early scanning phase = early result or ER; medium absorption of ^99mTc-technetryl in AI in late scanning phase - average absorption of ^99mTc-technetryl in BAR in late scanning phase = late result or LR. LI = 100−LR/ER × 100. Using the given technique, it is suggested that the nodular formations with the LI of radiopharmaceutical agent more than 20 % correspond to the benign tumour, and less than 20 % - malignant. In the first case, the patient is justified to remove a portion of the thyroid gland, in the second - to perform hemithyroidectomy or thyroidectomy.;EFFECT: method provides differential diagnostics of malignant thyroid formations by determining ^99mTc-technetryl leaching index and nodule patterns depending on their ^99mTc-pertechnetate and ^99mTc-technetryl absorption values.;1 cl, 2 ex, 9 dwg