Медицина/16. Лучевая диагностика

Smirnov I. E., Gerasimova N. P., Komarova N. L., Kogtev L.S.

Scientific Centre of Children’s Health of the Russian Academy of Medical Sciences

A NEW METHOD FOR ESTIMATION OF THE VOLUME OF FUNCTIONALLY ACTIVE RENAL TISSUE IN CHILDREN

The proposed method for the determination of functionally active renal tissue is based on the utilization of short-living radionuclide — technetium (^99mТс) with the half-life of 6 hours and soft γ-radiation with the energy of 140 keV, that makes the diagnostic procedure safe, enabling to reduce the radiation exposure for patients in several tens times[1].

The authors have proposed the new method for the determination of the volume of the functionally active renal parenchyma and estimation of renal function disorders by administering of radiolabeled compounds into the patient’s body. In the ideal situation, radiologist should have the acceptable examination strategy, providing the reliable and necessary information, in order to use it as the guideline for the making of the diagnostic decisions. The above information should be considered objectively during the analysis of examination data and based upon the most advanced technologies providing the high level for performance of diagnostic procedures [2].

The method for diagnostics of viability of renal parenchyma is known, when the patient is intravenously administered with the RP (tracer), comprising of diethylene triamino pentaacetate (DTPA), labeled with short-living radionuclide ^99mТс with the activity of 60-600 megabecquerelles (MBq), determined using the dose calibrator. The abovementioned RP is selectively filtered by the glomerulous renal apparatus. The time of maximal accumulation and clearance of the half-quantity of RP from the kidney is used for the conclusion of renal parenchyma viability [3].

Also the method for diagnostics of renal parenchyma viability is known, wherein the patient is administered intravenously with the RP, which is the dimer of captosuccinic acid (DMSA), labeled with short-living radionuclide ^99mТс with the activity of 80-600 MBq, determined using the dose calibrator [4]. The above complex (DMSA—^99mТс) is selectively captured by the renal tubules and retained therein for 4-6 h. After 2-4 h post-injection of RP, acquisition of scintigrams for two (anterior and posterior) or several projections is performed using gamma camera with the interruption of recording when 200000-1000000 counts for one projection is achieved.

Using scintigram, the uptake of RP with the each kidney is estimated by the calculation of the total amount of counts from the kidney (in kilocounts) for anterior and posterior images, and subtraction of counts, coming from the surrounding tissues. Renal parenchyma viability is assessed based on the distribution of RP, which is calculated by comparing uptake of RP by one kidney relatively of the both kidneys, taking the uptake of RP for the both kidneys as 100%. Normally, this value is of 45-55%. When the viability of parenchyma of one kidney is disordered the distribution of tracer is reduced. This method suffers from low information content in the cases with the symmetric lesion of the both kidneys and in patients with the single kidney [5]. Along with the above techniques the method for evaluation of viability of renal parenchyma was proposed. This method comprises intravenous administration of RP, activity of which is previously measured with the dose calibrator. After 2 h post-injection of RP, static scintigrams are recorded, and calculation of uptake of the RP and its distribution with the consequent calculation of integral uptake indice for each kidney are performed. Values of the latter within the range from 45 to 70 demonstrate the normal viability of renal parenchyma, and for values less than 45 disorders of renal parenchyma viability is diagnosed.

However, the significant disadvantage of said method is impossibility for the total estimation of renal functional condition and their separate segments, since the acquisition in the static mode is long-lasting, and the long continuous presence of the patient within the diagnostic department is required for this purpose (more than 2 h after intravenous administration of RP), that is especially difficult for the infants and children before 7 years; the interruption of acquisition and correction for radioactive decay of RP are also necessary.

In connection with the above the authors have developed the novel method for evaluation of the volume of the functionally active renal parenchyma by the performance of dynamic scintigraphy.

This object is achieved by the following manner: the patient is intravenously administered with 37-185 MBq of RP "Тechnemag^99mТс", which activity is measured in the syringe before and after injection, and then over 20 min, the dynamic scintigraphy of kidneys is performed, that is consequent series of scintillation images at different moments of time. The acquisition program includes the continuous recording of frames over 20 min with the exposition time for each frame of 20 sec. Within the period of maximal accumulation of RP in kidneys (120 sec) uptake activity of RP is estimated by the calculation of number of counts in the regions of interests (ROI) on the scintigram, corresponding to the left (Ns) and right (Nd) kidneys, and in the regions of soft tissues positioned below the images of the corresponding kidneys (ns and nd, respectively).

The volume of the functionally active renal parenchyma (VFP) is calculated for each kidney by the formula:

wherein VFP(s) and VFP(d) — volumes of the functionally active renal parenchyma for the left and right kidneys, respectively; Q_x — activity in the full syringe before administration of RP; Q₂ — activity of RP in the syringe after injection; Q₃ — activity at the site of administration of RP.

Total volume of the functionally active renal parenchyma is determined by the summation of VFP(s) and VFP(d).

Examinations conducted by the authors showed that calculated values of VFP(s) and VFP(d) for each non-damaged kidney vary from 6,4 to 8,1 units, that demonstrates normal volume of the functionally active renal parenchyma in children. Total (overall) volume of the functionally active renal parenchyma equal to VFP(s) + VFP(d) for arbitrary healthy children is in the range from 12,8 to 16,2 units.

For the estimation of diagnostic significance and sensitivity of the proposed method for the evaluation of the volume of the functionally active renal parenchyma in children, the authors has conducted its comparative analysis with the prototype. Using the above described procedure we have performed examinations for 63 infant patients of the age from 1 year to 15 years with the different forms of renal and urinary tract pathology, including 26 patients with hydronephrosis, 15 infants with megaurether, 14 — with vesicoureteral reflux and 8 patients with renal hypoplasia.

The conducted studies demonstrated high diagnostic value and sensitivity of the proposed method for estimation of functional renal condition using RP "Тechnemag⁹⁹Тс" (specificity and reproducibility of the method was of 59%). The deviations of RP uptake have been shown for 26 children.

The proposed method for the determination of the RP uptake by each kidney and total uptake by the both kidneys has high diagnostic significance, enables faster and more effective detection of disorders associated with the volume of the functioning renal tissue for the large number of patients with various forms of renal pathology, since it saves time required for acquisition and is characterized by the higher information value for the reason that determination of functioning renal parenchymal volume based on uptake activity of RP is performed using dynamic scintigraphy, with the lower radiation exposure for the patient (by 2,1-3,2 times), and during the examination the interruption of acquisition and correction for radioactive decay are not required.

Thus, the utilization of said method, described above, enables to accelerate significantly the examination of the infant patient, to determine precisely volumes of the functionally active renal parenchyma for the different forms of pathology thereof in children irrespectively of age, to optimize substantially the prognosis of outcomes and reduce the risk of chronic renal insufficiency.

Литература:

1. Itoh K. 99mTc-MAG3: review of pharmacokinetics, clinical application to renal diseases and quantification of renal function. Ann. Nucl. Med., 2001;15(3):179-190.

2. Szabo Z, Alachkar N, Xia J, Mathews WB, Rabb H. Molecular imaging of the kidneys. Semin Nucl Med. 2011; 41(1):20-28.

3. Durand E, Chaumet-Riffaud P, Grenier N. Functional renal imaging: new trends in radiology and nuclear medicine. Semin Nucl Med., 2011; 41(1):61-72.

4. Bhatt M.K., Bartlett M.L., Mallitt K.A., et al. Correlation of various published radionuclide glomerular filtration rate estimation techniques and proposed paediatric normative data. Nucl Med Commun., 2011; 32(11):1088-1094.

5. Ansari-Gilani K, Gholamrezanezhad A, Beiki D, Mirpour S, Modaresi Esfeh J. Renal axis deviation in urinary tract abnormalities of children: the role of renal scintigraphy. Clin Nucl Med., 2011; 36(12):1086-1091.