Richard Bauer

In vivo/in vitro labeling of red blood cells with 99mTc

Red blood cells (RBC) were labeled with 99mTc in vitro after in vivo pretreatment with a stannous solution. The whole in vivo/in vitro procedure took 30–40 min. Pretinning was carried out by injection of either 6 mg DTPA and 0.6 mg Sn++ (Sn-DTPA) or 5 mg pyrophosphate and 0.7 mg Sn++ (Sn-PYP). The results of 1,356 patients were evaluated. The labeling yield was 89.7% (mean) after pretinning with Sn-DTPA and 88.2% following Sn-PYP pretreatment, the median values being 94% and 92%, respectively. The new method was successfully used in over 2,000 patients who had a radionuclide-ventriculography and in 38 patients studied for localization of occult gastrointestinal bleeding. Adverse side effects have never been observed.

Tc-generators — Yield of 99mTc and ratio to ‘inactive’ 99Tc

A large amount of inactive 99Tc in some delicate labeling techniques may adversely affect the results obtained. Therefore, it is important to know the ratio (Q(t) of inactive 99Tc to active 99mTc, which is dependent on the time (t) elapsed since the last elution. On the other hand, in optimizing the use of Tc-generators it is desirable to know the actual yield Y(t) at any time (t) after a preceding elution. In this paper, formulas both for Q(t) and for Y(t) are derived and numerical values are tabulated. In combination with a table of the amount of 99Mo left, M(t), all the properties of a Tc-generator and of its eluates may be derived and theoretical and practical results compared. This information will help in both optimizing the use of Tc-generators and improving quality control in radiopharmaceutical laboratories.

Comparison of magnetic resonance imaging with cross-sectional echocardiography in the assessment of left ventricular mass in children without heart disease and in aortic isthmic coarctation☆

Although left ventricular (LV) mass may be important to judge effects of left-sided cardiac obstruction or hypertension, reproducible noninvasively determined normal data in the pediatric age group are scarce. To validate cross-sectional echocardiographic LV mass determination, our data were compared with LV mass assessed by magnetic resonance imaging (MRI). MRI was considered to be a good reference method because there is usually no problem in defining endo- and epicardial borders with MRI. LV mass was assessed in 14 children aged 5.3 years (10 days to 14.7 years) with a mean body surface area of 0.78 m2 (range 0.25 to 1.61). With cross-sectional echocardiography the epicardial and endocardial volumes were calculated using a Simpsons rule algorithm in the apical 2- and 4-chamber view. The difference between epi- and endocardial volumes was multiplied by 1.05 to yield the mass. Mass was assessed with MRI using a multislice technique; the area of each myocardial slice was calculated and multiplied with the slice thickness, and the resultant slice volumes were added to obtain the myocardial volume. On cross-sectional echocardiography, the mass was 55 g (range 12 to 126) or 64 g/m2 (range 46 to 79); on MRI it was 60 g (range 33 to 87) or 69 g/m2 (range 46 to 89). Regression analysis yielded an r value of 0.98 with a standard error of the estimate of 5.7 g or a 10% difference. In older children, LV mass determined by MRI was bigger than the one derived by echocardiography. It is concluded that cross-sectional echocardiography can reliably assess LV myocardial mass in pediatric patients.

Diagnosis of focal nodular hyperplasia with hepatobiliary scintigraphy using a modified SPECT technique.

A 29-year-old woman was examined because of malnutrition and recurrent diarrhea. Her serum glutamate oxaloacetate transaminase and serum gamma glutanyl transferase (SGGT) levels were found to be elevated. The patient denied alcohol abuse, blood transfusion, and foreign travel, and she had never used oral contraceptives. Findings of ultrasonography of the liver were normal. A computed tomographic examination suggested focal nodular hyperplasia (FNH), although adenoma could not be excluded. Hepatobiliary imaging was normal and did not manifest the three typical signs of FNH: hypervascularization, increased tumor uptake, and trapping in later images. Repeated scintigraphy using a modified SPECT technique clearly showed FNH.

Inquiry to standardize nuclear-medical functional investigations

The Society of Nuclear Medicine of Europe (SNME) and the European Society of Nuclear Medicine (ESNM) have established a joint task group in order to standardize functional studies in nuclear medicine. In recent years, similar task groups have been set up for the same purpose, and many workshops have been held, in which suitable standards in functional nuclear-medical investigations have been discussed. As a result of these efforts, minimum requirements with regard to hardand software have been established. However, the ultimate aim of establishing standards and procedures that are accepted worldwide has not yet been realized. In particular, quantitative functional parameters, as assessed by different institutions and investigators, are not comparable. We want to attempt another approach to the standardization of functional parameters and investigational protocols, starting from the physiological definition of appropriate functional parameters. Many parameters such as the ejection fraction and the clearance of the kidneys have a clear physiological definition. In nuclear-medical investigations, these parameters cannot be directly determined according to the original physiological definition, but certain restrictions have to be made, because nuclear medicine, owing to its non-invasive approach, gives indirect results. When comparing functional parameters obtained by different investigators, the hardware configuration of the computer and gamma camera as well as the speed and effectiveness of the software used are of minor importance, whereas the mathematical implications as well as the simplifications and assumptions made are crucial to the quantitative value of the result obtained. Although nuclear-medical investigations often provide other functional data of clinical relevance, these data lack directly comparable and corresponding physiological equivalents. An example of such a parameter is the maximal rate of volume change during diastole (VD), which correlates with the shortening of the heart-muscle fibers without having a one-to-one correspondence to it. It is particularly important that these parameters and the procedure to assess them are standardized, because there is no physiological equivalent which could serve as a standard. Recently, parametric images have acquired increasing interest and importance. Parametric images of the ampli-

Radiation synovectomy of the knee joint : Evaluation of bremsstrahlung-detection by using a corpse phantom

AIM Multiple procedures for the quantification of activity leakage in radiation synovectomy of the knee joint have been described in the literature. We compared these procedures considering the real conditions of dispersion and absorption using a corpse phantom. METHODS We simulated different distributions of the activity in the knee joint and a different extra-articular spread into the inguinal lymph nodes. The activity was measured with a gamma-camera. Activity leakage was calculated by measuring the retention in the knee joint only using an anterior view, using the geometric mean of anterior and posterior views, or using the sum of anterior and posterior views. The same procedures were used to quantify the activity leakage by measuring the activity spread into the inguinal lymph nodes. In addition, the influence of scattered rays was evaluated. RESULTS For several procedures we found an excellent association with the real activity leakage, shown by an r(2) between 0.97 and 0.98. When the real value of the leakage is needed, e. g. in dosimetric studies, simultaneously measuring of knee activity and activity in the inguinal lymph nodes in anterior and posterior views and calculation of the geometric mean with exclusion of the scatter rays was found to be the procedure of choice. CONCLUSION When measuring of activity leakage is used for dosimetric calculations, the above-described procedure should be used. When the real value of the leakage is not necessary, e. g. for comparing different therapeutic modalities, several of the procedures can be considered as being equivalent.