Evaluation of exercise-induced stunning using myocardial perfusion imaging.

A late reduction (i.e. 1 hour post exercise) in left ventricular ejection fraction (LVEF) in patients with ischaemic heart disease was recently reported with radionuclide myocardial perfusion imaging (MPI). This was ascribed to possible stunning provoked by exercise-induced ischaemia. The purpose of this retrospective study was to evaluate the possible relationship between exercise-induced ischaemia and late (1 hour) post-exercise myocardial stunning. Forty-eight patients who underwent standard treadmill exercise with 99m Tc-MIBI MPI were analysed according to their rest and stress perfusion images. A normal group of 15 subjects, 23 patients with previous infarction and 10 with objective evidence of ischaemia were identified. Absolute change, i.e. exercise LVEF minus rest LVEF, and relative change, i.e. absolute change divided by resting LVEF (expressed as a percentage) were determined. The mean absolute change in LVEF was not significant within the normal and infarction groups but was statistically significant within the ischaemic group. The mean relative ( %) change within the normal and infarction groups was not significant, but was significant within the ischaemic group. The difference in mean absolute changes between the normal and infarction group was not significant but both these groups were statistically different when compared with the ischaemic group. No statistically significant difference in mean relative changes was found between the normal and infarction groups. The mean relative change in the ischaemic group tended to be larger than in the infarction group. The presence of a late regional wall motion abnormality or decreased LVEF after exercise (i.e. stunning) may be an important additional indicator of underlying myocardial ischaemia.

Left ventricular ejection fraction calculated from gated technetium-99-sestamibi SPECT.

BACKGROUND: The accuracy of the left ventricular ejection fraction (LVEF) calculated from gated single photon emission computed tomography (GSPECT) studies is dependent on the accuracy of the determination of the end-diastolic volume (EDV) and end-systolic volume (ESV) of the left ventricle (LV). In this study we evaluated the feasibility of calculating the EDV, ESV and LVEF from the area under the polar graph (APC) of the edges of the LV image determined by a first derivative edge-detection method. METHODS AND RESULTS: Technetium-99m ((99m)Tc) sestamibi GSPECT studies and planar equilibrium radionuclide ventriculography (ERNV) were performed on 15 male subjects in whom the LVEF ranged from 19% to 75%. Images were reconstructed to obtain short axis slices of the LV spanning the cardiac cycle. On each slice the LV edge points were determined at 10 degrees intervals using the APC method. The area of each short axis slice was determined by conversion to polar co-ordinates, interpolation and numerical integration of the graphs and multiplication by a pre-determined conversion factor. RESULTS: Edges were successfully determined in all 15 patients using the APC method. The LVEF results correlate well with conventional planar ERNV studies (r = 0.96, LVEF(GSPECT) = 8.80 + 0.66 LVEF( ERNV)). The absolute difference between the LVEF for ERNV and for the APC method was 6.1% with a standard deviation of 7.6%. The reproducibility of SPECT LVEF using the APC method was good (intra-observer r = 0.99, inter-observer r = 0.99). CONCLUSIONS: The APC method provides for easy and accurate ejection fraction determination with limited underlying mathematical assumptions. The ability to interpolate the edge points provides for stable edge detection even in hypoperfused myocardium.

Implementation of a Tc-99m and Ce-139 scanning line source for attenuation correction in SPECT using a dual opposing detector scintillation camera.

Image degradation during single photon emission computed tomography (SPECT) due to attenuation and Compton scatter of photons can cause clinical image artifacts and will also result in inaccurate quantitative data. Therefore attenuation correction methods recently received wide interest. Transmission imaging can be performed to obtain the attenuation coefficients of a nonhomogeneous attenuating medium accurately. The aim of this study was firstly to evaluate the imaging characteristics of the scanning line source assembly. The results obtained with Tc-99m and Ce-139 were compared. Secondly the calculated attenuation coefficients were compared with known values from literature, using Tc-99m and Ce-139 as transmission sources. Lastly the method of acquiring simultaneous transmission and emission data was investigated. This study shows that an attenuation coefficient map can be obtained using a scanning line source for transmission imaging with a dual opposing detector camera. The imaging characteristics of Tc-99m and Ce-139 as transmission sources are similar. The resolution obtained with the Ce-139 line source was poorer than that obtained with the Tc-99m line source. A linear relationship was found between CT numbers and attenuation coefficients for transmission images using both Tc-99m and Ce-139 line sources. The attenuation coefficient value for water was underestimated by 1% using the Tc-99m transmission source and underestimated by 10% using Ce-139 as transmission source. This underestimation of attenuation coefficient values was also obtained in the human study. A myocardial perfusion study processed without and with attenuation correction clearly demonstrated the effect of the attenuation correction in the inferior myocardial region. The potential of using a scanning line source as transmission source with a dual opposing detector camera has been demonstrated in this study. The transmission source, Ce-139 was successfully introduced in this investigation for simultaneous acquisition of transmission and emission data.

Measurement of plasma volume using 99Tc(m)-labelled DMP-HSA.

Red cell volume (RCV) and plasma volume (PV) measurements are performed routinely in nuclear medicine departments to diagnose a number of haematological disorders. Currently, 125I-HSA is used as a plasma tracer and 99Tcm-labelled red cells to determine red cell volume. 125I-HSA is not always readily available, leading to inconvenience for patients and medical practitioners. Due to the availability of 99Tcm in nuclear medicine departments, the use of albumin labelled with 99Tcm was investigated. A new 99Tcm-human serum albumin labelling kit (99Tcm-DMP-HSA) was developed by Verbeke and supplied for use in this study. The main aim of the study was to investigate the use of 99Tcm-DMP-HSA for PV determination. Secondly, the feasibility to determine red cell and plasma volume simultaneously using 99Tcm as radionuclide in both instances was investigated. Fourteen healthy volunteers were enrolled in the dual-phase study. During the first study, 99Tcm-DMP-HSA was used as tracer to calculate PV (PV1a) after intravenous administration. Subsequently, 99Tcm-labelled red cells were administered and the PV (PV1b) and RCV (RCV1) were calculated. The second study was repeated within 2 weeks using the conventional method. 125I-HSA and 99Tcm-labelled red cells were administered simultaneously. The PV (PV2) and RCV (RCV2) were calculated. We found that the redistribution of 99Tcm-DMP-HSA is faster than that of 125I-HSA; therefore, the plasma counts obtained at different times were back-extrapolated to time zero for plasma volume calculations. The mean values for the different calculated PVs were 2964+/-470 ml for PV1a, 3006+/-623 ml for PV1b and 3001+/-530 ml for PV2, the reference PV. The confidence intervals indicate no significant differences between plasma volumes PV1a and PV2 and plasma volumes PV1a and PV1b. The mean calculated RCV1 was 2130+/-322 ml; that of RCV2 was 2128+/-353 ml. The difference between RCV1 and RCV2 was not significant. Our results indicate that 99Tcm-DMP-HSA could be used for plasma volume calculation. Red cell and plasma volumes can be calculated simultaneously using 99Tcm as radionuclide in both cases.

Biodistribution and absorbed radiation dose estimates of 99mTc-labeled dimercaptopropionyl human serum albumin.

UNLABELLED: The use of 99mTc-labeled red blood cells (RBC) for the evaluation of left ventricular function using equilibrium-gated blood-pool imaging suffers from several problems and potential risks. In this study, we estimated the absorbed radiation dose of 99mTc-labeled dimercaptopropionyl human serum albumin (DMP-HSA) as a potential alternative to 99mTc-RBC. METHODS: After the administration of 99mTc-DMP-HSA, whole-body imaging was performed up to 48 h after injection in five volunteers. The heart contents, liver and remainder of the body were used as source organs. Multicompartment modeling of the biodistribution was performed and absorbed radiation dose estimates for 99mTc-DMP-HSA were obtained using the Medical Internal Radiation Dose (MIRD) calculation. RESULTS: Residence times of 0.62 and 0.43 h were obtained for the heart contents and liver, respectively. Radiation dose estimates yielded an effective dose of 0.0055 mSv/MBq. CONCLUSION: 99MTC-DMP-HSA yielded absorbed radiation doses comparable with those of 99mTc-RBC. Therefore, the radiation properties of 99mTc-DMP-HSA are such that it can be used for clinical diagnostic studies.

Radiation dose estimates of 186Re-hydroxyethylidene diphosphonate for palliation of metastatic osseous lesions: an animal model study.

A common complication in patients with breast or prostate cancer is bone metastases causing pain. New radionuclide therapy methods have recently been proposed for palliation, including 186Re-hydroxyethylidene diphosphonate (186Re-HEDP). This paper reports on the local development of 186Re-HEDP and the biodistribution studied in animals for eventual use in patients. Adult dose was computed assuming a 70 kg standard man. The 186Re was labelled to HEDP using standard techniques. The biodistribution in five Chacma baboons (Papio ursinus) was studied. Doses ranging from 39.4 to 44.9 MBq kg(-1) (mean 43.6 +/- 2.8 MBq kg[-1]) were administered, corresponding to an adult human dose of 2960 MBq (80 mCi). Whole-body images of the animals were obtained with a dual-headed scintillation camera on an hourly basis for 6 h post-injection and then daily for 3 days. The bone, soft tissue, kidneys and urinary bladder were considered source organs and data from these organs were used in a compartmental model to obtain the mean residence times of the radionuclide in the different source organs. Radiation dose estimates for 186Re-HEDP were subsequently obtained with the MIRDOSE 3 program. The estimated absorbed radiation doses to some of the organs (expressed in mGy MBq[-l]) were as follows: bone surface 1.69; kidneys 0.09; liver 0.04; ovaries 0.04; red marrow 0.75; total body 0.12; urinary bladder wall 0.43. 186Re-HEDP yielded an effective dose of 0.17 mSv MBq(-1). The radiation dose delivered to the bone marrow in this study did not cause any detrimental effect to the baboons, indicating that locally produced 186Re-HEDP is suitable for clinical use.

Evaluation of reflux oesophagitis with technetium-99m-labelled sucralfate.

UNLABELLED: Sucralfate binds with denuded protein to form a stable complex to protect the damaged mucosa. By utilising this property, technetium-99m-labelled sucralfate can be used to demonstrate ulceration in the upper gastro-intestinal tract. AIM: The aim of this study was to evaluate 99mTc-labelled sucralfate in the diagnosis of grade II-III reflux oesophagitis. METHODS: Ten patients with endoscopic proof of grade II-III reflux oesophagitis and 10 patients with normal findings on oesophagoscopy were evaluated after they had swallowed 5 ml 99mTc sucralfate. Radionuclide imaging was done until activity in the oesophagus had ceased. RESULTS: Retention of activity from 10 minutes up to 1 1/2 hours could be demonstrated in 9 patients with endoscopically proven oesophagitis. In the control group complete clearance of activity was seen in 7 patients. Gastro-oesophageal reflux could be demonstrated in 4 patients. CONCLUSION: In conclusion we found 99mTc sucralfate to be a sensitive and specific method for the non-invasive diagnosis of grade II or grade III oesophagitis when compared with endoscopy [corrected].

The effect of exercise on normal splenic volume measured with SPECT.

In a study group of 20 healthy young men, splenic volume was determined with SPECT before and after exercise. A randomly chosen control group of 10 comparable men was studied similarly, but without exercise intervention. The mean splenic volume did not change significantly in the control group (i.e., from 292.9 ml to 282.1 ml [P = 0.75]). The mean splenic volume decreased 60.1 ml from 279.4 to 219.3 ml (21.5%) in the study group and this was highly significant (P = 0.01). Although exercise induced splenic autotransfusion is generally considered to be unimportant in humans, significant splenic contractility was observed with this technique. In the normal individual with a large spleen or with functional splenomegaly, the contractility response may become more important and can now be measured in a quick and easy manner.

Determination of glomerular filtration rate with radionuclide renography and direct urinary activity quantitation.

OBJECTIVE: The direct urinary activity quantitation method is quick (approximately 40 minutes), requires only a single blood sample, is performed as part of standard renal scanning and shows high accuracy compared with 24-hour creatinine clearance. The purpose was to evaluate the practical application and accuracy of this technique at our clinic. DESIGN: Direct urinary activity quantitation was done in patients scheduled for routine radionuclide renography and compared to standard multiple-blood-sample techniques by means of Cr-51-EDTA and Tc-99m-DTPA. SETTING: Academic Medical Complex, Department of Nuclear Medicine, Universitas Hospital, Bloemfontein. PARTICIPANTS: Fifteen patients scheduled for routine radionuclide renography (glomerular filtration rate (GFR) determination) were voluntarily enrolled in the study. The GFRs of selected patients varied over a wide range. Possible obstructive uropathy was excluded. MAIN OUTCOME MEASURES: GFRs obtained by the direct urinary method were compared with GFRs determined by multisample Cr-51-EDTA and Tc-99m DTPA. RESULTS: GFRs from the direct urinary method compared with multisample Tc-99m-DTPA showed differences from -19.85 to 22.95 ml/min with a mean of 0.2 (+/- 12.25) ml/min (r = 0.93). When compared with multisample Cr-51 EDTA, differences ranged from -34.35 to 21.05 ml/min with a mean of -4.25 (+/- 16.08) ml/min (r = 0.90). CONCLUSION: The direct urinary activity technique is CONCLUSION: The direct urinary activity technique is easily applied and highly accurate compared with previous standardised multisample radionuclide techniques for determination of GFR.

Difference between splenic volume measured at necropsy and that measured in vivo by radionuclide tomography.

Reference values for splenic volume used in this study are based on necropsy measurements made in 1970. Because the volumes (measured by radionuclide tomography) seemed to be consistently greater than the necropsy values, the splenic volume in 35 healthy male volunteers ranging in age from 18-30 years (median age, 21 years) was studied. Their mean (SD) splenic volume was 281 (73) ml compared with 138 (34) ml in the reference group. The mean splenic volume in healthy volunteers seems to be significantly greater than in cadavers, and these results suggest that reference range for splenic volume in vivo should be revised.

Staff radiation doses during eight years in a nuclear medicine radiopharmacy.

It is important that staff radiation doses be kept 'as low as reasonably achievable' (ALARA). Staff working in the radiopharmacy and nursing staff responsible for injecting radionuclides are being monitored constantly in our department. We report here on the effective doses and doses to the hands received by staff at two hospitals during 8 years from January 1985 to December 1992. In addition to the doses determined monthly by the South African Bureau of Standards' Radiation Protection Service (SABS), radiation doses received to the hands and whole body were measured every week using lithium fluoride thermoluminescent dosimetry (TLD). The workload (number of patient studies each year) and the estimated amount of 99Tcm received per month were also established, and results have been expressed in relation to these where possible. The combined radiation doses and the absorbed dose per unit activity a single radiographer would have received, since 1988 when radiopharmacy duties were centralized, were calculated. The highest total radiation dose received in any one year by any one person at hospital A was 223.53 mSv to the hands, and 10.20 mSv and 8.37 mSv to the whole body depending on the dosimeter used. The corresponding values for hospital B were 54.05 mSv to the hands and 6.94 mSv and 4.43 mSv to the whole body. If only one radiographer should do all the work the calculated highest dose received would be 447.06 mSv to the hands and 9.68 mSv SABS effective dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Verification of a varying threshold edge detection SPECT technique for spleen volume: a comparison with computed tomography volumes.

SPECT enables quantitation of organ volume with radionuclide techniques using threshold edge detection methods. Previous phantom studies showed that a negative correlation exists between volume and threshold value. In those studies, the use of calibration curves were believed to correct for volume dependence on threshold values. The aim of this study was to evaluate the accuracy of spleen volume determination in 20 patients with SPECT by employing a varying threshold edge detection technique with volumes derived from CT. All patients had both radionuclide and CT examinations that were reconstructed with a filtered backprojection algorithm. During SPECT reconstruction, transverse slices were obtained with attenuation correction (Method A) and without attenuation correction (Method B). CT volumes were calculated from manually drawn regions of interest, whereas SPECT volumes were calculated with an automated algorithm using previously determined calibration curves. A confidence interval for calculated SPECT volumes also was calculated because of possible errors in the threshold value. The spleen volumes studied ranged from 91.2 ml to 1660.1 ml. Regression analysis yielded equations of CT = 0.97 SPECT + 7.07 (r = 0.996) and CT = 1.05 SPECT - 19.25 (r = 0.990) between CT and SPECT spleen volumes with a standard error of the y estimates of 31.10 ml and 54.47 ml, respectively. A mean percentage difference of 10.5% +/- 7.6% and 11.4% +/- 6.6% in spleen volume was obtained for Methods A and B in comparison with CT spleen volumes. The threshold value varied between 40.9% and 32.4% for Method A and between 41.2% and 28.5% for Method B because the spleen volume is increased. The varying threshold edge detection technique described in this paper can be implemented successfully in the clinical setting.

Reference values for red cell survival times.

The first purpose of this investigation was to investigate in 35 young normal male subjects the use of the Dornhorst function and the weighted-mean method to calculate reference values for mean red cell survival time with and without correction for elution of 51Cr. We compared survival times calculated with the Dornhorst and weighted-mean methods with survival time estimated with linear or exponential models. Two methods to correct for elution of 51Cr from red cells were investigated. For the first method, correction factors were generated using the Dornhorst function fitted to mean survival curves obtained from the normal subjects. In the second method, the new Dornhorst rate constant method, the survival time, corrected for elution of 51Cr, was directly calculated from the experimental survival curve without applying correction factors. Correction for elution using the Dornhorst rate constant method was not successful and resulted in nonphysiologic values. The 95% confidence range of red cell survival time for reference subjects without correction for 51Cr elution was 37-74 days for the weighted-mean method and 37 to 73 days for the Dornhorst method. The 95% confidence range for normal subjects when the survival curves were corrected for elution was 47-179 days for the Dornhorst method and 58-161 days for the weighted-mean method. The poor results obtained with the Dornhorst rate constant method and the large 95% confidence range were due to the rapid and large variation in elution rate of 51Cr from red cells.

[A comparison of three different techniques for measuring glomerular filtration rate]. / 'n Vergelyking van drie verskillende tegnieke vir die berekening van glomerulêre filtrasiespoed.

The clearance of inulin, creatinine and radioactive tracers from the blood may be used to measure glomerular filtration rate (GFR). These techniques, however, are usually invasive and time-consuming. Although the clearance of a radioactive tracer is usually applied in nuclear medicine for the determination of GFR, it is also possible to convert the concentration of the tracer in the kidneys to absolute GFR by means of a regression equation. As this new technique is much faster, we have compared it with the conventional technique. A good correlation was found with the standard radionuclide techniques (r = 0.91), but the reference method was under-estimated on the average by 14 ml/min. The new regression equation derived in our clinic will ensure future accurate GFR measurements within 6 minutes.

Detecting asymptomatic coronary artery disease using routine exercise testing and exercise thallium scintigraphy in patients with atherosclerotic vascular disease.

ECG-monitored exercise testing has been proposed as a relatively inexpensive and effective means of screening for asymptomatic coronary artery disease in patients presenting for peripheral vascular surgery. Despite the fact that exercise thallium scintigraphy is also dependent on the patient's ability to exercise, using this test in conjunction with ECG-monitored exercise testing may enhance sensitivity and specificity of non-invasive evaluation. Thirty-two patients were subjected to ECG-monitored exercise testing, exercise thallium scintigraphy and coronary angiography. The sensitivity of ECG-monitored exercise testing for detecting coronary artery disease was calculated at 81.8% and the specificity at 87.5%, while the figures for exercise thallium scintigraphy were 73.1% and 33.3% respectively. Using these two methods in combination yielded a predictive accuracy of 90.6%. The only advantage of exercise thallium scintigraphy over exercise ECG appears to be in patients in whom the latter test could not be interpreted or was non-diagnostic.

A comparison of the clinical relevance of thallium-201 and technetium-99m-methoxyisobutyl-isonitrile for the evaluation of myocardial blood flow.

Thallium-201 is at present the radiotracer of choice for the clinical evaluation of myocardial blood flow. Although different technetium-99m-isonitrile agents have been synthesised recently, only 99mTc-methoxyisobutyl-isonitrile (99mTc-MIBI) has proved to hold promise for clinical implementation. The myocardial distribution of 201Tl and 99mTc-MIBI was compared in a group of 20 patients, who underwent both 201Tl single photon emission computed tomography and 99mTc-MIBI study as well as coronary angiography. The sensitivity for predicting a lesion ranged from 25% to 88% in different areas of the heart and was comparable for the two radiopharmaceuticals. The specificity was greater than 80% for all regions except the inferior region where a specificity of 58% obtained by 99mTc-MIBI was better than the low specificity of 17% obtained with 201Tl (P less than 0.008).

Left ventricular myxoma. A case report.

A 27-year-old woman with a systolic ejection murmur caused by a left ventricular myxoma is described. The diagnosis of this potential fatal condition was made by echocardiography. The clinical differences between atrial and left ventricular myxoma are discussed.

99mTc ethoxy methylpropyl isonitrile: a radioactive tracer for myocardial perfusion imaging.

The initial experience with a new 99mTc labelled myocardial perfusion agent, ethoxy methylpropyl isonitrile (EMI), is described in the primate as model. Rapid biliary clearance of EMI ensures low radionuclide concentration in the liver and lungs after 60 min. Adequate visualization of the myocardium is therefore possible. Heart-to-lung and heart-to-liver ratios of 1.52 and 2.45 respectively were obtained. EMI is an efficient imaging agent to evaluate myocardial ischemia and infarction.

Daily serial evaluation of left ventricular function with equilibrium radionuclide ventriculography following thrombolysis during acute myocardial infarction.

The changes in ventricular function after reperfusion by coronary thrombolysis are important when deciding about further definitive treatment necessary to ensure long-term vessel patency. The purpose of this study was to evaluate the early changes in left ventricular function after reperfusion. Left ventricular function was serially evaluated for 10 days in a group of 18 patients receiving intracoronary thrombolytic therapy for an acute myocardial infarction. Comparison of the global ventricular function in the successfully and unsuccessfully reperfused groups of patients showed significantly better function in the successful group than the unsuccessful group after the first day, which was maintained for the entire study period. Global and regional ventricular function in the successfully reperfused patients showed significant early improvement during the initial 72 h with maintenance of this improvement for the study period of 10 days. In the patients in whom reperfusion was unsuccessful, regional ventricular function showed no change, while the global function declined from day 5 to day 8 of the study period. This study then confirms the significant improvement in ventricular function after successful reperfusion. The time course pattern of the change in ventricular function indicates that the most significant improvement occurs within the first 72 h after reperfusion. These changes are similar to those previously reported in experimental animals.