Production of radioactive quality assurance phantoms using a standard inkjet printer.

This note proposes the use of a standard inkjet printer to produce radioactive (99m)Tc phantoms that can be used for routine quality control of gamma cameras. The amount of activity that will be deposited on paper per unit area was predicted and compared to the measured activity. The uniformity of the printouts was compared to the uniformity obtained with a standard (57)Co flood source. A scintillation detector connected to a multi-channel analyzer was used to evaluate the uniformity of the printout independently from the gamma camera. Joining two A4 size printed phantoms to create larger sources was evaluated. The spatial resolution obtained with printed sources was compared to that obtained using standard line source techniques. The results indicated that the uniformity of the printed phantoms compared well with those obtained with the (57)Co flood source (integral uniformity 2.29% (printed source) and 2.10% ((57)Co flood source)). There was no difference in the resolution measurements obtained with the printed sources and those obtained with the standard methods. This study demonstrates that affordable phantoms can easily be created to evaluate system uniformity and resolution in any department where a standard PC and inkjet printer are available.

The channel ratio method of scatter correction for radionuclide image quantitation.

The accuracy of quantitation of radionuclide distributions in human tissue with the scintillation camera is decreased by attenuation and scatter of photons. If scatter correction is applied satisfactorily, narrow beam attenuation can be applied. In this article, a scatter correction technique, the channel ratio (CR) method, is introduced. The CR scatter correction method is proposed for quantitation of the radionuclide distribution in organs. The improvement in the geometrical resolution was measured and examples of clinical images are presented. In this method, the change in the ratio of counts from two symmetrical adjacent energy windows straddling the energy photopeak was used to eliminate the contribution of scattered photons during imaging with 99mTc. The theory and methods for the empirical affirmation are described. To apply the CR scatter correction method, two constants, the ratio of primary photons G and the ratio of scattered photons H in the same windows, were determined. Different sized sources in varying depths of water were imaged. When the source activities were quantified after scatter correction with the CR method, the measurements ranged from 96%-108% in comparison to the reference value in 100 mm water. The scatter fraction increased from 0.20 in 10 mm water to 1.44 in 200 mm water. The geometrical resolution expressed as full width at tenth maximum in 150 mm water improved by 30.4% and was restored to the value of the geometrical resolution in air. The CR scatter correction method is a simple method to correct for scatter in order to facilitate accurate quantitation of the radionuclide distribution during imaging with a scintillation camera.

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.

Evaluation of left ventricular contractility indexes for the detection of symptomatic and silent myocardial ischemia.

This study evaluated the role of left ventricular (LV) ejection fraction and systolic blood pressure (BP) to end-systolic volume ratio to detect symptomatic and silent myocardial ischemia. The sensitivity and diagnostic accuracy of these contractility indexes were compared with angina and ST depression during exercise. Thirty consecutive patients referred for chest pain performed symptom-limited bicycle exercise and had coronary angiography within 3 months. Twenty-two had angiographically significant coronary artery disease and 8 had normal coronary anatomy. Systolic BP was measured by sphygmomanometry; LV ejection fraction and end-systolic volume were obtained by nuclear ventriculography. Normal values for contractility indexes were defined as LV ejection fraction greater than 52% at rest and increment of greater than or equal to 5% during exercise, and systolic BP to end-systolic volume ratio greater than 2.2 mm Hg/ml at rest and greater than 3.0 mm Hg/ml during exercise. The sensitivity of systolic BP to end-systolic volume ratio to identify patients with coronary artery disease at rest was 71 vs 33% for LV ejection fraction. During exercise, each contractility index had a sensitivity of 95% and there was a combined sensitivity of 100%. This compares with 71% for ST depression and 48% for exercise-induced angina. Thus, 52% had no angina and 36% of them were also silent by electrocardiography. Among the patients with symptomatic ischemia, 20% had no ST-segment depression. Measurement of contractility indexes enhanced the detection of silent myocardial ischemia and provided information on LV function vital to prognosis and management of patients with coronary artery disease.

The effects of different correction techniques on absolute volume determination with SPECT using a threshold edge detection method.

Quantitation of planar radionuclide images is hampered by structures containing radioactivity which overlie or underlie the organ of interest. The introduction of single photon emission computerized tomography (SPECT) overcame this problem to a large extent and enhanced the contrast of the images. Attenuation of photons, however, degrades the resultant SPECT images and correction methods for photon absorption and scatter were subsequently proposed. The different correction methods have variable effects on the reconstructed images. If threshold techniques are used to quantitate organ volume, i.e., combining pixels with the same percentage of the maximum pixel count in the volume, the selected threshold values which give the most accurate volume determination, will be affected by the specific correction method used. In this study, the effect of various SPECT image correction methods on threshold was investigated. A thorax phantom containing volumes ranging from 30 to 1200 ml was used. Threshold values varying from 45.6% (210 ml without any correction) to 23.7% (1200 ml with a combination of scatter subtraction and attenuation correction) were used to produce correct quantitation when different methods were investigated. A negative correlation was found between threshold and volume. This reduction in threshold was most prominent when scatter and attenuation correction were combined. This study shows that correction methods for attenuation of photons influence the threshold value for volume quantitation and the use of a constant threshold value could lead to underestimation of larger volumes.

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.

A Monte Carlo evaluation of the channel ratio scatter correction method.

Several methods exist to eliminate the contribution of scattered photons during imaging. One of these, the channel ratio (CR) scatter correction technique, uses the change in the ratio of counts from two symmetrical adjacent energy windows straddling the energy photopeak. The accuracy of the results depends upon the assumption that the ratio of the scatter components in the two windows (H value) is constant and is independent of the relative size of the scatter contribution. In this study a Monte Carlo simulation was used to investigate the behaviour of the scatter component for different source sizes at different depths. Four disc sources containing a 99Tcm solution were simulated at different depths as imaged with a scintillation camera. Two 10% energy windows with 5% offsets to either side of the 140 keV photopeak of 99Tcm were used. The ratio of the scattered counts in the lower energy window to the scattered counts in the upper window (true H value) was determined from the simulation for each source at every depth. Since it is impossible to measure the true H value at different organ depths during a clinical study, the use of an average H value was considered. Scatter correction was applied to the images simulated at the various depths in water. The geometric mean was calculated and attenuation correction performed assuming mono-exponential attenuation. For quantitation purposes the corrected counts were expressed in terms of a references source. The choice of the reference source yielding the best quantitative results was also investigated. Results of this Monte Carlo simulation study show that although the true H value depends on both source size and depth of the source in the scattering medium, the CR scatter correction technique can be applied successfully when an average H value is used.

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)

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.

Persistent left superior vena cava detected with radionuclide angiocardiography.

A 28-year-old man presented with paresthesias, fatigue, central cyanosis, and erythrocytosis. A first pass flow study with Tc-99m as free pertechnetate was done, among other tests, to exclude a central shunt when a persistent left superior vena cava was incidentally detected. The value of radionuclide angiocardiography to examine the central circulation noninvasively was again illustrated in this case.

Use of a personal computer for fast acquisition of cardiovascular data over an extended period.

This paper describes data collection during open chest cardiovascular research based on an IBM compatible personal computer. Data from eight analogue data channels are collected at a rate of 500 Hz per channel for a period of more than 40 sec per run. General analysis functions include the integration of the data obtained from any channel as well as an exponential curve fitting routine. Special functions are available for the calculation of cardiac parameters. This includes the automatic determination of end-diastole and end-systole, as well as maximum and minimum values of all curves for both the systolic and diastolic phases of contraction.

Evaluation of an uncollimated printed paper transmission source used under scatter limiting conditions.

Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources. The scatter contribution to the uncollimated (99m)Tc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images. Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances ≥ 60 cm; phantom source distances ≥ 40 cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168 cm⁻¹ vs. 0.171 cm⁻¹). The full widths at half maxima differed by less than 0.9 mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source. An uncollimated transmission source (detector source distance ≥ 60 cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging.

A comparison of the acute hemodynamic effects of nifedipine and nisoldipine in patients with ischemic reduced left ventricular function.

Nisoldipine (BAY k 5552) like nifedipine, is a dihidropyridine compound with strong calcium blocking activity. The purpose of this study was to measure and compare the absolute hemodynamic effects of these two drugs before and at 30 min, 60 min and 120 min after oral intake in 20 ischemic heart disease patients with radionuclide gated cardiac scintigraphy. No significant change was seen in end diastolic volume index with either of the drugs. With nifedipine the stroke volume index (SVI) increased significantly from the basal value at 30 min (P = 0.004) and 60 min (P = 0.034) yet not significantly at 120 min. The same trend was seen in left ventricular ejection fraction (LVEF) with significant increases at 30 min (P = 0.02) and 60 min (P = 0.025) yet not at 120 min. The cardiac index increased significantly at 30 min (P = 0.001), 60 min (P = 0.002) and 120 min (P = 0.025) but the latter value was significantly lower than the 30 min value indicating the maximal effect had already passed. With nisoldipine the SVI increased significantly at 60 min (P = 0.004) and 120 min (P = 0.001) but not at 30 min. These changes were again reflected by a significant increase in LVEF at 60 min (P = 0.021) and 120 min (P = 0.002) without significant increase at 30 min. The increase in CI was highly significant at 60 min (P = 0.003) and 120 min (P = 0.001) without significant change at 30 min. Nisoldipine proved to be a potent calcium antagonist with slower onset and longer duration of action than nifedipine.

Radionuclide determination of absolute LV volumes: interstudy, interobserver and intraobserver variances.

The results of 22 absolute left ventricular volume (LVV) determinations by a radionuclide (RN) method are compared to the results obtained by contrast ventriculography (CV). Another 10 patients were analysed in order to evaluate the interstudy, interobserver and intraobserver variances. Good correlation was shown between the RN and CV measurements of the end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV) and ejection fraction (EF), but the RN method overestimates the EDV and ESV. The EF was underestimated, but no difference could be shown for the SV. On the inter- and intraobserver levels, regression analysis yielded excellent correlation (r greater than 0.99 in all cases) with no statistically significant difference (P less than 0.05). The interstudy variance was minimal as indicated by regression analysis (r greater than 0.87) and no statistically significant difference (P less than 0.05) could be shown between studies. The results indicate that the RN method of LVV determination can be used in intervention studies over a limited period.

[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.

Variation in left ventricular ejection fraction determination at rest and during exercise.

The results of multi-gated blood pool imaging (MBPI) for determination of left ventricular ejection fraction (LVEF) in 48 patients at rest and during exercise were analysed in order to evaluate observer variance and interstudy variance. Twenty-three MBPI studies carried out with the patient at rest and 37 studies carried out during graded ergometer exercise were analysed by two independent observers in order to determine intra- and inter-observer variance. On the intra-observer level regression analysis yielded excellent correlation between rest and exercise studies (r = 0,998 at rest, r = 0,964 during exercise), and showed no statistically significant difference (P less than 0,01); this was also true of the inter-observer measurements (r = 0,999 at rest, r = 0,988 during exercise). In order to evaluate interstudy variance, MBPI was repeated in 15 patients at rest. Interstudy variation of the LVEF was minimal as indicated by regression analysis (r = 0,98), and showed no statistically significant difference (P less than 0,01). During the repeat study a mean increase in the LVEF of 2,1% was obtained, but this difference was not statistically significant.

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.

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).

The effects of nisoldipine on left ventricular filling rate in patients with ischemic heart disease measured with radionuclide gated blood pool scintigraphy.

Nisoldipine is a newly developed calcium channel blocker with outstanding vasodilatory properties especially with regard to the coronary arteries. Thus it may find wide-spread application as a therapeutic agent in various ischemic heart disease syndromes. The purpose of this study was to evaluate the effect of nisoldipine on the diastolic function of the left ventricle (LV) in the clinical situation. A patient group on nisoldipine treatment was compared to a control group. In the nisoldipine group a maximum decrease of 17 mmHg in the mean systolic blood pressure with an increase in the mean peak ejection rate (0.78 EDV/s) and peak filling rate (0.52 EDV/s) were observed. Mean LV ejection fraction increased by 6.4% and the time to peak filling rate decreased by 36.5 ms. After eight weeks of treatment the acute effects of nisoldipine were similar to the previous study. Nisoldipine therefore tends to improve both the diastolic and systolic function of the left ventricle.

The imaging of myocardial perfusion with 81mKr during coronary arteriography.

The use of 81mKr was investigated for imaging myocardial perfusion during coronary arteriography using conventional catheters. When the significance of stenosis judged by arteriography is unclear, the effect on tissue perfusion can be established and the contribution to collateral flow by each artery separately evaluated. The distribution of 81mKr, due to its 13-s half-life, represents regional blood flow. In order to evaluate interventions, studies can be repeated at a low radiation risk to patients. A sterile pyrogen-free 81Rb-81Kr generator was developed. With slow infusion, inadequate mixing and streaming takes place due to laminar flow in coronary arteries. Fast intermittent 3-ml 81Kr-dextrose bolus injections convincingly eliminated streaming artefacts. Imaging was performed in 13 patients with a mobile scintillation camera and digital imaging system. Blood flow was calculated using the inert gas washout technique. There was good correlation (r = 0.91) between coronary blood flow determinations using 81mKr and 133Xe respectively. The perfusion images correlated well with the coronary angiograms. Total coronary arterial occlusions as demonstrated by arteriography were all shown as perfusion defects during rest. During atrial pacing myocardial flow was increased two-fold in normal coronary arteries and to a lesser extent in arteries with significant disease. The most critical lesion in a branch of a left coronary artery leads to a redistribution of perfusion during pacing.