Biomedical subjects

A van Lingen

Publications and source records attributed to A van Lingen.

At least 55 records · Page 3Linked to original sources

PubMed1996

Comparison of myocardial uptake of fluorine-18-fluorodeoxyglucose imaged with PET and SPECT in dyssynergic myocardium.

UNLABELLED: PET with 18F-fluorodeoxyglucose (FDG) can detect viable myocardium and predict functional recovery after revascularization. The use of PET for clinical routine, however, is limited. Recently, imaging FDG with SPECT was proposed. The aim of this study was to compare the diagnostic value of FDG-PET and FDG-SPECT in the detection of viable myocardium in segments with abnormal wall motion. METHODS: Twenty patients with previous myocardial infarction were studied. All underwent FDG-PET and FDG-SPECT during hyperinsulinemic glucose clamping. Regional perfusion was assessed with 13N-ammonia PET and early resting 201TI- SPECT. Regional wall motion was assessed with two-dimensional echocardiography. The agreement between FDG/13N-ammonia PET and FDG/201TISPECT to detect viability in dyssynergic myocardium was 76%. On a patient basis, PET and SPECT yielded comparable results in 17 of 20 patients. In a subgroup of patients with LVEF < or = 35% (n = 12), all PET and SPECT viability data were identical. CONCLUSION: This study shows a good correlation between the detection of viability in dyssynergic myocardium with FDG/13N-ammonia PET and FDG/201TI SPECT, both on a segmental and patient basis.

Ammonia↗

PubMed1995

Influence of high and low plasma insulin levels on the uptake of fluorine-18 fluorodeoxyglucose in myocardium and femoral muscle, assessed by planar imaging.

The aim of this study was to optimize the metabolic conditions for planar myocardial fluorine-18 fluorodeoxyglucose (FDG) imaging. The effects of high and low insulin levels during euglycaemic clamping on myocardial and femoral muscle FDG uptake were compared since insulin plays a major role in glucose metabolism. FDG uptake in 11 patients was studied using planar scintigraphy. Patients were studied twice: in the low-dose insulin protocol (LDI), insulin was infused at a rate of 20 mU/kg per hour, starting 1 h before FDG administration, while in the high-dose insulin protocol (HDI) it was infused at a rate of 100 mU/kg per hour. Glucose infusion rate was adjusted according to frequently determined blood glucose levels. Somatostatin was infused to block endogenous insulin release. Planar images were obtained from the thorax region and femoral muscles. Regions of interest were drawn over normal and abnormal myocardial areas (based on angiographic and thallium-201 data) and over lung, liver and muscle areas. After clamping, insulin levels during LDI and HDI at t = 60 were 30.6 +/- 13.3 and 129.6 +/- 30.5 mU/l respectively (P < 0.0001). Femoral muscle uptake was significantly higher during HDI (P < 0.001). Uptake in normal and abnormal myocardial areas did not differ between the two protocols. Heart/lung ratios (NS) and heart/liver ratios (P < 0.05) increased during HDI. It may be concluded that planar FDG imaging is influenced by plasma insulin levels. The euglycaemic hyperinsulinaemic clamp technique, although more demanding, gives an adjustable metabolic steady state without significantly altering the FDG uptake patterns in normal and abnormal myocardial regions. The image quality of planar FDG images improves due to lower background uptake of FDG during clamping with high plasma insulin levels.

Case-Control Studies↗

PubMed1995

Relation between myocardial uptake of thallium-201 chloride and fluorine-18 fluorodeoxyglucose imaged with single-photon emission tomography in normal individuals.

Recently, we have demonstrated the feasibility of imaging myocardial uptake of fluorine-18 fluorodeoxyglucose (FDG) with single-photon emission tomography (SPET) using a specially designed collimator. Thallium-201 was used to determine distribution of perfusion for comparison with FDG uptake. However, regional 201Tl and FDG activities may be different, based on differences in tracer attenuation and the use of different collimators. To study the relation between tracer activities imaged with SPET, nine healthy individuals underwent resting 201Tl SPET and FDG SPET during a hyperinsulinaemic euglycaemic clamp. The SPET data were analysed semiquantitatively, using circumferential profiles. Mean profiles of midventricular short-axis slices showed no significant difference between 201Tl and FDG activity. Regional fluctuations were similar for FDG and 201Tl; the highest tracer activities were observed in the lateral wall and the lowest activities in the septum. Finally, pooled data (n = 1620 segmental activities) in nine individuals showed a linear correlation (P < 0.0001) between 201Tl and FDG activity: FDG = 0.76 201Tl + 0.23 (r = 0.70). These data demonstrate the absence of major differences between regional 201Tl and FDG activity in normal myocardium, suggesting that no separate 201Tl and FDG SPET reference values are needed for comparison with patient studies.

Adult↗

PubMed1995

Radiotoxicity of 67-gallium on myeloid leukemic blasts.

Promising clinical results are obtained with radiolabeled antibodies in leukemia patients. 67Gallium (67Ga) is a radionuclide that accumulates in many malignant tissues without need for a monoclonal antibody. For this reason, the use of 67Ga as a therapeutic agent is appealing. In the present we study, we report data about the radiotoxicity of 67Ga on peripheral blast cells of 23 patients with acute myelogenous leukemia (AML) in vitro. Isolated blast cells were incubated for 4 days with 0.74 MBq/ml (20 microCi/ml), 1.48 MBq/ml (40 microCi/ml) or 2.96 MBq/ml (80 microCi/ml) 67Ga. Compared with non-irradiated control cells proliferation during incubation was almost abolished. Clonogenic survival was measured by a colony forming unit assay (CFU-assay). In 13 of the 23 patients (56%) sufficient colony growth was observed for evaluation. The mean clonogenic survival of blasts after incubation with 0.74 MBq/ml and 2.96 MBq/ml 67Ga was 22.5, 11.3 and 3.5%, respectively. In some cases colony growth was completely abolished after incubation with only 0.74 MBq/ml 67Ga. No correlation was found between cellular 67Ga-uptake, (micro)dosimetry and transferrin receptor density (CD-71) via which 67Ga enters the cell. In vitro the blasts received a dose of > 10 Gy in 9 of the 2.96 MBq/ml, in 3 of the 1.48 MBq/ml and in 2 of the 0.74 MBq/ml incubations. In one patient, even a radiation dose > 40 Gy was reached. Low dose rate irradiation is known to arrest cells in G2/M-phase of the cell cycle, but no such arrest was observed during incubation with 67Ga. Thus, 67Ga induces clonogenic cell death in leukemic blasts. Cellular uptake of 67Ga in vitro varies between patients and can be very high in some patients. The easy availability, low costs and absence of immunological problems warrant further investigation of the therapeutic potential of 67Ga in refractory or relapsed AML patients.

Acute Disease↗

PubMed1995

Myocardial F-18 fluorodeoxyglucose imaging by SPECT.

F-18 fluorodeoxyglucose (FDG) in combination with positron emission tomography (PET) is used in patients with coronary artery disease to detect viable myocardium. It was shown that FDG PET is highly accurate in predicting reversibility of cardiac function after revascularization when viable tissue is present. Because PET centers are not widely available, the clinical use of FDG is limited. The authors have shown in another study that imaging 511 keV with planar scintigraphy and a special collimator is feasible. Furthermore, they have studied myocardial FDG uptake in normal volunteers and in patients with coronary artery disease using SPECT. Recently, they have studied the value of FDG SPECT to predict recovery of contractile function before revascularization in patients undergoing bypass surgery. It appears that the FDG SPECT approach is feasible and can predict reversibility of wall motion abnormalities. Further studies are needed to compare FDG SPECT with other techniques for the detection of viable myocardium.

Coronary Disease↗

PubMed1995

Additional weight-bearing during exercise is more important than duration of exercise for anabolic stimulus of bone: a study of running exercise in female rats.

Mechanical loading is necessary for maintenance of skeletal integrity, but the most effective type, intensity, and duration of exercise are not known. In vivo experiments have indicated that the strain generated by the stimulus is more important than the duration of the stimulus. To elucidate this question, we studied 5-month-old female Wistar rats exercised on a motor-driven exercise belt for 17 weeks, 5 days per week (average velocity 20 m/min). Group 1 served as controls, group 2 was trained for 30 min, group 3 was trained for 30 min with a 50-g backpack, and group 4 was trained for 15 min with a 50-g backpack. Total body bone mineral content (BMC), bone mass of the lower extremities (LEBMC), total body lean soft-tissue mass (LSTM), and total body fat-tissue mass (FTM) were measured by dual-energy absorptiometry (DXA) at 0, 6, and 17 weeks. The BMC increased more in group 4 than in controls (15% vs. 8%, p < 0.03). In the other two intervention groups, no significant increases of total body BMC occurred compared with controls, although a trend was observed (12%). The LEBMC increased significantly in all exercising groups after 17 weeks, being 16% in group 2, 15% in group 3, and 20% in group 4, compared with 6% in controls (p < 0.05). The increase in LSTM after 6 weeks was most pronounced in group 3, at 20%, compared with 10% in the control group (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗

PubMed1995

Feasibility of planar fluorine-18-FDG imaging after recent myocardial infarction to assess myocardial viability.

UNLABELLED: The aim of this study was to define the clinical feasibility of planar myocardial 18F-fluorodeoxyglucose (FDG) imaging and to assess the relation between 201Tl, FDG and left ventricular function early after myocardial infarction. METHODS: Fifty-one patients were studied 5 +/- 2 days after infarction. Scintigraphic images were visually and quantitatively analyzed using a circumferential profiles technique. FDG uptake was normalized to the area with maximal 201Tl uptake. Scintigraphic data were compared with left ventricular wall motion as assessed by ventriculography in 22 patients. Relative regional 201Tl uptake was categorized as normal (> or = 75% of peak activity), moderately reduced (50%-75%) or severely reduced (< 50%). These tracer defects were considered viable if FDG uptake exceeded 201Tl uptake by > or = 20% and/or if FDG uptake was normal (> or = 75%). All regions with FDG uptake 20% less than 201Tl uptake were considered nonviable. RESULTS: Four hundred forty-one myocardial regions were analyzed; 200 showed normal 201Tl uptake, 241 had reduced uptake, 191 had moderately reduced 201Tl uptake and 50 regions had severely reduced uptake. Viability for moderately and severely reduced regions was observed in 62% and 48%, respectively. A concordance between flow and metabolism was observed in 38% and 52%, respectively. CONCLUSION: Myocardial FDG imaging is feasible with standard gamma camera systems and enables the identification of regions with preserved glucose metabolism in patients shortly after infarction.

Coronary Angiography↗

PubMed1995

Biodistribution of radiolabeled monoclonal antibody E48 IgG and F(ab')2 in patients with head and neck cancer.

Biodistribution and pharmacokinetics of radiolabeled mAb E48 IgG and E48 F(ab')2 were analyzed and compared in 39 patients with histologically proven squamous cell carcinoma of the head and neck who were included in a radioimmunoscintigraphy study and underwent surgery 44 h after injection. Three groups of patients were distinguished: group 1 (n = 19) received technetium-99m (99mTc)-labeled E48 F(ab')2, group 2 (n = 9) received 99mTc-labeled E48 IgG, and group 3 (n = 11) received 99mTc- and 131I-labeled E48 IgG as well as 125I-labeled F(ab')2. Two patients in group 1 and four patients in group 3 received a high mAb dose (10-50 mg), while all other patients received a low mAb dose (1-4 mg). From all patients in groups 2 and 3 biopsies from the surgical specimen were obtained 44 h postinjection. Tumor uptake of 99mTc-labeled E48 IgG was high, ranging from 0.007 to 0.082% of the injected dose/g, with a mean of 0.031 +/- 0.020% of the injected dose/g. The mean tumor:nontumor ratio of this conjugate was 2.8 for mucosa, 4.6 for bone marrow aspirate, 4.1 for blood, 20.3 for fat, and 21.0 for muscle. Activity uptake in tumor positive lymph nodes was 4.7 times higher as compared to negative lymph nodes. Sixteen h postinjection radioimmunoscintigraphy revealed activity uptake in the primary tumor, lymph node metastases, oral cavity, and adrenal glands. Using regions of interest, the uptake in the adrenal glands was estimated to be 0.050% of the injected dose/g. If a high mAb dose was used, no adrenal glands were visualized and the uptake in the oral cavity was clearly diminished, while the tumor uptake and tumor:nontumor ratios were increased. The mean elimination half-lifes t1/2 alpha and t1/2 in plasma were: for E48 IgG (n = 20) 6.6 +/- 2.6 and 54.1 +/- 24.3 h and for E48 F(ab')2 (n = 19) 2.3 +/- 0.4 and 19.9 +/- 4.6 h, respectively. Tumor uptake of 131I-labeled E48 IgG was 49% higher than of 125I-labeled F(ab')2. For most tissues except normal oral mucosa, tumor:nontumor ratios were slightly higher for F(ab')2 than for IgG. The present study shows that mAb E48 accumulates selectively and to a high level in head and neck squamous cell carcinoma. Although no definite conclusions can be drawn as to which mAb form is more suitable, IgG or F(ab')2, mAb E48 seems to have potential for radioimmunotherapy in head and neck squamous cell carcinoma patients.

Adrenal Glands↗

PubMed1994

A dosimetric model for intrathecal treatment with 131I and 67Ga.

PURPOSE: Calculations were performed of absorbed dose distributions of the beta-emitter 131I and the Auger emitter 67Ga for intrathecal administration. METHODS AND MATERIALS: The proposed dosimetric model accounts for the macroscopic distribution of the activity, by means of a Medical Internal Radiation Dose Committee approach, and for the microscopic distribution of activity, by means of a point kernel technique. This point kernel approach was used in combination with a distance histogram technique, to study in more detail the absorbed dose distribution in the cerebro-spinal fluid, in the surface of the central nervous system, and in tumor sites. We simulated decreased uptake, as well as highly selective uptake in free-floating tumor cells and in meningeal lesions (1-16 cells thick). RESULTS: In case of limited access to lesions adherent to the pia mater, the beta-emitter 131I provides crossfire from the CSF, resulting in a higher absorbed dose (Gy/MBq) in these lesions as compared with the Auger emitter 67Ga. In case of increasing radionuclide uptake, the increment of the absorbed dose in the adherent lesions and the free floating cells from 67Ga is considerable because of the local deposition of energy by this radionuclide. CONCLUSIONS: The model might be useful to select the optimal emission characteristics of radionuclides applicable for intrathecal therapy, which is demonstrated in a comparison of the Auger emitter 67Ga and the beta-emitter 131I.

Gallium Radioisotopes↗

PubMed1994

Consequences of childhood-onset growth hormone deficiency for adult bone mass.

To assess the implications of prolonged growth hormone deficiency (GHD) for the acquisition and maintenance of bone mass, bone mineral density (BMD) was measured in 70 adult males (mean age 26.7 +/- 4.5 years) with childhood-onset GHD, 7.4 +/- 4.2 years after discontinuation of previous GH therapy. Because most of these patients were short (mean height 165.8 +/- 6.6 cm), the influence of body height on standard BMD measurements, conventionally reported as the areal density (BMDarea, expressed in g/cm2), was analyzed in a group of age-matched healthy males. In GHD patients, BMDarea was significantly reduced at the lumbar spine (Z score -1.59 +/- 1.08, p < 0.001) as well as at the nondominant hip (Z score -1.18 +/- 0.95, p < 0.001). The reduction in BMDarea was similar for patients with isolated GHD (N = 25) and those with combined deficiencies of GH and luteinizing hormone (N = 40). In patients and controls, BMDarea was positively correlated with body height, a relation that was attributed to skeletal size. Bone dimensions were significantly smaller in patients than in controls, and therefore it was hypothesized that the difference in areal density between patients and controls might be confounded by differences in bone size. Measured bone mineral content corrected for the estimated bone volume (BMDvolume, expressed in g/cm3) remained significantly reduced (Z score: lumbar spine, -0.90 +/- 1.08, p < 0.001; femoral neck, -0.74 +/- 1.00, p < 0.001), but the differences between GHD patients and controls were less than indicated by BMDarea (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Comparison of non-invasive approaches to red marrow dosimetry for radiolabelled monoclonal antibodies.

Red marrow is usually the dose-limiting organ during radioimmunotherapy. Several non-invasive approaches to calculate the red marrow dose have been proposed. We compared four approaches to analyse the differences in calculated red marrow doses. The data were obtained from immunoscintigraphy of two antibodies with different red marrow kinetics [iodine-131-16.88 IgM and indium-111-OV-TL-3 F(ab')2]. The approaches are based on, respectively, homogeneously distributed activity in the body, a red marrow-blood activity concentration ratio of 0.3, scintigraphic quantification, and a combination of the second and third approaches. This fourth approach may be more adequate because of its independence from the chosen antibody. In addition, the influence of activity accumulation in liver, kidneys or cancellous bone on red marrow dose was studied. The calculated red marrow dose varied between 0.14 and 0.42 mGy/MBq for 111In-OV-TL-3 and between 0.13 and 0.68 mGy/MBq for 131I-16.88. If the radiopharmaceutical shows high affinity for cancellous bone or another organ situated near the red marrow, the activity in these organs must be included in dose calculations. This study shows a large variation in calculated red marrow dose and selection of the definitive non-invasive approach awaits validation.

Bone Marrow↗

PubMed1993

Early response monitoring in malignant lymphoma using fluorine-18 fluorodeoxyglucose single-photon emission tomography.

Metabolic response monitoring early during chemotherapy may have a major impact on clinical management of patients with malignant lymphoma. In two patients with non-Hodgkin's lymphoma fluorine-18 fluorodeoxyglucose (18FDG) single-photon emission tomography (SPET) studies were performed during the first two chemotherapeutic cycles. Persisting uptake predicted treatment failure whereas a sharp reduction of 18FDG uptake was demonstrated in the case of a responsive tumour. Qualitative analysis of conventional 18FDG imaging may thus serve to identify patients with a non-responding tumour. The potential of this technique in the determination of the initial response remains to be established. Imaging with 18FDG and SPET appears promising as a more easily available methodology than 18FDG positron emission tomography.

Adult↗

PubMed1993

Feasibility of assessing regional myocardial uptake of 18F-fluorodeoxyglucose using single photon emission computed tomography.

Differentiation between viable myocardium and scar tissue in segments with abnormal contraction has important consequences in the clinical management of patients with coronary artery disease. Positron emission tomography (PET) can identify viable tissue using 18F-fluorodeoxyglucose (FDG). However, application of PET for daily routine is limited. In this study, FDG uptake was visualized with single photon emission computed tomography (SPECT) and compared with regional perfusion assessed with thallium-201 (201Tl) SPECT. The scintigraphic findings were related to regional wall motion determined with two-dimensional echocardiography. Patients (n = 9) with wall motion abnormalities underwent FDG SPECT and resting 201Tl SPECT. To control the metabolic status patients were studied with a hyperinsulinaemic euglycemic clamp during FDG SPECT. Analysis of reconstructed data was performed visually and semiquantitatively using circumferential profiles. High-quality images were obtained. Eight 201Tl defects showed concordantly decreased FDG uptake (metabolism-perfusion matches) indicating scarred tissue, whereas six regions of hypoperfusion demonstrated a relatively increased FDG uptake (mismatches), suggesting viable myocardium. Semiquantitative analysis confirmed visual findings. Mean 201Tl and FDG activities were not significantly different in matching defects. In mismatches the mean FDG activity was 81 +/- 11% vs 64 +/- 9% mean 201Tl activity (P < 0.0001). In four of six segments with increased FDG uptake, two-dimensional echo revealed hypokinesia. Seven of eight regions with a matching defect in contrast were akinetic. Thus, in the areas with a mismatch contractility was preserved. We conclude that FDG uptake can be visualized with SPECT. Furthermore, our preliminary observations suggest that this approach can identify viable tissue.

Adult↗

PubMed1993

Transvascular transport of 67Ga in the lungs after cardiopulmonary bypass surgery.

STUDY OBJECTIVE: To examine the effect of cardiac surgery with cardiopulmonary bypass (CPB) on pulmonary vascular permeability. DESIGN: A prospective, serial study. SETTING: Department of nuclear medicine and intensive care units of a university hospital. PATIENTS: Twelve consecutive patients were studied, before and immediately after elective cardiac surgery using CPB (group 1), and 4 consecutive, artificially ventilated patients with acute cardiogenic pulmonary edema (group 2). MEASUREMENTS AND RESULTS: The kinetics in blood and over both lungs were measured, using two mobile probes at the bedside, of intravenously injected 67Ga, assumed to bind to circulating transferrin, and in vitro 99mTc-labeled red blood cells to account for pulmonary blood volume. From data recorded in time (1 h), a pulmonary leak index (PLI), the time constant of transport of 67Ga from the intravascular to the extravascular space of the lung, was calculated and values for both lungs were averaged. In group 1, the PLI (.10(-3).min-1, mean +/- SD) was 8.2 +/- 3.7 before and 17.0 +/- 13.5 after CPB surgery (p < 0.01) and changes directly related to the duration of CPB. In four patients with a CPB duration > or = 120 min, the PLI, 31.1 +/- 16.3.10(-3).min-1, exceeded 2 SD plus mean preoperative PLI. Changes in PLI tended to relate inversely to changes in arterial WBC, which, in turn, inversely related to CPB duration. The PaO2/FIO2 ratio decreased and tended to relate inversely to PLI after surgery. No patient developed alveolar pulmonary edema on chest radiograph. In group 2, the PLI was 11.1 +/- 3.1.10(-3).min-1 (NS from group 1 preoperative PLI). CONCLUSIONS: Cardiopulmonary bypass induces a pulmonary vascular leak, as assessed by 67Ga kinetics using a bedside detection technique, in some cardiac surgery patients with prolonged CPB. This leak may reflect pulmonary vascular injury and increased permeability, following activation of leukocytes by CPB and subsequent pulmonary sequestration, rather than increased filtration through pressure factors. It may contribute to impaired gas exchange, even in the absence of manifest alveolar edema of the lungs, after surgery.

Acute Disease↗

PubMed1993

Early treatment response in malignant lymphoma, as determined by planar fluorine-18-fluorodeoxyglucose scintigraphy.

Clinical oncology needs flexible techniques for routine monitoring of treatment response. We therefore compared planar 18F-fluorodeoxyglucose (FDG) with a conventional gamma-camera and a special collimator to 67Ga scintigraphy in 26 patients with malignant lymphoma during chemotherapy. The scintigraphic appearance of involved sites was essentially the same with both tracers: in patients eventually achieving complete remission, tracer distribution had normalized after two courses; high uptake reflected treatment failure; faint uptake was associated with variable outcome. For (re)staging, 67Ga may be preferable (higher contrast). To document the initial response, we performed FDG scintigraphy during the first course (n = 11). Effective treatment sharply reduced metabolic tumor activity within days and prior to volume response, whereas abnormal uptake persisted in treatment failure. Planar FDG scintigraphy may be a tool to assess the potentially prognostic initial response rate, preventing over-treatment and allowing a timely switch to more aggressive therapy.

Deoxyglucose↗

PubMed1992

Radioimmunoscintigraphy of head and neck cancer using 99mTc-labeled monoclonal antibody E48 F(ab')2.

The diagnostic value of 99mTc-labeled monoclonal antibody E48 F(ab')2 (750 MBq, 1 mg) was evaluated in 10 patients with a histologically proven squamous cell carcinoma of the head and neck and with clinical evidence of cervical lymph node involvement. Preoperative findings on lymph node status obtained by radioimmunoscintigraphy (RIS), computerized tomography, magnetic resonance imaging, and palpation were defined per side (left and/or right side of the neck) as well as per lymph node level (I through V) and compared with the histopathological outcome of the neck dissection specimen. In 10 patients, all 8 known tumors at the primary site were detected by RIS. Furthermore, RIS was correct in 13 of 13 tumor involved neck sides and in 17 of 20 tumor involved lymph node levels. False-negative observations comprised 3 levels containing tumor deposits smaller than 1 cm in diameter, 2 of which were not detected by any other diagnostic modality. Palpation, computerized tomography, and magnetic resonance imaging were correct in, respectively, 13, 15, and 15 of the 20 tumor involved levels. There were 2 false-positive observations with monoclonal antibody E48 and 3 with palpation. No false-positive detections occurred with computerized tomography or magnetic resonance imaging. In two of the patients, RIS provided clinically important information which was not provided by any other diagnostic method. In one patient, recurrence of laryngeal carcinoma was established at the primary site after previous radiotherapy. In another patient, bilateral instead of unilateral lymph node involvement became apparent. These preliminary data indicate that radioimmunoscintigraphy with monoclonal antibody E48 may be helpful in the diagnosis of metastatic and recurrent head and neck cancer.

Adolescent↗

PubMed1992

Performance characteristics of a 511-keV collimator for imaging positron emitters with a standard gamma-camera.

Line-source experiments were conducted to assess the performance of a gamma-camera equipped with a specially designed 511-keV collimator for the planar imaging of positron emitters. The results were compared with the camera performance with routinely used collimators and radionuclides (thallium-201, technetium-99m and gallium-67). With positron emitters, scatter contributed less to the widening of the line spread function than with radionuclides emitting lower photon energies. These observations can be explained by the relative deterioration in the discrimination power of the gamma-camera to reject scattered radiation at low energies. Planar 511-keV imaging may provide relevant clinical information, as we showed by fluorodeoxyglucose studies in a patient with a myocardial infarction and in a patient with a malignant lymphoma. It is concluded that positron emitters can be effectively applied for planar imaging with the generally available gamma-cameras. This study implies that radiotracers developed for positron emission tomography may find a place in the practice of conventional nuclear medicine.

Adult↗

PubMed1992

Kinetics and dosimetry of iodine-131-labelled antibody fragments after local administration in patients with rectal cancer.

In 11 patients with rectal cancer, a mixture of F(ab')2 fragments of anti-carcinoembryonic antigen and anti-CA 19.9 labelled with a diagnostic dose of iodine-131 (3-10 MBq) was administered submucosally around the tumour. In this study, the local kinetics in and the dose to the rectal wall, the whole body kinetics and the effective dose equivalent are presented. The early disappearance of the activity from the injection spot was characterized by a T1/2 of 21 h. Initially, about 50% of the plasma activity was due to free 131I. After 4 h, the plasma activity was almost completely protein bound (86%). Maximum plasma activity was observed after the 2nd day. From 72 h p.i., the plasma activity decreased with a T1/2 of 53 h. In the first 24 h, 14% of the injected dose was excreted in the urine and within 4 days about half of the administered activity. The absorbed radiation dose to the rectal wall was estimated to be 0.2 Gy/MBq, presuming a 20 cm3 distribution volume. The dose to the bone marrow was 0.2 mGy/MBq or 0.4 mGy/MBq, assuming a homogeneous tracer distribution or equal blood and bone marrow activity concentrations, respectively. The effective dose equivalent is 1.9 mSv/MBq, mainly determined by the dose to the rectal wall and to a lesser extent by the dose to the remaining body. Postulating comparable kinetics, 123I- or 111In- or 99mTc-labelled fragments would result in 4-25-fold lower effective dose equivalents.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗