Quantitative comparison between 99mTc-HMPAO and 99mTc-ECD: measurement of arterial input and brain retention

This report describes a comparative study between technetium-99m ethyl cysteinate dimer (ECD) and ^99mTc-hexamethylpropylene amine oxime (HMPAO) in five neurological patients. The conversion kinetics of the tracers in the blood from forms capable of diffusion across the blood-brain barrier to non-diffusible forms were studied by arterial sampling and rapid octanol extraction. We observed that HMPAO has a faster conversion rate in the blood but that the fraction of the injected dose available for brain extraction is higher than in the case of ECD. Regional brain concentrations of the tracers were measured with single-photon emission tomography (SPET) 35 min and 60 min after the injection and remained stable within this interval. On the basis of the measurements of the arterial input and of SPET brain concentrations of the tracers, the regional steadystate influx constants (Ki in ml/min/g) were determined for several brain regions. In the grey matter the Ki values were (mean ± SD) 0.32 ± 0.03 and 0.35 ± 0.04 for HMPAO and ECD, respectively; in the white matter the values were 0.23 ± 0.01 and 0.23 ± 0.02, respectively. The Ki values of the two tracers in corresponding regions were closely correlated (P<0.001). The correspondence of the Ki values of ECD and HMPAO demonstrates that ECD can also be considered a tracer that may be used for quantitative measurements of brain perfusion. Correspondence to: A. Pupi     

In vitro assessment of cytotoxicity and labeling efficiency of 99mTc-HMPAO with stromal vascular fraction of adipose tissue

IntroductionNoninvasive radionuclide imaging of cells using technetium99m-hexamethylpropyleneamine oxime (^99mTc-HMPAO) is a potential diagnostic tool for several applications. Herein we aimed to evaluate the labeling efficiency and cellular toxicity of ^99mTc-HMPAO with Stromal Vascular Fraction (SVF) of adipose tissue to develop a process tool for theranostic purposes, in particular imaging cardiac stem cell therapy.MethodsTen million cells of SVF were labeled with ^99mTc-HMPAO complex and excess radiolabel was cleared off through washing in PBS. The labeling efficiency of ^99mTc-HMPAO was detected in labeled cells and their subsequent supernatant wash using isotope dose calibrator and gamma camera. The cytotoxicity was assessed for the comparative reactive oxygen species (ROS) by H₂DCFDDA, apoptotic events by annexin-V and TUNEL assay and mitochondrial potential by JC-1.ResultsAn encouraging labeling efficiency of 33% was observed with ^99mTc-HMPAO complex. The radionuclide labeling of SVF demonstrated significant safety profile as evaluated by apoptotic assays.Conclusion^99mTc-HMPAO labeling efficiency of 33% of total SV fraction would produce sufficient radioactive signals that would enable for in vivo tracking of cells by SPECT-CT. The radionuclide did not demonstrate any significant impact on the structural or functional organization of the labeled cells. Our study indicates that SVF can be safely labeled with ^99mTc-HMPAO without adverse cytotoxic events and for its potential role in imaging cardiac stem cell therapy.     

Accumulation of99mTc-HMPAO and99mTc-ECD in rodent and human breast tumor cell linesin vitro

The accumulation of^99mTc-HMPAO and^99mTc-ECD was studied in rat (MatB) and human (MCF-7) breast tumor cell linesin vitro as a function of incubation time. The general pattern was the same for both tracers and both cell lines: the tracer rapidly and extensively accumulated in the cells but a plateau was reached in 15–30 minutes. Accumulation of HMPAO was higher than that of ECD, did not show a difference between rat and human cells, and correction of HMPAO data for intracellular sequestration and extracellular metabolism resulted in a linear increase in accumulation with time. In contrast, accumulation of ECD was ～ 2-fold higher in human cells than in rat cells but after correction for sequestration and metabolism a plateau remained. These experiments show differences between HMPAO and ECD in their accumulation and retention in breast cancer cellsin vitro and support that the need for further work on the potential clinical role for HMPAO in tumor characterization.     

A novel potential application for 99mTc-HMPAO: endothelial cell labeling for in vitro investigation of cell-biomaterial interactions.

Good adherence of endothelial cells (ECs) seeded on vascular prostheses and cell retention under flow conditions are important factors to consider in the use of functionalized prostheses in vascular surgery. Because 111In-oxine radiolabeling presents disadvantages, we wondered whether, because of its well-known physical properties, 99mTc-hexamethyl propyleneamine oxime (HMPAO or exametazime) could be used. Methods: The cytotoxicity of unlabeled HMPAO and 99mTc-HMPAO at increasing concentrations and activities was tested on monolayers of the EC line EA-hy-926. The influence of temperature and time on tracer incorporation into cells was also tested. The optimal labeling conditions were applied to evaluate the retention of ECs seeded on polyester grafts under flow conditions by gamma camera detection. Results: The activity of 10 MBq/10(6) cells corresponding to 4.5 microg/10(6) cells of unlabeled HMPAO, applied for 3 h at 37 degrees C (cellular uptake = 18%), was the best compromise between the maintenance of cell viability and metabolic activity and efficient detection by the gamma camera. Spontaneous leakage was observed and analyzed by high-performance liquid chromatography. A cell loss of 13% after 180-min exposure to shear stress was obtained. CONCLUSION: Our data thus indicate the feasibility of using such a radiolabeling technique to investigate EC-biomaterial interactions.     

Quantitative analysis of 99mTc-HMPAO kinetics in epilepsy

A convection-diffusion model is applied for the determination of cerebral circulation parameters in patients with frontal lobe epilepsy. The method employs 99mTc-HMPAO, dynamic brain imaging and SPECT. The model takes into account both the capillary and cell permeabilities of HMPAO. Experiments were performed in 41 patients with epilepsy and 10 patients without evident cerebrovascular disease. The results indicate that in the inter ictal epileptic foci, cerebral blood flow was reduced (18% +/- 19%), cerebral blood volume was increased (21% +/- 14%), and the capillary permeability of HMPAO in the affected side was on the average 50% of the value in the contralateral side, whereas the reflux from brain tissue to blood was increased. These findings mean that HMPAO diffusion across the blood brain barrier is restricted and HMPAO slackly interacts with the intra cellular component of the inter ictal epileptic foci.     

99mTc-bicisate and 99mTc-HMPAO SPECT imaging in early spontaneous reperfusion of cerebral embolism.

Two patients with a cerebral embolism were evaluated by using both 99mTc-ethyl cysteinate dimer (ECD, or Bicisate) and 99mTc-hexamethylpropyleneamine oxime (HMPAO) single-photon emission computed tomography (SPECT). In one patient, 99mTc-ECD SPECT images revealed hypoactivity in a reflow hyperemic area where an infarct was seen later on CT scans. In another patient, a reperfused area showed hyperactivity on 99mTc-ECD SPECT without any abnormality on follow-up CT. 99mTc-ECD represents a potential agent with which to evaluate cerebral tissue viability in early reperfusion after ischemia.     

Usefulness of 99mTc-ciprofloxacin (infecton) scan in diagnosis of chronic orthopedic infections: comparative study with 99mTc-HMPAO leukocyte scintigraphy.

99mTc-labeled ciprofloxacin (infecton) has been developed for detecting infectious foci, which localize in high concentrations in living bacteria. Other studies performed with various infections in animals and humans have found that infecton is a promising agent with better specificity for bacterial infections than white blood cell (WBC) scans. In this study, we evaluated the efficacy of infecton scintigraphy for detecting chronic bone and joint infections. METHODS: Fifty-six sites with suspected bone or joint infection were examined with 99mTc-WBC and infecton scans in 51 patients. Of these patients, 21 had prosthetic implant materials. Biochemical, radiologic, and microbiologic data and clinical outcomes also contributed, along with the results from scintigraphic techniques, in determining the presence or absence of infection. Scintigraphic images were produced at 1 and 4 h after injection of 370-400 MBq infecton or 185-200 MBq 99mTc-hexamethylpropyleneamine oxime (HMPAO)-WBCs. For each patient, there were at least 2 d and at most 7 d between scintigraphic studies. RESULTS: There were 30 true-positive, 4 false-positive, 20 true-negative, and 2 false-negative results with infecton. With 99mTc-HMPAO-WBCs, the results were 20, 1, 23, and 12, respectively. Values for sensitivity, specificity, and accuracy were 94%, 83%, and 89%, respectively, with the infecton scan and 63%, 96%, and 77%, respectively, with WBC scanning. Differences between the two agents were statistically significant (P < 0.001). Infecton and WBC scan results were in general concordance for 43 of 56 sites (77%). Infecton results for vertebral infections were the most notable findings in this study, despite the limited number of patients with this condition. Infecton scans were positive for hot spots in five of six patients with vertebral osteomyelitis. WBC scans showed photon-deficient areas in four of these same patients and normal distribution in the remaining two patients. CONCLUSION: Infecton is a useful agent for detecting infectious foci in bones and joints. Moreover, the infecton scan seems to be a more powerful tool in diagnosing vertebral infections than WBC scintigraphy.     

Scintigraphic findings on99mTc-MDP,99mTc-sestamibi and99mTc-HMPAO images in Gaucher's disease

Gaucher's disease is an autosomal recessive lysosomal storage disease characterized by the specific deficiency of glucocerebrosidase that leads to accumulation of insoluble glucocerebroside in the reticuloendothelial system, particularly the bone marrow, liver, spleen and lymph nodes. Direct scintigraphic visualization of lipid deposits in Gaucher's disease has recently been described, based on the use of the lipid-soluble xenon-133. We report here on the use of the lipophilic cat-ionic complex technetium-99m sestamibi (^99mTc-MIBI), employed as an indicator of increased cellular density and metabolic activity, to evaluate Gaucher cell infiltrates in the bone marrow;^99mTc-hexametazime (^99mTc-HMPAO) was also employed, as a pure indicator of lipidic infiltration in the bone marrow. A 67-year-old patient with known type 1 Gaucher's disease presented with a painful left hip and knee and difficulty in gait subsequent to traumatic fracture of the left femoral neck that had required implant of a fixation screw-plaque. Bone scan with^99mTc-methylene diphosphonate revealed reduced uptake at the distal metaphyseal-epiphyseal femoral region. In addition, whole-body maps and spot-view acquisitions of the thighs and legs were recorded at both 30 min and 2.5 h after the injection of^99mTc-MIBI: the scintigraphic pattern clearly showed increased uptake at several sites involved by Gaucher deposits in the bone marrow (both knees, with variable intensity in different areas), matching the bone changes detected by conventional x-ray. The target to non-target ratios slowly decreased with time, from an average value of 2.25 in the early scan to an average value of 2 in the delayed scan. The lipid-soluble agent^99mTc-HMPAO exhibited a superimposable scintigraphic pattern of accumulation at the involved sites, though with lower target to non-target ratios (1.27–1.48). The results obtained in this patient suggest a potential role of^99mTc-MIBI in the scintigraphic evaluation of Gaucher's lipid deposits in the bone marrow. If the results are confirmed in other patients, this radiopharmaceutical would offer clear advantages over¹³³Xe because of its wider availability and greater practicality (i.v. administration of^99mTc-MIBI versus inhalation of¹³³Xe, and use of a single gamma camera instead of two as with¹³³Xe).     

Vascular dementia of Binswanger's type: clinical,neuroradiological and99mTc-HMPAO SPET study

In 24 patients with vascular dementia of Binswanger's type (VDBT) and 14 age-matched neurologically normal volunteers, we investigated the relationship between clinical features, white matter lesions (leucoaraiosis) and cerebral atrophy on computed tomography (CT) scan, and regional cerebral blood flow. All subjects underwent the Mini-Mental State Examination of Taiwan, version 1 (MMSE-T1), for assessing the severity of cognitive impairment. The patients were subdivided into two groups, one with mild to moderate (group I, MMSE-T1 scores: 11–24,n=ll), and the other with severe dementia (group II, MMSE-T1 scores: below 10,n=13). White matter degeneration was evaluated with densitometric methods. Loss of brain parenchyma was estimated with seven linear measurements (Evan's ratio, third ventricle ratio, width of temporal horn tip, anterior-posterior length of temporal horn, anterior-posterior length of Sylvian fissure and width of frontal interhemispheric fissure) by CT scans. Regional cerebral blood flow was determined with technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomography (SPET). In neuroimaging studies, subcortical leuco-araiosis was localized at the frontal region in group I patients and scattered diffusely in group II patients.^99mTc-HMPAO SPET analysis revealed reduction of regional cerebral blood flow in the frontal lobe in group I patients and widespread reduction of regional cerebral blood flow in group II patients. A correlation between frontal leuco-araiosis and perfusion defect of the frontal pole was demonstrated in group I patients, showing findings typical of subcortical dementia. There was no difference in frontal atrophic measurements between group I patients and controls. Ratios of volumes of lost brain parenchyma and leuco-araiosis were significantly higher in group II patients than in the age-matched controls, corresponding to a diffuse cerebral perfusion defect. These results suggest that patients with VDBT have early frontal lobe involvement with posterior progression. Patients with mild VDBT are more likely to show reduction of frontal cerebral blood flow and leuco-araiosis, while those with severe VDBT are more likely to have diffuse leuco-araiosis, cerebral hypoperfusion and brain atrophy.     

Quantitative analysis of99mTc-HMPAO kinetics in epilepsy

A convection-diffusion model is applied for the determination of cerebral circulation parameters in patients with frontal lobe epilepsy. The method employs^99mTc-HMPAO, dynamic brain imaging and SPECT. The model takes into account both the capillary and cell permeabilities of HMPAO. Experiments were performed in 41 patients with epilepsy and 10 patients with out evident cerebrovascular disease. The results indicate that in the inter ictal epileptic foci, cerebral blood flow was reduced (18%±19%), cerebral blood volume was increased (21%±14%), and the capillary permeability of HMPAO in the affected side was on the average 50% of the value in the contralateral side, whereas the reflux from brain tissue to blood was increased. These findings mean that HMPAO diffusion across the blood brain barrier is restricted and HMPAO slackly interacts with the intra cellular component of the inter ictal epileptic foci.     

The behavior of 99mTc-hexamethylpropyleneamineoxime (99mTc-HMPAO) in blood and brain

99mTc-hexamethylpropyleneamineoxime (99mTc-HMPAO) is a reagent for scanning cerebral blood flow. We investigated how 99mTc-HMPAO changed in the blood and brain. The 99mTc-HMPAO, which was prepared by adding of 99mTcO4- to HMPAO and Sn(II), consisted of primary and secondary complexes, reduced hydrolyzed 99mTc, and 99mTc-pertechnetate. The percentage of the primary complex in 99mTc-HMPAO decreased with time after preparation. The primary complex converted to the secondary one very rapidly in the presence of plasma. When 99mTc-HMPAO was injected into patients, 99mTc activity was immediately partitioned in the plasma fraction, with approximately 60% in whole blood. In plasma, 99mTc was found to be associated with proteins such as albumin and globulin. 99mTc trapped in red cells was not washed out with either plasma or saline. Biodistribution studies showed that the less lipophilic compounds of 99mTc-HMPAO could not pass through the blood brain barrier (BBB), and therefore did not accumulate in the brain. The results of gel chromatography and equilibrium dialysis indicated that no specific 99mTc binding protein was present in the brain. Considering the instability of 99mTc-HMPAO in vivo, we proposed that the speed at which the primary complex converted to the less lipophilic compounds was important in allowing 99mTc-HMPAO to pass through the BBB and to be fixed in the brain.     

The behavior of99mTc-hexamethylpropyleneamineoxime (99mTc-HMPAO) in blood and brain

^99mTc-hexamethylpropyleneamineoxime (^99mTc-HMPAO) is a reagent for scanning cerebral blood flow. We investigated how^99mTc-HMPAO changed in the blood and brain. The^99mTc-HMPAO, which was prepared by adding of^99mTcO _- ⁴ to HMPAO and Sn(II), consisted of primary and secondary complexes, reduced hydrolyzed^99mTc, and^99mTc0pertechnetate. The percentage of the primary complex in^99mTc-HMPAO decreased with time after preparation. The primary complex converted to the secondary one very rapidly in the presence of plasma. When^99mTc-HMPAO was injected into patients,^99mTc activity was immediately partitioned in the plasma fraction, with approximately 60% in whole blood. In plasma,^99mTc was found to be associated with proteins such as albumin and globulin.^99mTc trapped in red cells was not washed out with either plasma or saline. Biodistribution studies showed that the less lipophilic compounds of^99mTc-HMPAO could not pass through the blood brain barrier (BBB), and therefore did not accumulate in the brain. The results of gel chromatography and equilibrium dialysis indicated that no specific^99mTc binding protein was present in the brain. Considering the instability of^99mTc-HMPAO in vivo, we proposed that the speed at which the primary complex converted to the less lipophilic compounds was important in allowing^99mTc-HMPAO to pass through the BBB and to be fixed in the brain.     

99mTc-HMPAO SPECT study of cerebral perfusion after treatment with medication and electroconvulsive therapy in major depression.

Compromised regional cerebral blood flow (rCBF) in major depressive disorder may be partly reversed by successful antidepressant treatment. However, it is not known if the reversal of rCBF compromise is dependent on the mode of antidepressant treatment. The current study aimed to address this question. METHODS: Thirty-three patients (19 women and 14 men; mean age +/- SD, 53 +/- 16 y) with moderate major depressive disorder were studied before 6 wk of treatment with tricyclic antidepressants, selective serotonin reuptake inhibitors, or a course of electroconvulsive therapy, and 31 of these patients were also studied afterward. A comparison group of 25 healthy volunteers (13 women and 12 men; mean age, 49 +/- 15 y) were studied once. rCBF was assessed using 99mTc-hexamethylpropyleneamine oxime SPECT. Images were analyzed using globally normalized statistical parametric mapping localized to the Montreal Neurologic Institute brain atlas. RESULTS: Baseline rCBF was lower in depressed patients than in controls in the frontal cortex and subcortical nuclei bilaterally. A response to medication was associated with normalization of rCBF deficits, whereas a response to electroconvulsive therapy was associated with an additional rCBF decrease in the parietotemporal and cerebellar regions bilaterally. CONCLUSION: Hypoperfusion in major depressive disorder largely normalizes after a response to pharmacotherapy. Perfusion changes after a response to electroconvulsive therapy may follow a different course.     

Clinical assessment of 99mTc-HMPAO scintigraphy in thoracic tumors]

99mTc-hexamethylpropylene amineoxime (99mTc-HMPAO) scintigraphy was performed in 15 malignant tumors in 11 patients and a patient with bronchopneumonia. A high 99mTc-HMPAO affinity for the tumors was observed on SPECT, however, the mean tumor/contralateral normal lung ratios of 99mTc-HMPAO activity (1.26) was lower than that of 201Tl-chloride (2.29). 99mTc-HMPAO uptake was seen not only in the tumors but also in the bronchopneumonia, atelectasis, and irradiated lung (containing radiation fibrosis). Moreover, a diffuse uptake in the lung was seen in a patient received repeated chemotherapy. Therefore, it is emphasized that there is a non-specific 99mTc-HMPAO uptake in those various pulmonary conditions.     

Regional cerebral blood flow pattern in normal young and aged volunteers: a99mTc-HMPAO SPET study

The aim of this study was to investigate the normal pattern of regional cerebral blood flow (rCBF) distribution in normal young and aged volunteers using technetium-99m hexamethylpropylene amine oxime (^99m-Te-HMPAO) as a tracer. The region brain perfusion of young and aged subjects was compared, especially regarding rCBF differences due to age and gender, and interhemispheric rCBF asymmetries. Sixty-eight right-handed normal volunteers — 40 young (mean age 29.5±6.3 years) and 28 aged (mean age 71.2±4.3 years) — were included in the study. rCBF was estimated on the basis of a semiquantitative approach by means of a left/right index and two region/reference ratios, using the cerebellum and the whole brain activity as references. A good correlation between these two region/reference ratios was found (P<0.005 in all cerebral regions). The highest rCBF ratios corresponded to the cerebellum, followed by the occipital lobe. The remaining cortical regions (temporal, parietal, frontal and basal ganglia) showed slightly lower values. The white matter showed rCBF ratios substantially lower than the grey matter. In neither young nor aged subjects were significant rCBF differences between the genders found in any of the two region/reference indices employed. Aged subjects showed significantly lower rCBF ratios than young subjects in the left frontal lobe and in the posterior region of the left temporal lobe. In both young and aged subjects, lower perfusion was found in the left hemisphere, except for the white matter region in both age groups and the frontal lobe in the young subjects. Aged subjects presented a slightly higher interhemispheric asymmetry in the frontal lobe. However, interhemispheric asymmetry was minimal (–1.01% to 3.14%). Consequently, a symmetrical rCBF distribution can be assumed between homologous regions, independent of age.