Identification of factors affecting technetium 99m leucocyte labelling by phagocytic engulfment and evelopment of an optimal technique

Human autologous leucocytes can be simply and reproducibly labelled by phagocytic engulfment of technetium 99m stannous colloid with high leucocyte-labelling efficiency (LLE), similar human biodistribution to indium-111-oxine labelled leucocytes and good cell viability. A mean particle size of 2.1 ms is optimal for phagocytosis and the most important parameter in maintaining reproducibly high neutrophil uptake. It is more critical than hitherto appreciated. When such variables as type of colloid, purity of starting materials, speed of mixer rotation when preparing colloid and labelling leucocytes, heparin concentration, freshness of colloid preparation, type of sterilising membrane filter used and incubation time of cells with colloid are rigidly controlled, consistent labelling efficiencies in excess of 90% can be obtained with neutrophil predominance. The lyophilised kit tested produced suboptimal results.     

Uptake of technetium 99m MDP by hepatoblastoma

Focal uptake of 99mTc-MDP was seen in a case of hepatoblastoma. The focal uptake corresponded to an area of calcification on CT, which was shown histologically to consist of osteoid with mineralization. The mechanism of uptake by the tumor in this case is likely to be the same as for skeletal uptake.     

Uptake of technetium 99m MDP by hepatoblastoma

Focal uptake of ^99mTc-MDP was seen in a case of hepatoblastoma. The focal uptake corresponded to an area of calcification on CT, which was shown histologically to consist of osteoid with mineralization. The mechanism of uptake by the tumor in this case is likely to be the same as for skeletal uptake.     

Comparison of imaging properties of technetium 99m Q12 and technetium 99m Q3 in humans

Background

This study was a direct comparison of the imaging characteristics of ^99mTc-labeled Q12 (^99mTc-Q12) and ^99mTc-labeled Q3 (^99mTc-Q3) in the same patients.

Methods and Results

In 10 patients with known angiographic coronary artery anatomy, ^99mTc-Q12 and ^99mTc-Q3 myocardial imaging were performed. Tomographic myocardial imaging was started 15 minutes after tracer injection at rest and with treadmill exercise. Ratios of heart-to-lung and heart-to-liver activity were calculated from the anterior plane projections of the tomograms at 20 minutes after tracer injection. The presence or absence of angiographic coronary artery disease was correctly determined from ^99mTc-Q12 images in 10 of 10 patients with ^99mTc-Q12 and in 9 of 10 patients with ^99mTc-Q3. The presence or absence of a greater than 50% stenosis in an individual coronary vessel was correctly predicted for 26 of 30 vessels with ^99mTc-Q12 (87%) and in 27 of 30 vessels with ^99mTc-Q3 (90%, p=NS vs ^99mTc-Q12). Mean heart-to-lung activity ratio at rest was 1.50 for ^99mTc-Q12 and 1.93 for ^99mTc-Q3 (p<0.01). Mean heart-to-liver activity ratio at rest for ^99mTc-Q12 was 0.78 versus 0.54 for ^99mTc-Q3 (p<0.0001).

Conclusions

In 10 patients with chest pain and angiographically defined coronary anatomy, ^99mTc-Q12 and ^99mTc-Q3 provided similar detection of coronary artery stenoses. At 20 minutes after tracer injection, heart-to-liver activity ratios were more favorable for ^99mTc-Q12 than for ^99mTc-Q3, but ^99mTc-Q3 resulted in a more favorable ratio of heart-to-lung activity.     

Assessment of inflammatory bowel disease by using two different (99m)Tc leucocyte labelling methods

The aim of this study was to retrospectively compare the diagnostic accuracy of (99m)Tc hexamethylpropyleneamine oxime (HMPAO) white blood cell scintigraphy in patients with a suspicion of active inflammatory bowel disease by using two different cell suspension media: leukocyte poor plasma (LPP) and Hanks' balanced salt solution (HBSS). Leukocytes from 30 patients were labelled using LPP and in 28 cases using HBSS. In the LPP method the leukocytes were resuspended in 0.5 ml cell-free plasma while in the HBSS method the cells were resuspended in 0.5 ml HBSS. Scintigraphic images were obtained at 30 min and 2 h after injection of 185-200 MBq (99m)Tc-HMPAO leukocytes. The leukocyte labelling efficiency was 65.5% and 89.0%, respectively, for the LPP and HBSS methods. There were 22 true positive, seven true negative and one false negative result in the LPP group, while in the HBSS group results were 18, nine and one, respectively. Diagnostic accuracy was similar with both methods although sensitivity was slightly higher in the HBSS group. In summary, these date indicate that leukocyte scintigraphy labelling using HBSS as the resuspension medium should be used as a first option for white blood cell labelling and diagnosis of inflammatory bowel disease.     

Comparison of technetium 99m polyclonal human immunoglobulin and technetium 99m monoclonal antibodies for imaging chronic osteomyelitis

The accuracy of technetium-99m human immunoglobulin (HIG) for the detection of chronic osteomyelitis (OM) was compared with white blood cell scintigraphy using^99mTc-labelled monoclonal mouse antibodies (MAB). Seventeen patients suspected of having OM in 20 lesions went through three-phase skeletal scintigraphy, HIG scintigraphy and MAB scintigraphy. The final diagnosis was established by open surgery, histology and bacteriology. Chronic OM was proved in 14/20 lesions. Six of these 14 infections were located in peripheral areas without active bone marrow and 8/14 in central areas with active bone marrow. In peripheral OM, 5/6 with HIG and 6/6 with MAB were true positives. In the central skeleton all 8/8 infections appeared as cold lesions in the MAB study, which were defined as being false negative due to their non-specificity. Using HIG, 5/8 central infections were determined to be truly positive by showing photon-rich lesions. These 5 lesions were located in the hip region and in the pelvis, whereas 3 lesions of the spine were missed. There were no false-positive results in either studies. In conclusion, MAB was superior to HIG in peripheral OM concerning sensitivity, anatomical landmarks and differentiation of soft tissue versus bone infection. In central OM MAB detected all lesions accurately, but no differential diagnosis was possible due to the non-specificity of photon-low areas. In this respect HIG seems to be more specific due to the increased accumulation even in central infection sites.     

Comparison of technetium 99m polyclonal human immunoglobulin and technetium 99m monoclonal antibodies for imaging chronic osteomyelitis. First clinical results

The accuracy of technetium-99m human immunoglobulin (HIG) for the detection of chronic osteomyelitis (OM) was compared with white blood cell scintigraphy using 99mTc-labelled monoclonal mouse antibodies (MAB). Seventeen patients suspected of having OM in 20 lesions went through three-phase skeletal scintigraphy, HIG scintigraphy and MAB scintigraphy. The final diagnosis was established by open surgery, histology and bacteriology. Chronic OM was proved in 14/20 lesions. Six of these 14 infections were located in peripheral areas without active bone marrow and 8/14 in central areas with active bone marrow. In peripheral OM, 5/6 with HIG and 6/6 with MAB were true positives. In the central skeleton all 8/8 infections appeared as cold lesions in the MAB study, which were defined as being false negative due to their non-specificity. Using HIG, 5/8 central infections were determined to be truly positive by showing photon-rich lesions. These 5 lesions were located in the hip region and in the pelvis, whereas 3 lesions of the spine were missed. There were no false-positive results in either studies. In conclusion, MAB was superior to HIG in peripheral OM concerning sensitivity, anatomical landmarks and differentiation of soft tissue versus bone infection. In central OM MAB detected all lesions accurately, but no differential diagnosis was possible due to the non-specificity of photon-low areas. In this respect HIG seems to be more specific due to the increased accumulation even in central infection sites.     

Differentiation of myocardial ischemia and necrosis by technetium 99m glucaric acid kinetics

Background  Current clinical approaches may not always be helpful in the early differentiation of necrotic tissue from ischemic viable myocardium in patients with acute myocardial infarction. Tc-99m-glucaric acid is a carbohydrate ligand that may permit differentiation of necrosis from ischemia. However, the myocardial kinetics of Tc-99m-glucaric acid have not been well defined early after myocardial injury. The aim of this study was to evaluate the effect of necrosis in comparison to postischemic injury alone on the kinetics of Tc-99m-glucaric acid with the use of an isolated perfused rat heart model. Methods and Results  Three groups of hearts were studied: group I: control (n=6); group II: postischemia (15 minutes of no flow with complete reperfusion, n=6); and group III: necrosis (90 minutes of no flow to induce necrosis with complete reperfusion, n=6). Tc-99m-glucaric acid (1.3±0.6 mCi/L of buffer) was perfused for 30 minutes to evaluate tracer accumulation. Then tracer-free buffer was perfused for 45 minutes to evaluate clearance. The peak accumulation relative to the control group mean was significantly increased (p<0.01) in group III (necrosis) 254%±75%) compared with control (100%±10%) and compared with postischemia (108%±26%). On kinetic data analysis, the monoexponential clearance rate constant (k_c) was significantly reduced with necrosis (control: k_c=20.2±14.0×10⁻⁴ sec⁻¹; postischemia: k_c=22.3±15.2×10⁻⁴ sec⁻¹; and necrosis: k_c=1.2±0.3×10⁻⁴ sec⁻¹;p<0.05). A retention fraction was calculated from the activity after 45 minutes of clearance corrected for the peak activity for each group. The necrotic group had significant myocardial retention in comparison to control and postischemia (control: 12%±8%; postischemia: 14% ±16%; necrosis: 64%±10%;p<0.01). Conclusions  The accumulation and retention of Tc-99m-glucaric acid is markedly increased in the presence of myocardial necrosis in comparison to control and postischemic myocardial injury. In this model, Tc-99m-glucaric acid is capable of defining the presence of necrotic myocardial injury in comparison to postischemic injury alone., This agent may have potential application for the early differentiation of ischemic from necrotic myocardium in acute myocardial infarction. Supported in part by a grant from the JP Bickell Foundation of Ontario, Canada. Dr. Beanlands is a Research Scholar for the Medical Research Council of Canada. Dr. Ruddy is a Research Scholar for the Heart and Stroke Foundation of Canada. Presented in part at the 67th Scientific Sessions of the American Heart Association Meeting, 1994. Submitted for publication April 4, 1996; revision accepted Nov 27, 1996.     

Images of liposarcoma using technetium-99m bleomycin and technetium (V)-99m DMSA

The effectiveness of Tc-99m bleomycin (BLM) and Tc(V)-99m DMSA are compared with that of Ga-67 citrate, which is currently the most widely used agent. In four patients with lipomatous tumors, the clinical significance of tumor imaging with each of these three agents is discussed and compared. Results indicate that both Tc-99m BLM and Tc(V)-99m DMSA are superior in detecting the extension or localization of liposarcomas.     

Preclinical evaluation of technetium 99m-labeled P1827DS for infection imaging and comparison with technetium 99m IL-8

BACKGROUND: The technetium 99 m (99mTc)-radiolabeled, leukocyte-avid peptide-glycoseaminoglycan complex, [99mTc]P1827DS, has been synthesized as an improved infection/inflammation imaging agent to [99mTc]P483H (LeukoTect, Diatide). In a phase I/II clinical trail, [99mTc]P483H images were equivalent to those obtained with 111In ex vivo labeled leukocytes. However, there was physiologic accumulation of radioactivity in the body that could hamper interpretation of the images. In this study, the potential of [99mTc]P1827DS for infection imaging was assessed in comparison with [99mTc]P483H and the well-described imaging agent [99mTc] hydrazinonicotinamide (HYNIC)-interleukin 8 (IL-8). METHODS: The binding of [99mTc]P1827DS to human blood cell was studied in vitro. A rabbit Escherichia coli infection model was used to perform the biodistribution and imaging studies with [99mTc]P1827DS, [99mTc]P483H and [99mTc]HYNIC-IL-8. RESULTS: [99mTc]P1827DS binds to leukocytes but not to erythrocytes. The leukocyte binding was not saturable up to an investigated concentration of 10 microM. The accumulation of [99mTc]P1827/DS at the infection site strongly depends on the P1827/DS ratio and was optimal at a molar ratio of 10:1. [99mTc]P1827DS shows improved biodistribution over [99mTc]P483H with similar uptake at the infection site. Abscess uptake of [99mTc]HYNIC-IL-8 was approximately three times higher than that of [99mTc]P1827DS. [99mTc]HYNIC-IL-8 showed high accumulation in the kidneys, whereas [99mTc]P1827DS showed high lung uptake and slightly higher accumulation in the liver and spleen. CONCLUSION: [99mTc]P1827DS is a potential new inflammation imaging agent, which clearly visualized the abscess in the rabbit E. coli infection model and showed improved biodistribution compared to [99mTc]P483H. However, the infection uptake and biodistribution of [99mTc]P1827DS is not superior to that of [99mTc]HYNIC-IL-8 in this animal model.     

Analysis of factors affecting uptake of Tc-99m Sn-N-pyridoxyl-5-methyltryptophan by hepatocellular carcinoma

We performed Tc-99m PMT imaging in 176 patients with HCC and evaluated factors affecting^99mTc-PMT uptake by HCC with a logistic model. The probability of HCC showing increase in uptake of the radioisotope was 104.6 times higher in patients with the Ed I type than in those with the Ed III type and 12.1 times higher in patients with a tumor diameter of 5.0–7.9 cm than in those with a tumor diameter of 2.0–5.0 cm. Among the other variables, the serum AFP level and sex were suggested to have effects similar to those of the tumor size on Tc-99m PMT uptake by HCC. The grade of morphological differentiation of the tumor was therefore most markedly related to Tc-99m PMT uptake.     

Relative uptake of technetium 99m stannous colloid by neutrophils and monocytes is altered by gram-negative infection

Gram-negative infection alters phagocytic cell function; hence, it could affect phagocytic uptake of inorganic colloids by these cells. Neutrophil and monocyte uptake of technetium 99m stannous colloid (99mTc SnC) in whole blood was measured in 10 patients with gram-negative infection (Burkholderia pseudomallei) and 7 controls. Mean uptake per individual neutrophil was reduced in infection. Uptake per monocyte was not significantly different. Blood from six normal individuals was incubated with lysed B. pseudomallei and colloid, which showed reduced neutrophil uptake, but increased monocyte uptake. These results indicate that uptake of 99mTc SnC stannous colloid can be used to measure alteration in phagocytic cell function. They suggest that infection with B. pseudomallei is associated with reduced phagocytosis by individual neutrophils, possibly through toxic effects of bacterial products. This could have immunopathogenic consequences for this gram-negative infection and may explain why it responds to granulocyte colony-stimulating factor.     

Estimation of technetium 99m mercaptoacetyltriglycine lasma clearance by use of one single plasma sample

Recent studies have shown that technetium 99m mercaptoacetyltriglycine (MAG-3) is a suitable replacement for iodine 131 or 123 hippurate in gammacamera renography. Also, the determination of its clearance is of value, since it correlates well with that of hippurate and thus may be an indirect measure of renal plasma flow. In order to simplify the clearance method we developed formulas for the estimation of plasma clearance of MAG-3 based on a single plasma sample and compared them with the multiple sample method based on 7 plasma samples. The correlation to effective renal plasma flow (ERPF) (according to Tauxe's method, using iodine 123 hippurate), which ranged from 75 to 654 ml/min per 1.73 m², was determined in these patients. Using the developed regression equations the error of estimate for the simplified clearance method was acceptably low (18–14 ml/min), when the single plasma sample was taken 44–64 min post-injection. Formulas for different sampling times at 44, 48, 52, 56, 60 and 64 min are given, and we recommend 60 min as optimal, with an error of estimate of 15.5 ml/min. The correlation between the MAG-3 clearances and ERPF was high (r = 0.90). Since normal values for MAG-3 clearance are not yet available, transformation to estimated ERPF values by the regression equation (ERPF=1.86 × C_MAG-3 + 4.6) could be of clinical value in order to compare it with the normal values for ERPF given in the literature. Offprint requests to: R. Müller-Suur     

Technetium-99m labelling of the anti-tumour antibody PR1A3 by photoactivation

Irradiation of antibody with ultraviolet light leads to reduction of disulphide bonds. Thus irradiation can be used to generate free thiols prior to direct labelling of antibody with technetium-99m, and has a potential advantage over methods using chemical reducing agents such as mercaptoethanol or tin, in that no purification step is needed to remove excess reducing agent. We have used the photoactivation method developed by Sykes et al. to label the anti-tumour antibody PR1A3 with^99mTc. The antibody was irradiated at 300 nm using a Rayonet photochemical reactor with eight RMR3000 lamps. In a typical experiment, the antibody solution was injected into a nitrogen-filled borosilicate glass vial and purged with nitrogen. A degassed solution containing stannous fluoride and methylene diphosphonate was then added to the antibody and the vial was irradiated. Following the irradiation, [^99mTc]pertechnetate was injected into the vial and the reaction mixture was incubated for 30 min at room temperature before being analysed by size-exclusion high-pressure liquid chromatography and instant thin-layer chromatography. Labelling yields greater than 95% were obtained using antibody concentrations ranging from 0.5 mg/ml to 5 mg/ml. Irradiation times as short as 5 min and tin to antibody ratios in the range between 11 and 32 µg tin per mg antibody gave high labelling yields. Labelling yields greater than 95% were obtained after storage of the photoactivated antibody at –70° C for several weeks. The stability of the^99mTc-labelled photoactivated PR1A3 was similar to that of^99mTc-labelled mercaptoethanol-reduced PR1A3. The mean immunoreactive fraction was 77% for the photoactivation-labelled PR1A3, compared to 93% for PR1A3 labelled by mercaptoethanol reduction. Biodistribution studies were carried out using^99mTc-photoactivation-labelled PR1A3 or PR1A3 labelled by mercaptoethanol reduction in Balb/c mice and in nude mice with MKN-45 human tumour xenografts. There was no significant difference in tumour uptake between the mice that received photoactivated PR1A3 and those that received mercaptoethanol-reduced PR1A3. There was also no significant difference in uptake in most organs in Balb/c mice; however, the photoactivated antibody cleared more rapidly from the blood, and whole-body clearance was also faster for the photoactivated PR1A3. In conclusion, the photoactivation technique provides a very convenient one-pot method for labelling antibodies with^99mTc.