99mTc-human Serum Albumin Research Articles

Enhanced tumor imaging with pokeweed mitogen

Traditional tumor imaging with biotracer techniques relies solely on the target specificity of the biomolecule. We hypothesize that specific imaging is possible by altering the rate of tissue clearance (both normal and aberrant) of any given radiotracer. Pokeweed mitogen (PWM) as a biomodulator, represents a class of molecules which regulate cellular differentiation and cell-cell interactions and, as part of these mechanisms alter tissue clearance rates (both normal and aberrant). Utilizing the B-16/C57BL/6 model, 7 days post-transplantation (which represents log phase growth of the tumor), 10 animals were imaged following an i.v. injection of 1–2 mCi 99mTc-PWM in order to visualize the tumors and determine the optimal imaging kinetics. A specific tumor image is achieved between 120 and 240 min post-injection. In addition, tumor imaging studies using a non-tumor-specific biomolecule were conducted by injecting 19 animals i.v. with 1–2 mCi of 99mTc-human serum albumin (HSA). Twelve of these animals were given 10 μg of PWM i.p. at various intervals prior to the 99mTc-HAS administration. Imaging and biodistribution studies were performed at various intervals up to 2 h post- 99mTc-HSA injection. A 32-59% increase in the tumor-to-muscle ratio was observed in the PWM-treated animals relative to the non-treated controls. To further investigate the PWM-induced tissue clearance alteration hypothesis, tissue clearance studies using 99mTc-diethylenetriaminepentaacetic acid (DTPA) were conducted in non-tumor bearing ICR mice and the B-16/C57BL/6 tumor bearing animals. 99mTc-DTPA normal tissue clearance rates were significantly increased in the PWM treated animals relative to the non-treated controls. The use of PWM, and perhaps other structurally defined biomodulators may afford the opportunity to image aberrant tissue without the need for specialized tumor-specific preparations or may enhance the intrinsic properties of biologically-specific agents.

Clearance of 99mTc-labeled albumin from lungs in anesthetized guinea pigs.

Gamma imaging was used to measure the rate of clearance of aerosolized 99mTc-human serum albumin (HSA) from the lungs of control guinea pigs and guinea pigs that received increased lung inflation or lung injury. Anesthetized guinea pigs were ventilated for 6 min with an aerosol of HSA and the radioactivity in the chest was monitored for 2 h with a gamma camera to determine whether the clearance rate would be a reliable assessment of lung epithelial permeability. Increased lung volumes were effected by application of 5 or 7 cm H2O positive end-expired pressure (5-PEEP and 7-PEEP, respectively). Lung injury was induced either by intravenous oleic acid (OA, 27-73 microliters/kg) or inhalation of nitrogen dioxide (NO2, 80-100 ppm) for 2 h. Postmortem extravascular lung water volume (EVLW) provided an assessment of the degree of lung injury. Tracer clearance rates in animals receiving 5 or 7 cm H2O PEEP were not significantly different from controls (K = 0.15 +/- 0.05 and 0.24 +/- 0.10 vs 0.12 +/- 0.03%/min, respectively, p > .05). Animals exposed to NO2 had faster tracer clearance rates (K = 0.33 +/- 0.21%/min, p < .05) and higher EVLW (5.8 +/- 3.0 vs 3.7 +/- 0.2 mL/g dry lung, p < .05) than controls. Clearance rates of HSA from the lungs of NO2-exposed guinea pigs correlated well with injury as assessed by EVLW (r = .93, p < .01). Clearance rates of HSA and EVLW in animals receiving oleic acid were significantly higher than controls and the group receiving 5 cm H2O PEEP (K = 0.58 +/- 0.41%/min, EVLW = 8.1 +/- 0.8 mL/g dry lung tissue, p < .05), but there was no correlation between these parameters in this injury model. It is concluded that imaging of the disappearance of radiolabeled HSA in the guinea pig can be a useful index of lung epithelial permeability, but this technique is limited to certain models of lung injury.

Bone marrow (reticuloendothelial system) scintigraphy for haematological follow-up of radiochemotherapy-treated patients.

To assess the bone marrow capacity before a new treatment decision, 99mTc-human serum albumin bone marrow scintigraphy (with qualitative and quantitative evaluation) was performed in 32 patients with solid tumours or malignant lymphomas previously treated with radiochemotherapy. In the group with a normal bone marrow capacity, the blood counts were normal (14/16 cases) or became normal (2/16 cases) in the follow-up period, and the examined marrow samples exhibited normal haemopoiesis. In the group with a reduced bone marrow capacity, one or more blood counts were low in 14/16 cases. Decreased haemopoiesis was observed in only 4 of 8 examined marrow samples. The following conclusions were drawn. (1) A scintigraphically normal bone marrow capacity relates to normal haematological parameters, and therefore treatment plans could be decided on. (2) Although a reduced bone marrow capacity indicates pathological haematological conditions in the majority of cases, further studies are needed to evaluate its precise significance. (3) Application of this non-invasive, inexpensive, repeatable, non-immunizing method is recommended before a therapeutic plan is decided on for patients at considerable haematological risk.

Delivery of a nebulized aerosol to a lung model during mechanical ventilation. Effect of ventilator settings and nebulizer type, position, and volume of fill.

Several factors may affect the delivery of a nebulized aerosol to the lung through an endotracheal tube during mechanical ventilation. To study these factors in vitro, a model representing ventilation of an adult patient was constructed by linking a Servo 900C ventilator to a standard humidified circuit and an endotracheal (ET) tube positioned within a pipe representing the trachea. This was connected via a filter to a lung simulator. Nebulizers filled with 99mTc human serum albumin were positioned in the circuit, and the delivery of nebulized aerosol through the ET tube into the filter was measured using a gamma camera. With the use of an inspiratory phase-activated System 22 Acorn jet nebulizer, typical adult ventilator settings, and a 3-ml nebulizer solution volume, 5.4% of the nebulizer dose reached beyond the end of the ET tube. This was increased by increasing the inspiratory time, reducing the respiratory rate or respiratory minute volume, and by repositioning the nebulizer on the inspiratory limb of the Y-piece and was reduced by slowing the driving gas flow to the nebulizer. Under the same conditions, delivery was 3.1 and 4.4% using the Samsonic and Fisoneb ultrasonic nebulizers, respectively. Increasing the fill volume and the addition of an aerosol storage chamber increased delivery with all three nebulizers. These experiments suggest some simple ways of improving aerosol delivery during mechanical ventilation, including increasing the volume of nebulizer fill, repositioning the nebulizer in the ventilator circuit, adding an aerosol storage chamber, and adjusting ventilator settings to maximize delivery.

Liver blood flow: non-invasive estimation using a gamma camera.

A non-invasive radioisotope technique for the measurement of total liver blood flow (TBF) is described. The method requires the use of two intravenously administered tracers, 99mTc (technetium 99m) human serum albumin (HSA) and 99mTc colloid. Computer analysis of first-pass time activity curves for HSA for liver and lung tissues yields values for the arterial and portal contributions to liver blood flow, from which TBF can be determined. These values are then corrected for attenuation using the images of the colloid distribution. The use of the method is illustrated in 17 subjects. Assumptions, limitations and possible applications of the technique are discussed.

An analysis of a radionuclide technique used to measure reactive hyperaemia in limbs

A radionuclide technique (PT) for measuring the blood flow to a limb during reactive hyperaemia is described and analysed. Patients are positioned with lower limbs within the field of view of the gamma camera and pneumatic cuffs are placed below the knees to isolate the blood and induce a hyperaemic response. The remaining blood pool is labelled with 99Tc m-human serum albumin. Following release of the occlusion the rate of inflow to the limb of the radionuclide is measured and hyperaemic flow then determined, during the initial phase of the hyperaemia. The results may be analysed using a single compartment to represent the vascular pool in the lower limb. During the initial phase, activity entered the pool at a constant rate from which the blood flow may be calculated. Results were obtained in a group of 20 normal control volunteers and 20 patients with occlusive arterial disease. They indicate that following release of the cuff the blood flow rises rapidly (within 1–2 s) to a constant value which is maintained for at least 10–12 s in normal subjects and a longer period in arteriopaths. The mean flow in the normal group was 14.4 ml 100 ml min −1 and in the arteriopathic group was 4.6 ml 100 ml min −1 . The constant flow measured by PT during the initial phase of reactive hyperaemia appears to differ from the results of venous occlusion plethysmography and washout of a freely diffusible traces and possible reasons for these differences are discussed.

Quantitative lymphoscintigraphy using 99Tcm human serum albumin in patients with previously treated uterine cancer

To evaluate the clinical usefulness of lymphoscintigraphy using 99Tcm human serum albumin (99Tc-HSA) in assessing lymphoedema in the lower extremities, lymphoscintigraphy was performed by subcutaneous injection of 7.4 MBq of 99Tcm-HSA in 26 patients with uterine cancer, previously treated by operation (OP) and/or radiation therapy (RT), and in five controls. Radioactivity at the injection site in the lower extremities was counted for 3 min at 10 min (A) and at 3 h (B) after injection, and clearance of 99Tcm-HSA was defined as (1-(B)/(A)) x 100(%). Clearance in controls was 46.8 +/- 3.9%, which was significantly more than those in the other treatment groups. Clearances in patients treated with both OP and RT were less than those in patients treated with either OP or RT alone (30.1 +/- 11.4 vs. 41.9 +/- 8.9, 43.7 +/- 9.6%, respectively; p less than 0.01). The clearance in legs with lymphoedema was less than those without lymphoedema in patients treated with both OP and RT (16.6 +/- 7.7 vs. 34.9 +/- 9.3%; p less than 0.01) and in patients treated with RT (33.1 +/- 7.4 vs. 48.0 +/- 5.6%; p less than 0.01). There was a significant difference between clearance in controls and clearance in non-oedematous patients' legs treated with OP and RT (p less than 0.01). In patients treated with RT alone, radiation dose was closely correlated with 99Tcm-HSA clearance and with the development of lymphoedema. These data suggest that lymphoscintigraphy using 99Tcm-HSA is useful in evaluating lymphoedema and that radiation dose is one of the factors in the development of lymphoedema.

Lymphoscintigraphic assessment of leg oedema following arterial reconstruction using a load produced by standing

Lymphoscintigraphy using a test involving standing from a supine position and performed following an intradermal injection of 99Tcm-human serum albumin (HSA) was developed to evaluate the function of the lymphatic system in the lower extremities of patients who developed lymphoedema following arterial reconstructive surgery. In normal subjects, the load produced by standing tended to increase lymphatic function as indicated by the frequent appearance of a large spiking wave and a rapid stepwise increase in tracer activity and, less often, a phase of decreasing tracer activity. However, there was either no or less activation of lymph flow following standing in the group which developed leg oedema postoperatively. These findings indicate that lymphatic disruption is responsible for the leg oedema seen in these patients. Performance of this test following an intradermal injection of 99Tcm-HSA is technically simple, requires no special apparatus, and can be completed in 30 min. Lymphoscintigraphy using our new method can provide useful information on abnormalities in lymphatic function.

Massive Intestinal Albumin Loss after Fontan Operation

Massive intestinal protein loss was demonstrated and the site of loss determined by abdominal scintigraphy with 99mTc-labeled human serum albumin in a 9-year-old girl following the Fontan operation for pulmonary atresia with intact ventricular septum. Significant activity accumulating in the lower small intestine and moving with its contents into the colon were shown. Her condition may have resulted from intestinal lymphangiectasia, caused by increased central venous pressure. Abdominal scintigraphy with 99mTc-human serum albumin is useful in the diagnosis of protein-losing enteropathy.

Which apparatus for inhaled pentamidine? A comparison of pulmonary deposition via eight nebulisers

Aerosolised pentamidine 300 mg in 5 or 6 ml solution was administered via 8 different nebuliser systems to 12 patients with acquired immunodeficiency syndrome. Using 99mTc human serum albumin as an indirect marker for pentamidine, pulmonary, extrapulmonary (gastric and oropharyngeal) and alveolar deposition of pentamidine were measured using a gamma camera. Side effects (visual analogue scales) and changes in lung function associated with each treatment were also quantified. Deposition was completed more rapidly with the ultrasonic than the jet nebulisers. Mean total pulmonary depositions (mg +/- SEM) were Respirgard II, 6.1 +/- 0.5; Centimist, 7.3 +/- 1.0, System 22 Mizer, 14.3 +/- 2.1; System 22 Mizer with particle separator; 4.5 +/- 0.4; System 22 Mizer with Optimist 2, 6.3 +/- 0.9; Fisoneb, 6.0 +/- 1.2; Pentasonic (Portasonic); 4.6 +/- 0.9; Samsonic, 2.9 +/- 0.4. Differences between the nebulisers for peripheral lung and alveolar deposition reflected this pattern. Side effects scores were largest with System 22 Mizer, Pentasonic (Portasonic), and Fisoneb, and these produced the greatest oropharyngeal and gastric deposition. The largest reductions in lung function were associated with System 22 Mizer. A 300 mg dose of pentamidine nebulised via Respirgard II is known to be effective prophylaxis for Pneumocystis carinii pneumonia when given once monthly. Our results show that equivalent pulmonary deposition can be produced by other nebulisers. System 22 Mizer gives over twice the deposition associated with Respirgard II, and used with a pentamidine dose of 150 mg is likely to produce an adequate lung dose for prophylaxis. This nebuliser, however, is associated with more marked side effects.

Tc-99m Human Serum Albumin Lymphoscintigraphy in Lymphedema of the Lower Extremities

Edema of the lower extremities is a difficult clinical problem. It can be due to stasis, obstruction of the lymphatic channels, increased production of lymph beyond the drainage capacity of the lymphatic vessels. It is often difficult to differentiate between these varieties. Lymphoscintigraphy was performed on 164 patients complaining of swelling of the lower extremities and on 5 volunteers. All patients were injected with 1 mCi of Tc-99m human serum albumin (HSA) intradermally in the medial web of the dorsum of each foot. Data were acquired dynamically for both inguinal regions for 45 minutes, and static images of the legs, thighs, and pelvis were taken at 90 minutes. Time activity curves were generated for the equal regions of inguinal nodes on both inguinal sides. The following patterns were recognized: normal (5 volunteers and 57 patients), enhanced (17 patients), stasis with mild obstruction (70 patients), and marked stasis with obstruction (20 patients).

Measurement of microvascular permeability to small solutes in man: limitations of the technique

The aim was to evaluate the limitation on the measurement of the clearance rate of a small solute, 99mTc DTPA, from intravascular to extravascular spaces imposed by diffusion of the solute back into blood during the period of measurement. The technique for measuring clearance also generates the regional plasma volume from which the solute is cleared. Back diffusion would result in an overestimation of this plasma volume. By applying the same technique to 99mTc labelled human serum albumin, which is not cleared over the period of measurement, a separate estimate of plasma volume can be made. The subjects were eight patients undergoing routine 99mTc DTPA renography for suspected outflow obstruction. The ratio of plasma volumes based respectively on 99mTc DTPA and human serum albumin in a region of interest below the kidney was 1.04 (SD 0.09). The technique requires a region of interest over the cardiac blood pool from which the blood level of 99mTc DTPA is continuously monitored. When a correction was made for extravascular 99mTc DTPA in this cardiac region of interest, the ratio was unchanged: 0.97 (0.12). The technique is capable of measuring the clearance of 99mTc DTPA although, because of its small molecular size, the transfer rate is blood flow dependent, ie, its PS product is greater than its clearance.

Studies of the Labelling of Human Serum Albumin with 99mTc Using Sn(II) Tartrate and Sn(II)Cl2 as Reducing Agents

A comparative study has been carried out on the effect of Sn(II) tartrate and Sn(II)Cl2 on the labelling efficiency and tissue distribution of 99mTc-human serum albumin. The effect of reductant content, reaction time (incubation time), albumin content, pH, and ascorbic acid on the efficiency of labelling and the tissue distribution of the labelled albumin has been investigated. The percent labelling was determined by paper and thin layer radiochromatography. Ascorbic acid shows no effect on either labelling efficiency or tissue distribution of 99mTc-HSA prepared by Sn(II) tartrate or Sn(II)Cl2.

Cerebral blood flow and cerebral hematocrit in patients with cerebral ischemia measured by single-photon emission computed tomography.

Single-photon emission computed tomography (SPECT) was used for the measurement of regional cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral hematocrit (Hct). CBF was measured using N-isopropyl-p-I-123-Iodoamphetamine. CBV was measured by both RBC tracer (Tc-99m RBC) and plasma tracer (Tc-99m human serum albumin) and cerebral hematocrit (Hct) was calculated. In normals, the cerebral-to-large vessel Hct ratio was 75.9%. Isovolemic hemodilution in patients with high Hct tended to increase the cerebral-to-large vessel Hct ratio. Low CBF, high CBV and slow cerebral blood mean transit time (MTT by dynamic CT scanning) was seen during the acute stage of completed infarction and during the symptom-free interval of TIA. Cerebral Hct was increased in the ischemic region of poor prognosis.

Comparison of three tracers for detecting lung epithelial injury in anesthetized sheep

We compared the ability of three aerosolized tracers to discriminate among control, lung inflation with a positive end expired pressure of 10 cmH2O, lung vascular hypertension and edema without lung injury, and lung edema with lung injury due to intravenous oleic acid. The tracers were 99mTc-diethylenetriaminepentaacetate (99mTc-DTPA, mol wt 492), 99mTc-human serum albumin (99mTc-ALB, mol wt 69,000), and 99mTc-aggregated albumin (99mTc-AGG ALB, mol wt 383,000). 99mTc-DTPA clearance measurements were not able to discriminate lung injury from lung inflation. The 99mTc-AGG ALB clearance rate was unchanged by lung inflation and increased slightly with lung injury. The 99mTc-ALB clearance rate (0.06 +/- 0.02%/min) was unchanged by lung inflation (0.09 +/- 0.02%/min, P greater than 0.05) or 4 h of hypertension without injury (0.09 +/- 0.04%/min, P greater than 0.05). Deposition of 99mTc-ALB within 15 min of the administration of the oleic acid increased the clearance rate to 0.19 +/- 0.06%/min, which correlated well with the postmortem lung water volume (r = 0.92, P less than 0.01). This did not occur when there was a 60-min delay in the deposition of 99mTc-ALB. We conclude that 99mTc-ALB is the best indicator for studying the effects of lung epithelial injury on protein and fluid transport into and out of the air spaces of the lungs in a minimally invasive manner.

Diagnosis of thrombosis of the deep veins of the lower extremities and pelvis and pulmonary thromboembolism using 99Tcm human serum albumin macroaggregates.

Radionuclide phlebography of the lower extremities, pelvis and pulmonary scintigraphy was performed using 99Tcm human serum albumin macroaggregates (MAA) in 90 patients aged 20 to 80 years, 13 (14%) in post-operative period and 77 (85%) with suspected deep venous thrombosis or pulmonary thromboembolism. The aim of the study was to evaluate the diagnosis of thrombosis of the deep veins of the lower extremities and pelvis and pulmonary thromboembolism using a refined technique. Deep venous thrombosis (DVT) was detected in all surgical patients and in 59 patients with systemic diseases. Perfusion scintigraphic defects characteristic of pulmonary thromboembolism (PE) were discovered in 12 of the surgical patients and in 38 of the medical patients. The results of the examinations have again shown that patients after surgery are exposed to high risks of DVT and pulmonary thromboembolism, while a relatively high percentage of normal findings in patients with suspected DVT have indicated unreliability of clinical symptoms and signs in diagnosing this disease.

Gastric emptying in marathon runners.

Radionuclide gastric emptying studies using 99m-Tc human serum albumin egg omelette have been carried out in 10 long distance runners at rest and during a 90 minute run at sustained speed. Resting values are compared with controls comprising 10 sedentary subjects. Runners show a significantly accelerated basal gastric emptying (runners t 1/2 = 67.7 (5.9) min; sedentaries t 1/2 = 85.3 (4.5) min, p less than 0.001). The exercise had no significant effect on gastric emptying in these trained subjects (exercise t 1/2 = 66.8 (5.9) min, p = NS), suggesting adaptation to exercise.

Validation of transport measurements in skeletal muscle with N-13 amino acids using a rabbit isolated hindlimb model

We are studying the transport of C-11 and N-13 labeled amino acids in tumor-bearing rabbits to determine the role of amino acid transport in the pathogenesis of muscle wasting in cancer. To validate a new, in vivo, method for measuring transport in skeletal muscle with these compounds, an isolated hindlimb model was developed in rabbits. The limb was perfused with a non-recirculating, normothermic, constant pressure system and a cell-free perfusate. Hemodynamic and metabolic parameters were measured during the first 75 min. of pergusion and found to remain normal and stable. Flow varied directly with perfusion pressure over the normal range of resting flows in the intact rabbit hindlimb. Time-activity curves (TAC's) were recorded from the medial thigh following bolus co-injection of L-[amide N-13] glutamine or N-13 L-glutamate with Tc-99m human serum albumin (HSA) into the femoral artery. Regional plasma flow was determined from the Tc-99m data. The N-13 TAC's consistently manifested a three-phased washout with half times of approximately 30 sec., 5 min. and 2 hr. Capillary and cellular transport parameters were computed from the N-13 data using a double barrier, single capillary model of capillary and cellular transport and assuming that the three washout components result, respectively, from tracer throughput, extraction into the interstitial space and extraction into the intracellular space. This interpretation was validated and the sensitivity of the technique to transport processes demonstrated by examining the effects on the N-13 TAC's and computed transport parameters of several factors known to influence cellular transport of amino acids, viz., the insulin concentration, amino acid concentration and pH of the perfusate. Time-activity curves and transport parameters for N-13 L-glutamine in the isolated limb were very similar to those observed in the intact rabbit hindlimb, suggesting that studies in the perfused model are indicative of amino acid transport in vivo. The methodology described here is especially well suited for studying the specific effects on transport of factors which influence amino acid metabolism in skeletal muscle (e.g., hormones and monokines).

Lung uptake of 131I-metaiodobenzylguanidine in sheep. An in vivo measurement of pulmonary metabolic function.

Circulating biogenic amines are known to be cleared by the mammalian lung. Their lung uptake is considered as an indicator of pulmonary endothelial integrity. Unfortunately, their use as markers of pulmonary metabolic function in human pathology is precluded by their biological effects and by the type of radiolabeling (3H and 14C), making them harmful for repeat injections and unfit for scintigraphy. Metaiodobenzylguanidine (MIBG) is structurally related to the neuron blocking agent guanethidine, devoid of significant biological effects, and has been shown to be extracted by the same active sodium dependent, saturable transport as norepinephrine in perfused rat lungs in vitro. We studied the single pass lung extraction of 131I-MIBG in five awake and five anaesthetised sheep using the standard double indicator dilution technique with 99mTc-human serum albumin (HSA) as an intravascular reference tracer. Intravenous bolus injection of increasing doses of MIBG up to 400 nmol resulted in a significant (F ratio = 7.778, P less than 0.0001) dose dependent decrease of MIBG extraction in both awake and anaesthetised sheep, without significant differences of extraction values between the two groups. For the 10 sheep, the averaged percentage single pass pulmonary uptake of MIBG at the peak of the dilution curve decreased from 32% +/- 3% (mean +/- SE, n = 27 measurements) with 20 nmol to 18% +/- 2% (n = 32) with 400 nmol. Estimates of the apparent Michaelis-Menten constant (Km) averaged 2 +/- 1.2 microM (n = 7), whereas estimates of the apparent maximum velocity of removal (Vmax) was 1.1 +/- 0.5 mumol/min (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Radiolabeled antibodies, albumin and antimony sulfide colloid: A comparison as lymphoscintigraphic agents

The kinetics of lymph node and systemic uptake of members of three different classes of lymphoscintigraphic agents were studied in normal laboratory rats. 99mTc antimony trisulfide colloid (TcSbC), 99mTc human serum albumin (TcHSA), 125I 5G6.4 (a murine IgG2ak monoclonal antibody), 125I 763.24T (a murine IgG 1), and 125I FT166 (a murine IgM monoclonal) all current or potential lymphoscintigraphic agents, were injected subcutaneously into the hind foot pads of healthy rats. Ipsilateral and contralateral popliteal lymph nodes were sampled up to 4 h post-injection. Subcutaneous injection resulted in far higher nodal uptake for all agents than i.v. delivery with ipsilateral popliteal node/blood ratios 1 h postsubcutaneous injection of: for TcSbC (1900)> 125I IgM (497)>TcHSA (72)> 125I Intact IgG2a or 125I IgG 1 at approximately 10. Thus, while all agents achieve popliteal node/blood ratios far greater than unity, TcSbc has the greatest absolute and relative nodal accumulation, greater than the 125I IgM monoclonal antibody and TcHSA. Uptake of the intact 125I IgG antibodies is lowest. These data suggest that TcSbC in particular, as well as TcHSA and IgM may be most useful as non-specific nodel imaging agents, while the lower background activity of the IgGs may make targeting specific antigen in nodes more feasible.