Radionuclide Injection Research Articles

Fluctuation of adenosine concentration by modes of intravenous infusion based on mathematical simulation and experiments

Adenosine, which has been used for a myocardial perfusion scan, shows rapid clearance from blood because of its short half-life of <10 seconds. This simulation study evaluates influences of modes of radionuclide injection on ventricular adenosine concentration when one intravenous injection line is used. Assuming that radionuclide injection is a unit impulse, time-activity curves were measured in the left ventricle (LV) and fitted by a gamma function. Typical patterns of concentration fluctuation when adenosine infusion was temporarily modified were calculated by the convolution integral of input function and unit impulse response. Variation of concentration was measured by experiments using continuous 99mTc injection and co-infusion of water via a three-way stopcock. Modes of co-infusion with various infusion speeds and volumes were examined. Intermission of adenosine infusion and rapid displacement by radionuclide co-injection significantly influenced the adenosine concentration in LV. Intermission of adenosine infusion for 2 seconds caused a 15% decrease in the adenosine concentration in the left ventricle. When a square-shaped input was assumed, a three-fold higher concentration of adenosine for 3 seconds created by radionuclide injection resulted in a +42% increase in the LV concentration. Based on a measured input function, radionuclide injection using three-way stopcock through one route caused a two- to three-fold increase in the steady concentration in the vein just after injection. When 0.5 ml of radionuclide was slowly co-injected, with three ways opened, it caused a relatively low fluctuation, creating a +34% to -47% change in concentration of LV. A flush of radionuclide with physiological saline significantly increased the adenosine concentration in LV, when short half-lives were assumed. An intravenous adenosine and radiopharmaceutical injection in the same line is feasible. However, the fluctuation of concentration depends significantly on the mode of injection. To minimize the fluctuation, a slow injection of a small volume of a myocardial imaging agent via a co-injection route, with three ways opened, is recommended.

Antecedent 99mTc-MDP and 99mTc-Sestamibi Administration Corrupts Bone Mineral Density Measured by DXA

Previous reports of the effect of antecedent administration of radionuclide on bone mineral density (BMD) measurements have yielded inconsistent results. Ten subjects scheduled for (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) bone scanning and 10 scheduled for (99m)Tc-sestamibi cardiac scanning had BMD measured by dual X-ray absorptiometry (DXA) (GE/Lunar) before and within 5 hours of diagnostic radionuclide injection. Paired t test and Wilcoxon-signed rank tests were used to compare the measured differences in BMD at multiple skeletal sites. Differences were subjected to multivariate analysis of demographic factors. Mean change in measured BMD following (99m)Tc-sestamibi administration (DeltaBMD-(99m)Tc-sestamibi) was -0.216+/-0.113 g/cm(2) at the total body and -0.348+/-0.300 g/cm(2) at the lumbar spine (p<0.005). Mean change in measured BMD following (99m)Tc-MDP administration (DeltaBMD-(99m)Tc-MDP) was -0.058+/-0.037 g/cm(2) at the total body and -0.053+/-0.049 g/cm(2) at the lumbar spine (p<0.05). Mean DeltaBMD-(99m)Tc-sestamibi exceeded least significant change (LSC) in all skeletal sites except the femoral trochanter. Mean DeltaBMD-(99m)Tc-MDP exceeded LSC only at the lumbar spine. The effect was correlated with (99m)Tc dose but not with gender, age, body mass index, baseline BMD, or time interval from injection to scan acquisition. In conclusion, BMD measured by the GE/Lunar Prodigy densitometer is corrupted by antecedent (99m)Tc-sestamibi and to a lesser extent by (99m)Tc-MDP. This effect is greater at the total body and lumbar spine than at the hip. Caution is warranted in scheduling and interpreting DXA studies when (99m)Tc has been recently administered.

Lymphatic Mapping and Sentinel Lymphadenectomy for 106 Head and Neck Lesions: Contrasts Between Oral Cavity and Cutaneous Malignancy

The objectives of this prospective series were to present our results in 106 sequential cases of lymphatic mapping and sentinel lymph node biopsy (SLNB) in the head and neck region and contrast the experience in oral cancer with that for cutaneous lesions. SLNB has an acceptably low complication rate in the head and neck. Lymphatic mapping and gamma probe-guided lymphadenectomy can improve the management of malignancies of the head and neck by more accurate identification of the nodal basins at risk and more accurate staging of the lymphatics. For appropriately selected patients, radionuclide lymphatic mapping may safely allow for minimally invasive sentinel lymphadenectomy without formal completion selective lymphadenectomy. One hundred six patients underwent intralesional radionuclide injection and radiologic lymphoscintigraphy (LS) on Institutional Review Board-approved protocols and 103 of these underwent successful SLNB. These included 35 patients with malignant melanoma, 10 cutaneous squamous cell carcinomas, four lip cancers, eight Merkel cell carcinomas, two rare cutaneous lesions, and 43 oral cancers. Mean follow up was 24 months. Patients with oral cavity malignancy underwent concurrent selective neck dissection after narrow-exposure sentinel lymph node excision. In this group, the SLNB histopathology could be correlated with the completion neck specimen histopathology. Patients with cutaneous malignancy underwent SLNB alone and only received regional lymphadenectomy based on positive histology or clinical indications. Data were tabulated for anatomic drainage patterns, complications, histopathology, and patterns of cancer recurrence. Surgical complications were rare. No temporary or permanent dysfunction of facial or spinal accessory nerves occurred with sentinel node biopsy. Lymphatic drainage to areas dramatically outside of the expected lymphatic basins occurred in 13.6%. Predictive value of a negative sentinel node was 98.2% for cutaneous malignancies (based on regional recurrence) and 92% with oral cancer (based on pathologic correlation). Gross tumor replacement of lymph nodes and redirection of lymphatic flow represented a significant technical issue in oral squamous cell carcinoma. Sixteen percent of patients with oral cancer were upstaged from N0 to N1 after extended sectioning and immunohistochemistry of the sentinel node. LS and SLNB can be performed with technical success in the head and neck region. Complications are minimal. More accurate staging and mapping of lymphatic drainage may improve the quality of standard lymphadenectomy. The potential for minimally invasive surgery based on this technology exists, but there is a small risk of missing positive disease. Whether the failure rate is greater than that of standard lymphadenectomy without gamma probe guidance is not known. New studies need to focus on refinements of technique and validation of accuracy as well as biologic correlates for the prediction of metastases.

Improving the Delivery of Radionuclides for Imaging and Therapy of Cancer Using Pretargeting Methods

The article reviews the background and current status of pretargeting for cancer imaging and therapy with radionuclides. Pretargeting procedures were introduced approximately 20 years ago as an alternative to directly radiolabeled antibodies. Because they were multistep processes, they were met with resistance but have since progressed to simple and improved procedures that could become the next generation of imaging and therapy with radionuclides. The separation of the radiolabeled compound from the antibody-targeting agent affords pretargeting procedures considerable flexibility in the radiolabeling process, providing opportunities for molecular imaging using gamma- or positron-emitting radionuclides and a variety of beta- and alpha-emitting radionuclides of therapeutic applications. Pretargeting methods improve tumor/nontumor ratios, exceeding that achieved with directly radiolabeled Fab' fragments, particularly within just a few hours of the radionuclide injection. In addition, tumor uptake exceeds that of a Fab' fragment by as much as 10-fold, giving pretargeting a greatly enhanced sensitivity for imaging. Advances in molecular biology have led to the development of novel binding proteins that have further improved radionuclide delivery in these systems. Studies in a variety of hematologic and solid tumor models have shown advantages of pretargeting compared with directly radiolabeled IgG for therapy, and there are several clinical studies under way that are also showing promising results. Thus, the next generation of targeting agents will likely employ pretargeting approaches to optimize radionuclide delivery for a wide range of applications.

Lymphatic Drainage Patterns on Early Versus Delayed Breast Lymphoscintigraphy Performed after Injection of Filtered Tc-99m Sulfur Colloid in Breast Cancer Patients Undergoing Sentinel Lymph Node Biopsy

The axillary lymph node status is the most important predictor of prognosis and aids in breast cancer treatment planning. Patients with breast cancer now frequently undergo sentinel lymph node (SLN) biopsy rather than axillary lymph node dissection to determine the status of the regional lymph nodes. However, the optimal timing of radionuclide injection relative to the timing of SLN biopsy remains controversial. The objective of this study was to compare the lymphatic drainage patterns on lymphoscintigraphy performed at 15 minutes to 4 hours and at 18 to 24 hours after injection of filtered Tc-99m sulfur colloid, and to determine whether, over time, radiocolloid migrates to second-echelon nodes that are not the SLNs. Fifteen women with breast cancer (mean age, 55 years; range, 38-78 years) were scheduled to undergo SLN biopsy after each received an injection of 18.5 MBq (0.5 mCi) filtered Tc-99m sulfur colloid into the breast parenchyma surrounding the tumor or biopsy cavity. Both early (15 minutes to 4 hours after radionuclide injection) and delayed (18-24 hours after radionuclide injection) lymphoscintigraphy was performed in each patient. SLN biopsy was performed, followed by completion axillary lymph node dissection and planned breast surgery. In each patient the patterns of distribution of the radionuclide in the lymph nodes were the same on early and delayed lymphoscintigrams. These findings, that the distributions of radionuclide in lymph nodes are identical on early and delayed images obtained after injection of filtered Tc-99m sulfur colloid, suggest that performing SLN biopsy on the day after injection does not diminish the accuracy of the technique in predicting the potential site of metastasis in the regional lymph nodes in patients undergoing this procedure for breast cancer.

A training simulator for sentinel node biopsy in breast cancer: a new standard

Background Sentinel node biopsy is becoming the staging investigation of choice for early breast cancer. Optimal identification of the sentinel node requires the utilization of a radionuclide in combination with blue dye. Gamma probe guided surgery is a skill that is currently unfamiliar to many surgeons. Appropriate training within the surgical skills laboratory could play a major role in the widespread implementation of this technique, but no suitable model currently exists for this purpose. Aim To develop a realistic phantom for the teaching and practice of the core new skills required of a surgeon to perform gamma probe guided sentinel node biopsy in breast cancer. Methods We describe the development of our sentinel node biopsy simulator which consists of a torso with its arm extended in an operating position. The replaceable breast and axilla are constructed from a thermoplastic elastomer gel, which has similar physical and radiation attenuation properties to that of human tissue. Radionuclide injection sites and radioactive sentinel nodes are simulated by hollow blue coloured PVC beads filled with Technetium-99m. The model allows demonstration and practice of injection techniques, imaging techniques and gamma probe guided removal of sentinel nodes. Conclusion We believe that training for sentinel node biopsy should begin in the surgical skills laboratory. The model we have developed is able to provide an accurate simulation of all new practical skills required for accurate sentinel node identification. It is an important aid to training in the sentinel lymph node biopsy procedure for breast carcinoma.

Does soft tissue cancer affect the development of radionuclide-induced skeletal malignancy?

Data in the archives of the beagle project at the University of Utah were used to determine whether there might have been an association between the occurrence of soft tissue cancer and bone tumor (skeletal malignancy) among the dogs injected with bone-seeking radionuclides. In addition to comparing the numbers of animals with and without bone tumors and with and without soft tissue cancers, data on bone sarcomas and soft tissue sarcomas were compared. Longevity (postinjection survival) of the dogs was investigated. It appeared that survival (time between radionuclide injection and death) was important in the eventual expression of malignancies. There could not be established a possible susceptibility to skeletal malignancy associated with the occurrence of soft tissue cancer (or soft tissue sarcoma). We concluded that, although the literature reports an increased susceptibility for subsequent malignancies for individuals with naturally-occurring or radiation-induced cancer, the data derived from this study do not confirm the concept that the appearance of soft tissue cancer is strongly associated with an increased risk of developing a radionuclide-induced skeletal malignancy.

Immediate Preoperative Injection of 99m-Tc Sulfur Colloid Is Effective in the Detection of Breast Sentinel Lymph Nodes

Sentinel lymph node (SLN) biopsy is an accurate technique to determine the metastatic status of lymph nodes. Radionuclide guidance makes the procedure easier and improves the success rate. Coordinating the operating room and nuclear medicine schedules causes delays when same-day radionuclide injection is used. We hypothesized that injection of 99m-Tc sulfur colloid immediately preoperatively is effective in SLN detection. We analyzed a prospective database of 70 patients treated at Harbor-UCLA Medical Center. The first 39 patients underwent completion axillary dissection (Group A) and subdermal injection of sulfur colloid immediately before surgery. A second group of 31 patients (Group B) had intraparenchymal injection immediately before surgery. We used isosulfan blue in all cases. SLNs were identified in 97 per cent of cases. SLNs were radioactive in 94 per cent and blue in 90 per cent. In Group A the accuracy and the positive and negative predictive values of SLN biopsy were 100 per cent. SLN counts per second ranged from 22 to 1700. The mean count per second was 290 ± 281 (mean ± standard deviation). Subdermal and intraparenchymal injections were equally successful (93% vs 92%). In conclusion injection of radiocolloid and isosulfan blue immediately preoperatively is highly successful and accurate in the detection of SLNs in breast cancer. It avoids operating room schedule delays.

The Excavation Project in the Grimsel Test Site: In Situ High-Resolution Gamma and Alpha Spectrometry of 60Co, 75Se, 113Sn, 152Eu, 235U, and 237Np/233Pa

ABSTRACTFull excavation of a water-conducting shear zone used for radionuclide migration experiments is part of a comprehensive study to physically determine the sites of in-situ radionuclide retardation. Prior to the excavation, multi-tracer solutions containing strongly sorbing y- and αemitting nuclides were injected into the shear zone and the water extracted was analyzed on-line using in situ, high-resolution y-spectrometry. In addition, water samples were collected to compare quantitatively the on-line data with subsequent laboratory measurements α- and γ- spectrometry) and also to analyze samples with activities below the detection limits of the in-situ analysis. The breakthrough curves indicate that Se had passed through the fracture with a velocity comparable to a conservatively behaving dye (uranine), but very strong retardation of Co. Eu and Sn was observed. The recoveries of these nuclides were found to be in the order of only a few percent when the dipole flow-field was interrupted about one month after radionuclide injection and the fracture was sealed off for excavation. Significant retardation was also obtained for the oxemitters U, Np and Pa. Almost identical breakthrough curves for these actinides were measured, suggesting a similar spatial distribution in the fracture at any given time.

Diuresis Renography

In 20 patients investigated for unilateral upper urinary tract obstruction diuresis renography was performed simultaneously with 131I-hippuran and 99Tcm-MAG3 using a gamma camera with dual isotope facilities. Furosemide was administered routinely 20 min after radionuclide injection. No significant differences were found in fractional share between the two kidneys, time to maximal activity, residual activity at 20 and 30 min, or rate of emptying after furosemide administration. The MAG3 curves showed, however, better counting statistics and on scintigrams with MAG3 more anatomic details (extent of dilation and site of obstruction) could be seen. It is concluded, that MAG3 is superior to hippuran in the evaluation of patients with possible unilateral upper urinary tract obstruction by diuresis renography.

Diuresis Renography

In 20 patients investigated for unilateral upper urinary tract obstruction diuresis renography was performed simultaneously with 131I-hippuran and 99Tcm-MAG3 using a gamma camera with dual isotope facilities. Furosemide was administered routinely 20 min after radionuclide injection. No significant differences were found in fractional share between the two kidneys, time to maximal activity, residual activity at 20 and 30 min, or rate of emptying after furosemide administration. The MAG3 curves showed, however, better counting statistics and on scintigrams with MAG3 more anatomic details (extent of dilation and site of obstruction) could be seen. It is concluded, that MAG3 is superior to hippuran in the evaluation of patients with possible unilateral upper urinary tract obstruction by diuresis renography.

Effect of ischemia and postischemic dysfunction on myocardial uptake of technetium-99m-labeled methoxyisobutyl isonitrile and thallium-201

The myocardial uptake of a new technetium-99m-labeled myocardial perfusion agent, methoxyisobutyl isonitrile (Tc-99m MIBI), and thallium-201 was correlated with microsphere flow in an open chest canine model of low coronary flow and postischemic dysfunction. Eighteen dogs were given an injection of thallium-201 (0.5 mCi) and Tc-99m MIBI (5 mCi) either after 40 min of partial left anterior descending artery occlusion (Group I, 10 dogs) or during reperfusion after 15 min of left anterior descending artery occlusion (Group II, 8 dogs). Regional dysfunction was documented during injection in both groups by quantitative two-dimensional echocardiography. Regional blood flow was assessed by radiolabeled microspheres. The heart was excised 15 min after radionuclide injection and the left ventricle divided into 96 segments for gamma well counting.Among Group I dogs, central ischemic thallium-201 and Tc-99m MIBI activity (expressed as a percent of the activity in the corresponding nonischemic zone) was comparable, respectively, for endocardial (54 ± 17% and 52 ± 17%), mid-wall (71 ± 20% and 69 ± 17%) and epicardial (89 ± 13% and 94 ± 9%) segments and increased proportionally with flow. There was a good linear correlation among these endocardial segments between flow and both thallium-201 (r = 0.78) and Tc-99m MIBI (r = 0.85) activity. Among Group II dogs, central ischemic endocardial flow (59 ± 14%) was comparable to thallium-201 (70 ± 18%) and Tc-99m MIBI (74 ± 12%) activity. Similarly, relative endocardial flow in the intermediate ischemic region (71 ± 11%) was comparable to thallium-201 (77 ± 11%) and Tc-99m MIBI (81 ± 10%) activity.Thus, myocardial uptake of Tc-99m MIBI and thallium-201 is comparable under conditions of low coronary flow and postischemic dysfunction and closely parallels flow alterations.

Isotope Transport Studies and Shunt Pressure Measurements as a Guide to Shunt Function

Shunt function testing by radionuclide injection and shunt pressure measurement was performed in 312 cases. In our experience the test has a sensitivity of 92% and accuracy of 89%. The diagnostic value of the components of the test are discussed. The test is a safe and integral part of the assessment of shunt function. The significance of shunt malfunction must of course be determined by clinical evaluation, measures of ventricular size by CAT scanning or ultrasound, and by continuous ICP recording. However the shunt function test combined with shunt pressure measurement is a safe and essential investigation of symptomatic shunt malfunction.

Studies on the lysosomal binding of 141Ce, 239Np, 239Pu and 241Am in rat and syrian hamster liver using carrier-free electrophoresis

The binding of 141Ce, 239Np, 139Pu and 241Am in the liver of rats and Syrian hamsters, following injection in essentially monomeric form, was analyzed by carrier-free electrophoresis at 4–9 days and several months after radionuclide injection. In contrast to density gradient methods lysosomes can be clearly separated from other cell organelles by carrier-free electrophoresis. These, and previous results from this and other laboratories confirm that lysosomes are the main initial binding site for these four radionuclides in the livers of rats and Syrian or Chinese hamsters. Light microscopic autoradiography showed that at all the time intervals studied 241Am was more or less uniformly distributed in the liver of all three species. Thus, the changes in the electrophoretic pattern of the nuclides, observed at later time periods in hamsters, cannot be explained by gross redistribution phenomena such as accumulation in macrophages.

The retention of metallic radionuclides in experimental abscesses in rats

The retention of 67Ga, 203Hg, 175 + 181Hf, 239Pu and 241Am in turpentine-induced abscesses and in normal muscle has been studied in rats for periods of up to 126 days after radionuclide injection (129 days after turpentine). The results show that although the uptake of 203Hg is about 7 times greater in the abscess than in control muscle, the half time of the nuclide is similar in both tissues, T1/2 = 5 days. The remaining radionuclides studied all show a similar retention time in control muscle, average T1/2 = 12.5 days, and a more prolonged retention in the abscess tissue, average T1/2 = 47 days, although in both control and abscess tissue the uptake of the radionuclides showed quite large metal-specific variations. It is concluded that for radionuclides which are transported on transferrin in the blood and which deposit in lysosomes within cells a common metal clearance mechanism may operate in normal muscle and a second general mechanism may operate in abscess tissue. The radionuclide concentration difference between normal and abscess tissue ranged from 8 (67Ga) to 27 (239Pu); thus the radiation dose delivered to the inflamed tissue was between about 30 and 100 times greater than in normal muscle.

Effect of Age on the Efficacy of Zn-Diethylenetriaminepentaacetic Acid Therapy for Removal of Am and Pu from Beagles

Decorporation of intravenously injected monomeric 241Am and 237+239Pu by the administration of 30 mumole Zn-diethylenetriaminepentaacetic acid (DTPA)/kg each day beginning 2 weeks after radionuclide injection was compared in beagles entered into the experiment when 3 months (juveniles). 1.9 years (young adults), or 10 years (mature adults) old and studied for about 5 months. DTPA therapy was most effective in the juvenile dogs and least effective in the mature adults. Retention of 241Am in the liver decreased from a pretreatment value for adults of about 50% of the injected activity to about 10% in the mature adults and less than 1% in the young adults at 140 days of treatment, while the liver retention of juveniles decreased from pretreatment values of about 16% to undetectable levels by 28 days of treatment. Plutonium retention in the liver decreased from adult pretreatment levels of about 30% of the injected activity (corrected for radioactive decay) to near 10% in the mature adults and 6% in the young adults at 140 days of treatment, while juvenile liver retention decreased from pretreatment values near 15% to undetectable levels by 56 days of treatment. Nonliver Am retention (mainly skeleton) decreased in mature adults from pretreatment values of about 45% of the injected activity to near 25%, in young adults from 35 to 20%, and in juveniles from roughly 70 to 9% by 140 days of DTPA administration. Nonliver Pu retention decreased from pretreatment values of about 50% of the injected activity (corrected for radioactive decay) for mature and young adults to about 30% by 140 days and from 75 to 16% in juveniles over the time period.

The use of three-phase radionuclide bone scanning in the diagnosis of reflex sympathetic dystrophy

One hundred forty-five consecutive three-phase radionuclide bone scans were reviewed. One hundred two of these were performed to evaluate pain in the hand. Of these, 23 patients clinically had reflex sympathetic dystrophy (RSD). The hand scans were performed by the three-phase technique. Phase I is a radionuclide angiogram. Phase II is the blood pool or tissue phase. Phase III consists of delayed images obtained 3 to 4 hours after radionuclide injection. Detailed analysis of the 145 three-phase radionuclide bone scans of the hand demonstrated that the diffuse increased tracer uptake in the delayed image (phase III) is diagnostic for RSD, with a sensitivity of 96% and a specificity of 98%. The two early phases (radionuclide angiogram and blood pool) were positive in only 45% and 52% of the RSD patients, respectively. The strictly interpreted delayed radionuclide image is extremely sensitive in the diagnosis of RSD and will facilitate the early diagnosis and subsequent treatment of this syndrome.

Differences between 201T1 and 43K Tissue Distribution in Rested and Exercised Rats

A comparison is made of relative organ-to-plasma uptake of 43K and 201Tl in rats at rest and after exercise (two hour swimming). Organs were obtained 0.5 or 3 hrs after radionuclide injection. Thus, there were four groups each for 43K and 201 Tl. For 201Tl the triad kidneys-heart-adrenals was very consistent throughout the four experimental situations in showing the highest uptake, whereas for 43K adrenals-heart-liver predominated at 0.5 hrs and thymus-liver at 3 hrs. The ratio 201Tl/43K in myocardium was always greater than unity in all four experimental situations. The heart-to-lung and heart-to-liver uptake ratios were lower in all cases for 43K vs. 201Tl. One of the most important findings was that exercise always determined an increase of these ratios for 201Tl, but it had an unfavorable effect on the 43K heart/lung ratio and no definite effect on the 43K heart/liver ratio. Our findings are analyzed in the light of previous publications. It is concluded that these two ions have biologically important different characteristics and that excessive and seemingly unjustified emphasis has been made on their physiological similarity.

Effect of salmon calcitonin infusion on plasma concentrations of recently administered 45Ca.

The effect of intravenous salmon calcitonin (SCT) infusion on the net rate of loss from plasma of recently injected45Ca has been studied in conscious fasted rats, some of which had been previously thyroparathyroidectomized (TPTX). The45Ca was injected 10 h prior to or 1 or 2 h after the initiation of the infusion. Salmon calcitonin (0.05–0.2 MRC mU/g body weight/h) infusion produced the expected hypocalcemia and hypophosphatemia. The drop in plasma calcium levels produced by the hormone was lowered further by the addition of phosphate to the infusate. Plasma45Ca changes, during SCT infusion, followed a biphasic pattern when the radionuclide injection preceded SCT infusion by 10 h. During the first part of the infusion, the rate of loss of45Ca from plasma was greater in SCT-treated than in control rats. Later, this pattern reversed, and the rate of loss of45Ca from plasma became slower in SCT-treated animals. If45Ca was injected after SCT infusion was initiated only the second phase of the biphasic effect was observed; i.e., disappearance of45Ca from plasma was slower in SCT-infused than in control rats. These data are considered to support the hypothesis that rapid and opposing calcium fluxes exist between bone fluid and plasma, and that calcitonin acts by decreasing the calcium efflux from bone fluid. The calcium moved in this efflux system includes some that has only recently entered bone fluid from plasma. This is the explanation given for the initial decrease in plasma45Ca concentrations following SCT infusion. The reverse effect in the second phase can be explained as the result of a secondary reduction in calcium influx to bone fluid from plasma.

Scintiangiocardiography in children: Rapid sequence visualization of the heart and great vessels following intravenous radionuclide injection

Scintiangiocardiography in children: Rapid sequence visualization of the heart and great vessels following intravenous radionuclide injection