Technetium-99m DTPA uptake and transit in bone: effect on blood clearance in rabbits

The purpose of this study is to explain the initial "plateau" distribution of [99mTc]DTPA in the forearm found when using serial external counting for kidney clearance measurements. A study by a MIRD task group, McAfee et al. 1979 (1), measured the biologic distribution of [99mTc]DTPA(Sn) in most body tissues but omitted bone, which we believe is a major contributor to this initial "plateau". Using MIRD criteria, measurements were carried out on rabbit humeri and these were compared with results obtained from human subjects. It would appear that initial accumulation of the compound by interstitial bone is the reason for the "plateau" and explains why blood sampling for GFR studies should not be undertaken over the first 2 hr. In addition, the results of this study provide valuable information relevant to bone perfusion studies and the biologic distribution and concentration of i.v. administered drugs during the first 2 hr postinjection.     

Differences between 99mTc-sestamibi and 99mTc-tetrofosmin uptake in thyroid and salivary glands: comparison with 99mTc-pertechnetate in 86 subjects

Tc-tetrofosmin seems to show a prolonged thyroid retention when compared with Tc-sestamibi; this may explain its poorer performance in the dual-phase parathyroid scintigraphy. In order to verify objectively whether and to what extent Tc-sestamibi and Tc-tetrofosmin uptake and retention differ in the thyroid gland, we performed a head-to-head comparison between the tracers in 86 euthyroid subjects enrolled in five centres. Data were compared with those of Tc-pertechnetate obtained from the same subjects. For comparison purposes, quantitative data from the salivary glands were also obtained. Tc-sestamibi showed a higher early thyroid uptake (2.26+/-0.52 vs. 2.01+/-0.49, respectively; P<0.002) and a lower retention (1.4+/-0.37 vs. 1.65+/-0.58, respectively; P<0.002) when compared with Tc-tetrofosmin. This finding provides an objective basis for the poorer results of Tc-tetrofosmin in dual-phase parathyroid scintigraphy. Delayed Tc-tetrofosmin salivary gland uptake was unexpectedly high and approached the Tc-pertechnetate value (2.29+/-0.56 vs. 2.46+/-0.75, respectively; P =not significant). This finding should be kept in mind in order to avoid interpretation pitfalls in thyroid and parathyroid imaging with Tc-tetrofosmin, as well as in other oncological imaging of the neck region. This study definitely establishes that Tc-tetrofosmin and Tc-sestamibi are not twin but rather sibling tracers.     

Adenocarcinoma of the lung with marked uptake of 99mTc-pertechnetate: case report.

Following biopsy of a hilar mass, a heart scan performed with 99mTc-pertechnetate showed intense uptake in the mass. The degree of radionuclide concentration suggested that the mass was glandular tissue, most likely an adenoma or adenocarcinoma. Biopsy revealed a mucinsecreting adenocarcinoma. Review of the literature showed examples of active glandular concentration of pertechnetate in the thyroid, gastric mucosa, breast, lacrimal glands, and colon. This case provides an example of reasoning by which the scan interpretation came closer to the actual tissue diagnosis than is usually possible.     

99mTc-pertechnetate uptake in hepatoma cells due to tissue-specific human sodium iodide symporter gene expression

The sodium iodide symporter (NIS) gene could be used as an ideal reporter gene as well as a promising therapeutic gene. 99mTc-pertechnetate has proven to be more advantageous than 131I-iodide with respect to image quality, procedure and radiation dose in examination of thyroid uptake and scintigraphy. Herein, we investigated the feasibility of monitoring human sodium iodide symporter (hNIS) gene expression with 99mTc-pertechnetate in hepatoma cells (MH3924A) following tissue-specific expression. METHODS: MH3924A cells were stably transfected with the recombinant retroviral vector, in which hNIS cDNA was driven by murine albumin enhancer/promoter (mAlb) and coupled to hygromycin resistance gene using an internal ribosomal entry site. Functional NIS expression in hepatoma cells was confirmed by an 125I(-) uptake assay. The dynamic uptake and efflux of 99mTc-pertechnetate was determined both in vitro and in vivo. RESULTS: The 99mTc-pertechnetate was up to 254-fold higher in stably transfected MH3924A cells than in wild-type cells. However, the in vitro efflux of 99mTc-pertechnetate out of recombinant cells was rapid with a half-life of less than 2 min. Further, the in vivo studies yielded clear images and quantitative data of mAlbhNIS-infected tumor xenografts using 99mTc-pertechnetate and gamma camera. CONCLUSION: The current study demonstrates enhanced 99mTc-pertechnetate uptake in hepatoma cells in vitro and in vivo following tissue-specific gene transfer using a recombinant retrovirus with the albumin enhancer/promoter and the hNIS gene. It is feasible to monitor hNIS gene expression noninvasively and quantitatively using conventional gamma camera and 99mTc-pertechnetate.     

Simple, rapid thyroid function testing with 99mTc-pertechnetate thyroid uptake ratio and neck/thigh ratio.

To avoid the technical difficulties and errors inherent in the measurement of early thyroid uptake of 99mTcO4-,techniques which are independent of absolute uptake, neck extrathyroidal background and dose standards were evaluated in a series of 108 patients. After intravenous injection of 2 mCi 99mTcO4-, radioactivity was recorded over the neck and thigh. Thyroid uptake ratios were calculated as the ratios of activity over the neck at two times. A neck/thigh ratio was calculated from the recorded activities at 15 min after injection. Examination of these parameters showed that a combination of the 15 min neck/thigh ratio and the 10'/2' thyroid uptake ratio best served to discriminate thyroid function: 92% of hyperthyroid cases were correctly identified by a neck/thigh ratio above 4.7 and 95% of hypothyroid cases were identified by the combination of a neck/thigh ratio below 3 and a 10'/2' thyroid uptake ratio below 1. Correct classification of euthyroidism was 84% but with the exclusion of patients previously treated with 131I, this rose to 91%. The accuracy of the 99mTc procedure is comparable to that of the standard 24 hr 131I uptake run concurrently in this series and duplicates the accuracy of computer assisted determinations of absolute thyroid 99mTcO4- uptakes. The procedure provides a convenient method for the evaluation of thyroid function as an accompaniment to 99mTcO4- thyroid imaging.     

Secondary lymphoma of the thyroid in 99mTc-pertechnetate scintigraphy

We present markedly decreased radioactivity in the right on a ^99mTc-pertechnetate thyroid image in a patient with secondary lymphoma of the thyroid. At autopsy, the right lobe of the thyroid was replaced by lymphoma tissue. Markedly decreased radioactivity on the images may be explained by lymphoma cell infiltration or replacement of thyroid tissue with a resultant attenuation effect as well as interference of the trapping mechanism of the thyroid folicular cell. While cold areas in a radionuclide scintigram may present difficulties in interpretation, a high index of secondary lymphoma suspicion should be made by a combination of the scintigraphic findings and history of malignant lymphoma.Supported in part by Biomedical Research support Grant No. RR 05374 from Biomedical Research Support Branch, Division of Research Facilities and Resources, NIH     

Evaluation of the renal clearance of technetium-99m PAHIDA in dogs

The renal clearance of the technetium-99m complex of para[(biscarboxylmethyl)-aminomethylcarboxyamino]hippuric acid ([99mTc]PAHIDA), has been previously studied in rodents and falls between that of [99mTc]DTPA (diethylenetriaminepentaacetic acid) and iodine-131 (131I) orthoiodohippuran (OIH). To investigate the effect of species variation, the plasma clearance of [99mTc]PAHIDA was investigated in dogs. The plasma disappearance of the renal agent approached that of [99mTc]DTPA and was significantly less than that of OIH. Despite the structural similarities of the PAHIDA ligand and aminohippurate, the [99mTc]PAHIDA complex undergoes little, if any, tubular secretion in the canine kidney.     

Myocardial accumulation and clearance of technetium 99m teboroxime at 100%, 75%, 50% and zero coronary blood flow in dogs

Sequential changes in the regional distribution of technetium 99m Teboroxime (SQ30217) were evaluated in nine dogs with graded coronary artery stenosis, occlusion and reperfusion of either the left anterior descending or left circumflex arteries. 99mTc-Teboroxime accumulation recorded by planar imaging was compared with directly measured coronary blood flow (Doppler) and regional myocardial perfusion (microspheres). Serial images were recorded beginning at the time of injection and continuing for the next 18 min. The data were summed from minutes 2-3, 3-6, 4-8 and 9-18 after injection for comparison with the other parameters. Myocardial clearance of Teboroxime was analysed at each level of blood flow. There was a linear relationship between the Teboroxime activity ratio (abnormal/normal) and coronary blood flow (r = 0.96) and regional myocardial perfusion (r = 0.99). Zones of diminished perfusion were least apparent in the summed images recorded during minutes 2-3. In later images, the lesions were well visualized. The myocardial clearance half-times at 100%, 75% and 50% flow were not significantly different, while clearance half-time at total occlusion was significantly (P less than 0.01) faster. In the 3-6, 4-8 and 9-18 minutes summed images, the Teboroxime activity ratio increased significantly (P less than 0.01) after reperfusion compared with total occlusion.     

Myocardial accumulation and clearance of technetium 99m Teboroxime at 100%, 75%, 50% and zero coronary blood flow in dogs

Sequential changes in the regional distribution of technetium 99m Teboroxime (SQ30217) were evaluated in nine dogs with graded coronary artery stenosis, occlusion and reperfusion of either the left anterior descending or left circumflex arteries. ^99mTc-Teboroxime accumulation recorded by planar imaging was compared with directly measured coronary blood flow (Doppler) and regional myocardial perfusion (microspheres). Serial images were recorded beginning at the time of injection and continuing for the next 18 min. The data were summed from minutes 2–3, 3–6, 4–8 and 9–18 after injection for comparison with the other parameters. Myocardial clearance of Teboroxime was analysed at each level of blood flow. There was a linear relationship between the Teboroxime activity ratio (abnormal/normal) and coronary blood flow (r=0.96) and regional myocardial perfusion (r = 0.99). Zones of diminished perfusion were least apparent in the summed images recorded during minutes 2–3. In later images, the lesions were well visualized. The myocardial clearance half-times at 100%, 75% and 50% flow were not significantly different, while clearance half-time at total occlusion was significantly (P < 0.01) faster. In the 3–6, 4–8 and 9–18 minutes summed images, the Teboroxime activity ratio increased significantly (P < 0.01) after reperfusion compared with total occlusion. Offprint requests to: H.W. Strauss     

Secondary lymphoma of the thyroid in 99mTc-pertechnetate scintigraphy

We present markedly decreased radioactivity in the right on a 99mTc-pertechnetate thyroid image in a patient with secondary lymphoma of the thyroid. At autopsy, the right lobe of the thyroid was replaced by lymphoma tissue. Markedly decreased radioactivity on the images may be explained by lymphoma cell infiltration or replacement of thyroid tissue with a resultant attenuation effect as well as interference of the trapping mechanism of the thyroid folicular cell. While cold areas in a radionuclide scintigram may present difficulties in interpretation, a high index of secondary lymphoma suspicion should be made by a combination of the scintigraphic findings and history of malignant lymphoma.