Tc-99m Agents Research Articles

Adherence of Tc-99m agents to plastic syringes

Adherence of Tc-99m agents to plastic syringes

In Vitro Evaluation of Tc-99m Radiopharmaceuticals for Gastric Emptying Studies

Objective: Gastrointestinal motility and functional motility disorders causing either delayed or accelerated gastric emptying (GE) may result in similar symptoms including nausea, vomiting, early satiety, fullness, bloating, and abdominal discomfort or pain. Hence, it is important to evaluate patients for both rapid and delayed GE in the same test. The gold standard technique to measure GE is scintigraphy by radiolabeled test meals. The aim of this study was to test alternative Tc-99m agents to label eggs as the solid meal and compare to Tc-99m sulfur colloid (SC) for gastric emptying studies.Methods: In search of alternative agents for gastric emptying studies, we mixed and fried eggs with four different particulate compounds (Tc-99m labeled SC, tin colloid, nanocolloid and MAA), as well as with free pertechnetate and Tc-99m DTPA. We then measured the stability of these compounds in simulated gastric juice.Results: Our experiments demonstrated that in addition to Tc-99m sulfur colloid;Tc-99m MAA, Tc-99m nanocolloid and Tc-99m tin colloid also appear to make stable complexes with eggs in acidic environment.Conclusion: Therefore, these agents may be used for gastric emptying studies which could be more practical in routine conditions.Conflict of interest:None declared.

117: Direct comparison of stress Thallium-201/Rest Technetium-99m dual isotope perfusion imaging with Cadmium-Zinc-Telluride detector versus standard dual detector camera

Recent advances in nuclear myocardial perfusion imaging (MPI) have provided opportunity for improved image information with an important reduction of exam time and radiation. This technology can be used to explore novel protocols (dual isotope high-speed MPI). Today, two devices exist: D-SPECT and Discovery NM 530c (DNM) camera. With D-SPECT, it was showed that rapid stress Tl-201/rest Tc-99m protocol for use with high-speed MPI has offered the superior qualities of Tl-201 for stress imaging and of the Tc-99m agents for rest imaging can be preserved. However, no study has evaluated the same dual-isotope protocol with the other system. A total of 38 consecutive patients underwent simultaneous dual-radionuclide (stress thallium-201/rest technetium-99m) perfusion imaging with a DNM camera and standard dual dectector camera (S-SPECT) during the month of May 2011. All patients successfully underwent stress/rest MPI with both cameras. In 38 patients (50%) pharmacological stress was induced with dipyridamole. DNM SPECT SSS and SRS correlated linearly with conventional S-SPECT respective scores (r=0.84, p<0.0001 for SSS, and r=0.94, p<0.0001 for SRS). On Bland-Altman analysis there was good agreement between the two imaging methods with a shift for both SSS and SRS (mean difference = 1, 95% confidence interval = −3.74 – 5.74 for SSS; mean difference = −3.0, 95% confidence interval = −3.13 – 3.91 for SRS). The analyze revealed a perfusion defect in both the S-SPECT and DNM scans but systematically perfusionnels defects or scars were more extensive with the DNM-camera. Overall image quality was good to excellent. Our study showed a clinical agreement of 96% between the DNM camera and S-SPECT MPI. The effective dose was 11.9 mSv for the study protocol, with 9.7 mSv coming from the Tl-201. The DNM camera such as D-SPECT camera provides clinical information equivalent to conventional standard SPECT MPI.

Stress Thallium-201/Rest Technetium-99m Sequential Dual Isotope High-Speed Myocardial Perfusion Imaging

Our purpose was to describe a novel, rapid stress thallium-201 (Tl-201)/rest technetium-99m (Tc-99m) agent myocardial perfusion imaging (MPI) protocol (Tl/Tc) with a high-speed MPI scanner and to compare this protocol with a standard rest/stress Tc-99m agent protocol (Tc/Tc) with respect to image quality and radiation dosimetry. Recent advances in gamma camera technology have provided opportunity for improved SPECT MPI protocols. A rapid Tl/Tc protocol that could improve image information while maintaining a low radiation burden for the patient would be desirable. We compared high-speed SPECT MPI studies in 374 consecutive patients undergoing exercise or pharmacologic Tl/Tc protocol to those of 262 patients undergoing rest/stress Tc/Tc protocol. Tl/Tc imaging was accomplished in <20 min. Overall image quality was good to excellent in 96% and 98% of patients with the Tl/Tc and the Tc/Tc protocols, respectively (p = ns). Beginning rest imaging within 2 min after rest injection with the Tl/Tc protocol did not result in reduced confidence in image interpretation. Early rest Tc images of the Tl/Tc protocol showed less extracardiac activity than was observed on standard rest imaging used in the Tc/Tc protocol (84% vs. 61%), respectively (p < 0.01). The normalcy rate was high in both groups (100% vs. 92%). Radiation burden was similar between the Tl/Tc and Tc/Tc protocols. A rapid stress Tl-201/rest Tc-99m protocol for use with high-speed SPECT MPI has image quality and radiation dosimetry similar to those observed with a conventional rest/stress Tc-99m protocol. The Tl/Tc protocol offers promise as an efficient and relatively low radiation dose method, in which the superior qualities of Tl-201 for stress imaging and of the Tc-99m agents for rest imaging can be preserved. The findings also suggest that with rapid imaging rest MPI immediately after Tc-99m agent injection may be superior to standard delayed image initiation.

Abstract 5818: Stress Thallium-201/Rest Tc-99m Sequential Dual Isotope High-Speed Myocardial Perfusion Imaging

Recent advances in gamma camera technology are providing opportunities for novel high-speed myocardial perfusion imaging (HS-MPI) protocols. We aimed to develop and evaluate a stress thallium-201 (Tl-201) and rest Tc-99m sestamibi or tetrofosmin imaging protocol that could reduce imaging time and radiation burden. Methods: We studied 410 consecutive patients undergoing exercise or pharmacologic low-dose stress Tl-201 HS-MPI (4 min/acquisition) in the semi-upright and supine positions (D-SPECT, Spectrum-Dynamics) followed by rest Tc-99m sestamibi (n= 139) or tetrofosmin (n= 271) with immediate post-injection rest imaging. Of 330 patients with no known coronary artery disease (CAD), 29 patients also underwent invasive coronary angiography (ICA) or coronary computed tomography angiography (CCTA) within a three month period and 36 had a &lt; 5% pre-test likelihood of CAD (LLk). Despite low injected doses [Tl-201 (2.2± 0.3 mCi) and Tc-99m sestamibi or tetrofosmin (8.9± 2.4 mCi), the 3 acquisition MPI protocol (2 stress/1 rest) was accomplished &lt; 20 minutes. The quality of stress and resting image was good to excellent in &gt;96% of cases; importantly, no or minor extracardiac activity was seen on 99% of stress and 93% of rest images. HS-MPI was nondiagnostic or uninterpretable in only 2/410 patients. In the 29 patients with CCTA or ICA, the sensitivity and specificity for the detection of ≥70% stenosis were 73% and 89%, respectively, and in 15 patients with ICA, the sensitivity was 89%. The normalcy rate in the LLk group was 100%. A fast stress Tl-201/rest Tc-99m HS-MPI protocol offers promise as a time-efficient, low radiation dose method, in which the superior qualities of Tl-201 for stress imaging and of Tc-99m agents for rest imaging can be utilized.

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Comparison between Tc-99m N-NOET and Tl-201 in the assessment of patients with known or suspected coronary artery disease

Technetium 99m N-ethoxy-N-ethyl dithiocarbamate (N-NOET) is a new radionuclide tracer for cardiac single photon emission computed tomography (SPECT) imaging. It combines the advantageous properties of a Tc-99m agent with the redistribution characteristics of thallium 201. We directly compared the two agents in patients with known or suspected coronary artery disease. Fifty patients underwent treadmill exercise Tc-99m N-NOET and Tl-201 SPECT studies. Images were acquired at stress, redistribution, and reinjection. Segmental analysis was carried out, and direct comparisons were made with corresponding segments. A stress score index was calculated and compared with the degree of lung uptake for each patient. From the 50 patients, 2657 of 2664 exercise, redistribution, and reinjection segments (99%) were interpreted. There was excellent agreement between the two modalities (weighted kappa = 0.83). Of the patients, 24 demonstrated reversible ischemia by Tl-201 SPECT reinjection imaging, of which Tc-99m N-NOET stress-redistribution imaging correctly identified 14 (58%); this improved significantly to 20 patients (83%) ( P = .03) when a reinjection protocol was used. A higher stress score index was seen in those patients with significant lung uptake (lung-heart ratio > or =0.6) after Tc-99m N-NOET stress imaging (1.6 vs 1.3, P = .03). SPECT imaging with Tc-99m N-NOET is comparable to Tl-201 for the diagnosis of coronary artery disease. Significant lung uptake with stress Tc-99m N-NOET may also indicate the severity of disease.

Tc-99m Myocardial Perfusion SPECT Findings of Angina Patients Showing Normal Coronary Angiography

Background:Tc-99m myocardial perfusion imaging agents have recently found wide spread use as detecting agents of coronary diseases. Unfortunately, false positive results are not infrequent. Methods:We analyzed Tc-99m myocardial perfusion SPECT(Tc-SPECT findings in angina patients showing normal coronary angiography. Seventy patients who underwent myocardial SPECT wihin one month of coronary angiography which revealed no significant stenosis were studied. Results:Forty six(65.7% patients showed perfusion defects on Tc-SPECT. Eighteen were due to soft tissue attenuation, thirteen were due to technical problems such as low count rate, six were associated with intraventricular conduction abnormalities, four with coronary spasms, three with old infarctions, and one with slow coronary flow. Conclusion:Photon attenuation and inadequate count rates were the main causes of false positive results on myocardial SPECT imaging with Tc-99m agents. However, pathological conditions such as conduction disturbance, coronary spasm or slow coronary flow were also associated with positive SPECT findings in patients with normal coronary angiograms.

Simultaneous Tc-99m/Tl-201 imaging using energy-based estimation of the spatial distributions of contaminant photons

The advantages of simultaneous acquisition of Tc-99m and Tl-201 myocardial perfusion SPECT images can be fully realized only if the effects of the Tc-99m agent can be accurately removed from the Tl-201 image. We and others have previously reported simultaneous dual-isotope techniques for cardiac studies which make use of a third energy-window to estimate the Tc-99m scatter to be subtracted from the TI-201 window. We have recently demonstrated, however, using a Monte Carlo program which simulates all details of the photon transport, that lead X-rays produced in the collimator may also contribute significantly to contamination in the Tl-201 window. The spatial distribution of the Tc-99m scattered photons differs from that of the lead X-rays. Therefore, we modified our correction technique so that, at each projection angle, the contaminant image to be subtracted from the image in the Tl-201 window was estimated as a linear combination of a scatter-window (90-110 keV) image, blurred by a 2D Gaussian filter, and the Tc-99m photopeak image, blurred by a different Gaussian filter. For simulated data which included 'liver' activity and non-uniform 'lung' attenuation, the improved dual-window subtraction technique provided a more accurate estimate of the true TI-201 image, with less image noise, than did the single-window correction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

913-116 Quantitative Comparison of Planar and SPECT Normal Databases of Thallium-201, Sestamibi, Tetrofosmin and Furifosmin

For quantification of planar and SPECT myocardial perfusion imaging lower limits of normal (LLN) are generated for each specific radiotracer from normal subjects. It is unclear how LLN for TI-201 (TI), Tc-99m-Sestamibi (MB), Tc-99m-Tetrofosmin (TF) and Tc-99m-Furifosmin (FF) compare quantitatively Accordingly we performed quantitative comparison of exercise planar (P) and SPECT (SP) in normal subjects (&lt; 3% likelihood CAD) with TI (P:26, SP:26); MB (P:20, SP:28); TF (P:27, SP:42) and FF (P:12, SP:13). LLN (mean – 2sd) were generated using 36-points circumferential count profiles of P views and SP short axis slices, Comparisons were made by unpaired t-tests of each matched data point of 2 radiotracers, Summed t-values &gt; 2 (p &lt; 0,051 represent a measure for point-to-point significant difference between LLN curves, The higher the value the greater the difference. The figure shows t-values for comparison of various tracers for P and SP: LLN of various tracers are significantly different from each other and greater for P than for SP. On P imaging differences between TI and Tc-99m agents were primarily at base and anterior wall, whereas on SP no pattern existed. Differences in P imaging may be due to marked effect of interpolative background subtraction, whereas back projection and filtering produces smaller random SP differences. Thus, LLN of various agents are markedly different for P but less for SP. Radiotracer-specific normal databases should be used for quantification of P and SP myocardial perfusion imaging.

Technetium-Labeled Myocardial Perfusion Agents

Since its approval for clinical use in 1975, thallium-201 has been the mainstay for myocardial perfusion imaging to diagnose and manage patients with coronary artery disease. In 1992, 80% of 2.6 million myocardial perfusion imaging studies were done with thallium-201. Thallium-201 has important limitations, however, related to photon energy, half life, and availability. In December 1990, two Tc-99m-labeled agents (sestamibi and teboroxime) were approved for clinical use. There are ongoing clinical trials with other classes of Tc-99m agents. This article describes kinetics and imaging experience with Tc-99m-labeled perfusion agents.