Improved diagnostic accuracy of thallium-201 myocardial perfusion single-photon emission computed tomography with CT attenuation correction

BACKGROUND

The benefits of attenuation correction (AC) in technetium-99m myocardial perfusion imaging (MPI) have been well established. However, the value of thallium (Tl-201) AC and routine computed tomography AC (CTAC) were less well established. The aims of this study were to evaluate the diagnostic performance of thallium (Tl-201) MPI with additional CTAC and to determine which participants would benefit most.

METHODS AND RESULTS

A total of 108 consecutive patients who underwent Tl-201 MPI and received coronary angiography within 3 months were enrolled. Diagnostic performance was determined by sensitivity, specificity, and receiver operating characteristic curve analysis. Subgroup analyses were performed using gender and obesity. CTAC improved the area under the curve (0.84 vs. 0.77, P = 0.037 at patient level), primarily due to a significant improvement in specificity (0.78 vs. 0.57, P = 0.013) and no significant difference in sensitivity (0.79 vs. 0.82, P = 0.75). In subgroup analysis, CTAC was most helpful in obese subjects, men, and especially right coronary artery lesions.

CONCLUSIONS

CTAC significantly improved diagnostic performance primarily by increasing the specificity, and the improvements were significantly greater in obese patients and male patients. These findings suggest that CTAC should be applied to Tl-201 MPI as routine clinical practice.

Thallium stable isotope fractionation in white mustard: Implications for metal transfers and incorporation in plants

We studied thallium (Tl) isotope fractionation in white mustard grown hydroponically at different Tl doses. Thallium isotope signatures in plants indicated preferential incorporation of the light ²⁰³Tl isotope during Tl uptake from the nutrient solution. Negative isotope fractionation was even more pronounced in dependence on how much the available Tl pool decreased. This finding corresponds to the concept of isotope overprinting related to a high contamination level in the growing media (solution or soil). Regarding Tl translocation in plants, we observed a large Tl isotope shift with an enrichment in the heavy ²⁰⁵Tl isotope in the shoots relative to the roots in treatments with low/moderate solution Tl concentrations (0.01/0.05 mg Tl/L), with the corresponding α^205/203Tl fractionation factors of ˜1.007 and 1.003, respectively. This finding is probably a consequence of specific (plant) reactions of Tl replacing K in its cycle. The formation of the S-coordinated Tl(I) complexes, potentially affecting both Tl accumulation and Tl isotope fractionation in plants, however, was not proven in our plants, since we did not have indication for that on the basis of X-ray absorption spectroscopy, suggesting that Tl was mainly present as free/hydrated Tl⁺ ion or chemically bound to O-containing functional groups.

Diagnostic value of ultrasonography and TI-201/Tc-99m dual scintigraphy in differentiating between benign and malignant thyroid nodules

PURPOSE

To evaluate the performance of ultrasonography (US) and TI-201/Tc-99m dual (Tl/Tc) scintigraphy in differentiating between benign and malignant thyroid nodules.

METHODS

Eighty-six patients diagnosed to have a thyroid tumor on postoperative histopathologic examination between June 2009 and February 2017 were included in this retrospective study. A radiologist reviewed the US and Tl/Tc scintigraphy reports along with all available clinical and histopathologic information. On Tl/Tc scintigraphy, a nodule in which uptake was higher in the delayed phase than in the surrounding parenchyma was defined as a delayed accumulation pattern and a nodule in which uptake was higher in the delayed phase than in the early phase was defined as a persistent pattern. The Tl/Tc scintigraphy images were evaluated in a blinded manner to assess reproducibility. A statistical analysis was performed to identify features associated with malignancy. Interobserver variability was calculated using the κ statistic.

RESULTS

US had higher sensitivity (81.2%), specificity (88.2%), and positive (96.6%) and negative (53.6%) predictive values than Tl/Tc scintigraphy. An ill-defined margin and microcalcification were independent predictors of a malignant thyroid nodule on multivariate logistic regression (P = 0.003 and P = 0.014, respectively). The persistent pattern had high specificity (85.7%) equivalent to that of US but had lower sensitivity (34.7%). The κ values for the delayed accumulation and persistent patterns were 0.66-0.78 and 0.32-0.50, respectively.

CONCLUSIONS

An ill-defined margin and microcalcification on US were independent predictors of a malignant thyroid nodule. A persistent pattern seen on Tl/Tc scintigraphy could contribute to the differential diagnosis.

An Exploratory Study of Washout Rate Analysis for Thallium-201 Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging Using Cadmium Zinc Telluride Detectors

The aim of this study was to assess the washout rate (WOR) for thallium-201-chloride single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using cadmium zinc telluride detectors for SPECT (CZT SPECT) versus conventional Anger-type SPECT (conventional SPECT). A total of 52 Japanese patients were examined using CZT SPECT and conventional SPECT, and the global WORs were compared. Additionally, the MPI WORs were compared for patients with a normal MPI versus those in whom MPI reflected the patients’ multivessel disease (MVD) MPI. Washout rates were similar when approximated by CZT SPECT versus conventional SPECT 12.59 ± 2.26%/h vs 12.57 ± 2.27%/h (P = .997), respectively. The WOR values for CZT SPECT versus conventional SPECT were 13.42%/h (1.53%/h) vs 13.93%/h (1.24%/h) (P = .337), respectively, for 7 normal MPI patients, and 10.64 ± 2.20%/h vs 10.84 ± 2.26%/h (P = .848), respectively, for 7 MVD-MPI patients. The WOR values for normal MPI versus MVD-MPI patients for CZT SPECT were 13.42 ± 1.53%/h vs 10.64 ± 2.20%/h (P = .025), respectively. Thallium-201-chloride WOR values obtained with high-efficiency CZT SPECT, which enabled significantly reduced imaging times and use of a low-dose protocol, were similar to those obtained with conventional SPECT.

Influence of acquisition orbit on phase analysis of gated single photon emission computed tomography myocardial perfusion imaging for assessment of left ventricular mechanical dyssynchrony

OBJECTIVE

The association between left ventricular (LV) dyssynchrony parameters, given by phase analysis of gated single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI), and acquisition orbits is unclear. The aim of this study was to assess the dependence of LV dyssynchrony parameters on acquisition orbits.

METHODS

Ninety-nine patients who underwent ²⁰¹Tl-gated SPECT MPI were categorized into minor hypoperfusion or major hypoperfusion groups. Forty-four patients who underwent ^99mTc-tetrofosmin-gated SPECT MPI were categorized into minor hypoperfusion or major hypoperfusion groups. The major hypoperfusion group with ²⁰¹Tl was divided into inferior or non-inferior wall hypoperfusion subgroups, and anteroseptal or non-anteroseptal wall hypoperfusion subgroups. Gated SPECT MPI data over a 360° acquisition orbit (360° images) and a 180° acquisition orbit (180° images) were reconstructed, and histogram bandwidth (HBW) and phase standard deviation (PSD) were compared.

RESULTS

Between 360° and 180° images with ²⁰¹Tl, there were significant differences in HBW and PSD both globally (HBW 34.8 ± 16.6 vs. 29.1 ± 10.2; PSD 8.8 ± 4.9 vs. 7.0 ± 2.3, p < 0.05 for both) and in the inferior wall (HBW 29.5 ± 15.5 vs. 23.3 ± 9.0; PSD 7.6 ± 4.6 vs. 5.6 ± 2.4, p < 0.001 for both) in the major hypoperfusion group, and also in the inferior wall in all subgroups of the major hypoperfusion group. In contrast, no segment had any significant differences in HBW or PSD between 360° and 180° images with ^99mTc.

CONCLUSION

Differences in acquisition orbit had a significant influence on HBW and PSD with ²⁰¹Tl-gated SPECT MPI in the inferior wall in patients with major hypoperfusion myocardium.

Thallium-201 is comparable to technetium-99m-sestamibi for estimating cardiac function in patients with abnormal myocardial perfusion imaging

We analyzed the left-ventricular functional data obtained by cardiac-gated single-photon emission computed tomography myocardial perfusion imaging (MPI) with thallium-201 (Tl-201) and technetium-99m-sestamibi (MIBI) protocols in different groups of patients, and compared the data between Tl-201 and MIBI. Two hundred and seventy-two patients undergoing dipyridamole stress/redistribution Tl-201 MPI and 563 patients undergoing 1-day rest/dipyridamole stress MIBI MPI were included. Higher mean stress ejection fraction (EF), rest EF, and change in EF (ΔEF) were noticed in the normal MPI groups by both Tl-201 and MIBI protocols. Higher mean EF was observed in the females with normal MPI results despite their higher mean age. Comparisons between the Tl-201 and MIBI groups suggested a significant difference in all functional parameters, except for the rest end diastolic volume/end systolic volume and ΔEF between groups with negative MPI results. For the positive MPI groups, there was no significant difference in all parameters, except for the change in end diastolic volume and change in end systolic volume after stress between both protocols. The Tl-201 provides comparable left-ventricular functional data to MIBI cardiac-gated single-photon emission computed tomography in patients with positive MPI results, and may therefore be undertaken routinely for incremental functional information that is especially valuable to this patient group.

Prediction of revascularization after myocardial perfusion SPECT by machine learning in a large population

OBJECTIVE

We aimed to investigate if early revascularization in patients with suspected coronary artery disease can be effectively predicted by integrating clinical data and quantitative image features derived from perfusion SPECT (MPS) by machine learning (ML) approach.

METHODS

713 rest (201)Thallium/stress (99m)Technetium MPS studies with correlating invasive angiography with 372 revascularization events (275 PCI/97 CABG) within 90 days after MPS (91% within 30 days) were considered. Transient ischemic dilation, stress combined supine/prone total perfusion deficit (TPD), supine rest and stress TPD, exercise ejection fraction, and end-systolic volume, along with clinical parameters including patient gender, history of hypertension and diabetes mellitus, ST-depression on baseline ECG, ECG and clinical response during stress, and post-ECG probability by boosted ensemble ML algorithm (LogitBoost) to predict revascularization events. These features were selected using an automated feature selection algorithm from all available clinical and quantitative data (33 parameters). Tenfold cross-validation was utilized to train and test the prediction model. The prediction of revascularization by ML algorithm was compared to standalone measures of perfusion and visual analysis by two experienced readers utilizing all imaging, quantitative, and clinical data.

RESULTS

The sensitivity of machine learning (ML) (73.6% ± 4.3%) for prediction of revascularization was similar to one reader (73.9% ± 4.6%) and standalone measures of perfusion (75.5% ± 4.5%). The specificity of ML (74.7% ± 4.2%) was also better than both expert readers (67.2% ± 4.9% and 66.0% ± 5.0%, P < .05), but was similar to ischemic TPD (68.3% ± 4.9%, P < .05). The receiver operator characteristics areas under curve for ML (0.81 ± 0.02) was similar to reader 1 (0.81 ± 0.02) but superior to reader 2 (0.72 ± 0.02, P < .01) and standalone measure of perfusion (0.77 ± 0.02, P < .01).

CONCLUSION

ML approach is comparable or better than experienced readers in prediction of the early revascularization after MPS, and is significantly better than standalone measures of perfusion derived from MPS.

Stress thallium-201/rest technetium-99m sequential dual-isotope high-speed myocardial perfusion imaging validation versus invasive coronary angiography

BACKGROUND

Recent advances in nuclear myocardial perfusion imaging (MPI) have made it possible to develop a dual-isotope protocol for high-speed acquisition with image quality and radiation delivery comparable to that obtained with conventional single isotope protocols. So far, no study has compared dual-isotope high-speed MPI to invasive coronary angiography (ICA) in a large cohort using a Cadmium-zinc-telluride SPECT system.

METHODS

Over a 1-year period (May 2011 to April 2012), 1366 patients underwent dual-isotope high-speed MPI. Patients with ICA within 3 months after dual-isotope high-speed MPI were included together with patients with a low likelihood of coronary artery disease (CAD) in order to assess normalcy rate. Global summed stress score (SSS) and summed rest score (SRS) were calculated, and ICA results were analyzed independently. The main end point was a patient-based assessment of the diagnostic performance of dual-isotope high-speed MPI in detecting or ruling out significant CAD (>70% reduction in lumen diameter).

RESULTS

Inclusion criteria were fulfilled for 214 patients (143 men; age 60 ± 14 years; ICA, n = 104; low likelihood for CAD, n = 110). An exercise stress test was performed in 62% of patients and a pharmacological stress test was performed with either dipyridamole (32%) or dobutamine (6%). Average examination duration was 22.4 ± 4.5 minutes. Mean SSS, SRS, and SDS were 8.0 ± 4.9, 3.1 ± 4.3, and 5.0 ± 3.2, respectively. Prevalence of angiographic CAD was 75%. ICA detected stenosis in the left main trunk, left anterior descending artery, left circumflex artery, and right coronary artery in 4, 33, 31, and 42 patients, respectively. Sensitivity of dual-isotope high-speed MPI was 94%, normalcy rate was 92%, and accuracy was 83% for detecting CAD.

CONCLUSION

Dual-isotope high-speed MPI is reliable at detecting or ruling out CAD. NCT01785589.

Does perfusion pattern influence stress-induced changes in left ventricular mechanical dyssynchrony on thallium-201-gated SPECT myocardial perfusion imaging?

BACKGROUND

The relationship between perfusion pattern and stress-induced changes in left ventricular mechanical dyssynchrony (LVMD) on stress-rest thallium-201-gated SPECT myocardial perfusion imaging (Tl-201 SPECT MPI) is not clear. The aim of the study is to assess the relation of perfusion pattern with stress-induced changes in LVMD on Tl-201 MPI.

METHODS

Data of 194 patients who underwent exercise-rest Tl-201 MPI between January to December 2012 at our institute was retrospectively evaluated. Institute Ethical committee approval was obtained. Fifty patients who underwent Tl-201 MPI for suspected CAD and had normal LV perfusion and function on MPI were taken as normal group. Patients with perfusion abnormalities (n = 144) were divided into three groups: ischemia (n = 66), infarct (n = 32), and mixed group (n = 46; ischemia and infarct both). Summed stress score, summed rest score, summed difference score (SDS), and LV ejection fraction (EF) were evaluated. Two LVMD parameters, phase standard deviation (PSD) and phase histogram bandwidth (PHB), were assessed in post-stress and rest MPI images. ΔPSD (post-stress PSD - rest PSD) and ΔPHB (post-stress PHB - rest PHB) were calculated to measure stress-induced changes in LVMD.

RESULTS

In all the groups, mean post-stress LVMD parameters were lower as compared to LVMD parameters at rest. Post-stress PSD was significantly lower than rest PSD in all groups. Similar trend was noted with PHB values also, but it was statistically significant in the normal and ischemia group only. Post-stress worsening of at least one of the LVMD parameters was noted in 28 patients and all these patients had perfusion abnormalities. But on subgroup analysis, no difference was found in proportion of patients showing post-stress worsening of LVMD between ischemia (13.6%), infarct (25%), and mixed (23.6%) groups. No significant correlation was found between ΔPSD/ΔPHB and ΔLVEF/SDS in any group.

CONCLUSION

LV mechanical dyssynchrony parameters are smaller in post-exercise stress as compared to rest on Tl-201 MPI, regardless of perfusion pattern. Stress-induced worsening of LV dyssynchrony was observed only in patients with perfusion abnormalities, but this is not related to the type of perfusion abnormality.

²⁰¹Tl⁺-labelled Prussian blue nanoparticles as contrast agents for SPECT scintigraphy

Prussian blue (PB) and its analogues on the nanometric scale are exciting nano-objects that combine the advantages of molecular-based materials and nanochemistry. Herein, we demonstrate that ultra-small PB nanoparticles of 2-3 nm can be easily labelled with radioactive (201)Tl(+) to obtain new nanoprobes as radiotracers for 201-thallium-based imaging.

Output of radiopharmaceutical nuclides of known injected doses from a municipal sewage treatment system

The concentrations of (99m)Tc, (123)I, (67)Ga, and (201)Tl of the discharge water and the sewage sludge from Kurume Central Sewage Treatment Plant were determined once a week for 2 mo. The radiopharmaceutical doses injected into the patients for all of four hospitals that use nuclear medicines in the service area of the plant were also surveyed. Approximately 1.5% of the (99m)Tc, 1.5% of the (123)I, 4.3% of the (67)Ga, and 0.41% of the (201)Tl of the injected doses were detected in the discharged water from the plant. The behavior of these radionuclides in the sewage treatment system was analyzed using a compartment model. The analyses suggest that the average residence times in storage tanks and drainage pipes before entering the plant were 9.5 h for (99m)Tc, 81 h for (123)I, 120 h for (67)Ga, and 480 h for (201)Tl.

Effect of denture base surface pretreatment on microleakage of a silicone-based resilient liner

STATEMENT OF PROBLEM

Microleakage between resilient liner and denture base resins is a significant clinical problem, often responsible for debonding of the resilient liner from the denture base resin.

PURPOSE

This study investigated the effect of 2 surface treatments, airborne-particle abrasion (APA) and wetting with methyl methacrylate monomer (MMA), on microleakage between a silicone-based resilient liner and denture base resin using a gamma camera imaging technique.

MATERIAL AND METHODS

Thirty-three specimens, each having 2 plates measuring 40 x 40 x 2 mm, were prepared by packing and processing an acrylic denture base resin (QC-20) into square plates following manufacturer's instructions. Specimens were divided into 3 groups (n=11) as APA-, MMA-, and control-treatment groups. For the APA group, the inner surfaces of both plates were airborne-particle abraded with 250-microm Al 2 O 3 particles and, for the MMA group, surfaces were treated with monomer (QC-20). Control specimens were not surface treated. Following application of an adhesive (Ufi Gel P-specific), a silicone lining material (Ufi Gel P) was prepared and applied to the inner surfaces of all 33 specimens. Eleven size-matched polymethyl methacrylate (PMMA) specimen blocks (40 x 40 x 6 mm) were prepared to calculate the level of residual radioactivity for the denture base itself, the entire outer surface count (OSC). All specimens and PMMA blocks were immersed in a radioactive solution (thallium-201 chloride) for 24 hours. Specimen activities (gamma-ray cts/sec, representing thallium-201 concentration) were then measured using a high-resolution gamma camera. The amount of OSC-subtracted total specimen counts was a direct indicator of the quantity of inward diffusing tracer. The subtracted values were analyzed using a 1-way analysis of variance (ANOVA) and Bonferroni multiple comparison tests (alpha=.05).

RESULTS

OSC levels averaged 754 +/- 110 gamma-ray cts/sec. OSC-subtracted APA, control, and MMA values were 5,546 +/- 1,534, 3,392 +/- 738, and 1,405 +/- 392 gamma-ray cts/sec, respectively. All 3 groups were significantly different ( P <.05) from each other. Surface wetting with MMA showed the lowest microleakage values among all specimen groups.

CONCLUSION

In terms of microleakage, surface treatment with MMA monomer preceding the adhesive application demonstrated lower values than adhesive application alone. APA pretreatment resulted in 4 times the microleakage found in MMA-treated specimens, and 1.5 times the microleakage of the untreated control. None of the surface pretreatments completely prevented microleakage. Microleakage between the silicone-based resilient liner and denture base resin can be quantitatively determined using the gamma camera imaging technique.

Measurements of nuclear data parameters of 201Tl by gamma-ray spectrometry

201Tl is frequently used in radiopharmaceutical applications, and therefore the gamma-ray emission probabilities and half-life have been re-determined by means of gamma-ray spectroscopy. While the activity was calibrated using the sum-peak coincidence method, the half-life was obtained by the reference source method based on simultaneous counting of a reference source and the sample. Both the measurement techniques and assignment of uncertainties are presented and discussed, and the resulting data are shown to be in good agreement with previously published studies.

Oxidation of thallium by freshwater plankton communities

Thallium is a toxic metal that is of emerlI(I) or Tl(III), and its oxidation state affects its complexation and subsequent bioavailability and toxicity. We conducted lab and field incubations with 204Tl(I) and natural plankton assemblages to study the occurrence and mechanism of Tl oxidation. We observed that Tl(III) comprised 74% of total dissolved Tl after a 60 h incubation in surface waters from Lake Ontario, revealing a maximum specific oxidation rate of 0.014 h(-1). No Tl(I) oxidation was observed in sterile-filtered control treatments, indicating that solar radiation alone does not oxidize Tl(I) to Tl(III). Additional incubations with pond water revealed that Tl(I) oxidation is mediated by microbial activity and is not related to the presence of abiotic particles or phytoplankton or protozoa. We also identified a minor fraction (5-13%) of nonion-exchangeable (Chelex-100 resin; pH 1.5) Tl that may represent dimethylthallium or complexed thallium. This study demonstrates that planktonic bacteria are responsible for oxidizing the thermodynamically stable Tl(I) to the more abundant Tl(III).

Preparation of "high specific activity" radiochemical forms of vanadium, manganese and thallium for metallo-toxicological studies

In this paper are presented the production methods for very "high specific activity" radionuclides (HSA-RN) of vanadium, manganese and thallium which have been developed in our laboratories for labelling different chemical forms of these elements present in the echo-systems in ultra-trace amounts, for metallo-toxicological and bio-kinetic studies. Use was made of both cyclotron and thermal nuclear reactor. If the nuclear reaction product has atomic number different from irradiated target, it is possible separating the radioactive nuclide from irradiated target, without addition of isotopic carrier. This kind of radionuclide is named No Carrier Added, NCA, and his specific activity, As is very high and can reach values close to the theoretical Carrier Free one, CF. The experimental determination of specific activity, chemical and radiochemical purities is mandatory for all these kinds of applications.