Phantom evaluation of simultaneous thallium-201/technetium-99m aquisition in single-photon emission tomography

Cao, ZX; Chen, Charles C.; Maunoury, C.; Holder, Lawrence E.; Abraham, Titus; Tehan, Ann M.

doi:10.1007/bf01254477

Cited by 15 publications

(16 citation statements)

References 7 publications

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“…The photons emitted during 201 Tl disintegration are mostly x-rays having a relatively broad energy spectrum. Moreover, the administration of a low dose of 201 Tl results in low counting rates and poor statistics compared with those of the other radioisotopes used in nuclear medicine (14).…”

Section: Discussionmentioning

confidence: 99%

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Optimized Energy Window Configuration for 201Tl Imaging

Kalantari¹,

Rajabi²,

Yaghoobi³

2008

Journal of Nuclear Medicine Technology

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A poor signal-to-noise ratio attributable to a low injected dose of thallium and the presence of scattered photons are the major impediments in the use of thallium as an imaging agent. Thallium decays in a complicated way and emits photons in a wide range of energies (68-82 keV). To increase the ratios of primary photons to scatter photons (primary-to-scatter ratios) and possibly increase system sensitivity, a new energy window for thallium was investigated. Methods: The NCAT phantom was used to simulate the distribution of activity and the attenuation coefficient in a typical patient torso. The phantom was imaged with a SPECT simulator in different energy window configurations. The energy spectra for primary photons and scatter photons were generated, and the most suitable energy windows were investigated. To evaluate the results of the simulation study, a physical phantom was imaged in different energy windows with a SPECT system. The images of the physical phantom were analyzed for the best-quality image and the corresponding window setting. To evaluate the windows determined in the simulation and phantom studies, SPECT images of 7 patients who had angiographically confirmed myocardial defects were acquired in different energy windows. The images were quantitatively compared on the basis of the calculated contrast, scatter-to-noise ratio, and sensitivity. The images were also qualitatively evaluated independently by 4 nuclear medicine specialists. Results: The simulation study showed that the conventional window setting (68 6 10% keV) is not the most suitable window configuration for 201 Tl imaging and that the optimum energy window is 77 6 15% keV. The images acquired in the latter window configuration yielded higher primary-to-scatter ratios, higher sensitivity (total counts), and better contrast than the images acquired in the conventional window configuration. The phantom study confirmed the results of the simulation study. In the clinical study, the images acquired in the suggested window showed a considerable increase in myocardium-to-defect contrast (1.541 6 0.368) and myocardium-to-cavity contrast (1.171 6 0.099) than those acquired in the conventional window configuration. Conclusion: The energy window configuration of 77 6 15% keV yields higher-quality images than the conventional window configuration.

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Section: Discussionmentioning

confidence: 99%

“…There are many different protocols for adjusting the energy windows in 201 Tl imaging (12)(13)(14)(15)(16)(17)(18), although commonly thallium images are acquired in 2 energy windows (11). The first energy window is set at the x-ray photopeak (68 6 10% or 68 6 15% keV), and the second window is set at the g-6 photopeak (167 6 20% keV).…”

mentioning

confidence: 99%

Optimized Energy Window Configuration for 201Tl Imaging

Kalantari¹,

Rajabi²,

Yaghoobi³

2008

Journal of Nuclear Medicine Technology

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“…For example, 99m Tc photons emitted at 140 keV can be detected in the 201 Tl photopeak, centered around 72 keV, owing to energy loss in Compton scatter interactions or via the emission of lead X-rays from the collimator [4]. This down-scatter can lead to gross overestimation in activity and loss of contrast in small lesions [5,6,7,8]. For example, an irreversible defect (indicating non-viable tissue) in separate 99m Tc/ 201 Tl SPET can be interpreted as a reversible defect (indicating viable tissue) in DI-SPET, which may lead to needless angioplasty or bypass surgery, if down-scatter is not corrected for.…”

Section: Introductionmentioning

confidence: 99%

“…For example, an irreversible defect (indicating non-viable tissue) in separate 99m Tc/ 201 Tl SPET can be interpreted as a reversible defect (indicating viable tissue) in DI-SPET, which may lead to needless angioplasty or bypass surgery, if down-scatter is not corrected for. In general, 99m Tc/ 201 Tl DI-SPET is often regarded as unsuitable for clinical use without adequate correction for the effects of down-scatter [2,5,8,9]. Several methods have been proposed to correct for down-scatter [10,11,12,13].…”

Section: Introductionmentioning

confidence: 99%

Simultaneous 99mTc/201Tl dual-isotope SPET with Monte Carlo-based down-scatter correction

et al. 2002

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In simultaneous technetium-99m/thallium-201 dual-isotope (DI) single-photon emission tomography (SPET), down-scatter of (99m)Tc photons contaminates the (201)Tl image, which leads to a decrease in lesion contrast and loss of quantitative accuracy. Correction for down-scatter can be achieved by first reconstructing the (99m)Tc activity distribution. Subsequently, the (99m)Tc down-scatter in the (201)Tl photopeak window is simulated and used for correction during iterative reconstruction of the (201)Tl image. In this work, the down-scatter projections are calculated using a dedicated Monte Carlo simulator which is able to efficiently model the detection of lead X-rays from the collimator. An anthropomorphic torso phantom with a cardiac insert with and without cold lesions was used for evaluation of the proposed method. Excellent agreement in lesion contrast and quantitative accuracy was found between the down-scatter corrected DI-SPET (201)Tl image and the virgin (i.e. separately acquired) (201)Tl image, in particular when the effects of lead X-rays were included. Compensation for the noise added by down-scatter to the (201)Tl image can be achieved by using a 15% lower dose of (99m)Tc, a 15% increase in scan time and a 12% increase in (201)Tl dose. In conclusion, the Monte Carlo-based down-scatter correction recovers lesion contrast and quantitative accuracy in DI-SPET (201)Tl images almost perfectly. In addition, degradations due to the added noise of down-scatter in simultaneous DI-SPET can be prevented by slight adaptations to the data acquisition protocol.

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“…While these methods lead to improvements in quantitation and contrast in the Tl image, they each have disadvantages similar to those associated with single-isotope scatter subtraction methods: each requires ad hoc determination of parameters such as scaling factors or blurring functions, the cross-talk estimate may not be accurate for all imaging situations, and the subtraction (or deconvolution) step is accompanied by a large increase in statistical noise. In a phantom evaluation by Cao et al (1996), subtraction-based crosstalk compensation methods were found to overestimate defect size and resulted in increased heterogeneity in the myocardial wall in some situations.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous technetium-99m/thallium-201 SPECT imaging with model-based compensation for cross-contaminating effects

1999

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Simultaneous acquisition of dual-isotope SPECT data offers a number of advantages over separately acquired data; however, simultaneous acquisition can result in cross-contamination between isotopes. In this work we propose and evaluate two frameworks for iterative model-based compensation of cross-contamination in dual-isotope SPECT. The methods were applied to cardiac imaging with Technetium-99m-sestamibi and Thallium-201, and they were compared to a subtraction-based compensation method using a cross-talk estimate obtained from an auxiliary energy window. Monte Carlo simulations were performed to carefully study aspects of bias and noise for the methods, and a torso phantom with cardiac insert was used to evaluate the performance of the methods for experimentally acquired data. The cross-talk compensation methods substantially improved lesion contrast and significantly reduced quantitative errors for simultaneously acquired data. Thallium image normalized mean square error (NMSE) was reduced from 0.522 without cross-talk compensation to as low as 0.052 with model-based cross-talk compensation. This is compared to a NMSE of 0.091 for the subtraction-based compensation method. The application of a preliminary model for crosstalk arising from lead fluorescence x-rays and collimator scatter gave promising results, and the future development of a more accurate model for collimator interactions would likely benefit simultaneous Tc/Tl imaging. Model-based compensation methods provide feasible cross-talk compensation in clinically acceptable times, and they may ultimately make simultaneous dualisotope protocols an effective alternative for many imaging procedures.

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Phantom evaluation of simultaneous thallium-201/technetium-99m aquisition in single-photon emission tomography

Cited by 15 publications

References 7 publications

Optimized Energy Window Configuration for 201Tl Imaging

Optimized Energy Window Configuration for 201Tl Imaging

Simultaneous 99mTc/201Tl dual-isotope SPET with Monte Carlo-based down-scatter correction

Simultaneous technetium-99m/thallium-201 SPECT imaging with model-based compensation for cross-contaminating effects

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