Assessing time-of-flight signal-to-noise ratio gains within the myocardium and subsequent reductions in administered activity in cardiac PET studies

Armstrong, Ian; Tonge, Christine M.; Arumugam, Parthiban

doi:10.1007/s12350-017-0916-x

Cited by 12 publications

(13 citation statements)

References 18 publications

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“…Figure 1 b shows NEC rates taking the gain due to TOF into account as well, but this is valid only for the NEMA NEC measurement with a 20-cm phantom [ 9 , 10 ]. TOF benefits in a clinical cardiac scan are lower than what is shown here, but also in a clinical situation TOF will result in a considerable increase in signal to noise ratio compared with non-TOF reconstructions [ 11 ]. In this regard, TOF can improve image quality in cardiac perfusion imaging [ 12 ].…”

Section: Pet Technologymentioning

confidence: 99%

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

Sciagrà

Lubberink

Hyafil

et al. 2020

Eur J Nucl Med Mol Imaging

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The use of cardiac PET, and in particular of quantitative myocardial perfusion PET, has been growing during the last years, because scanners are becoming widely available and because several studies have convincingly demonstrated the advantages of this imaging approach. Therefore, there is a need of determining the procedural modalities for performing high-quality studies and obtaining from this demanding technique the most in terms of both measurement reliability and clinical data. Although the field is rapidly evolving, with progresses in hardware and software, and the near perspective of new tracers, the EANM Cardiovascular Committee found it reasonable and useful to expose in an updated text the state of the art of quantitative myocardial perfusion PET, in order to establish an effective use of this modality and to help implementing it on a wider basis. Together with the many steps necessary for the correct execution of quantitative measurements, the importance of a multiparametric approach and of a comprehensive and clinically useful report have been stressed.

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Section: Pet Technologymentioning

confidence: 99%

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

Sciagrà

Lubberink

Hyafil

et al. 2020

Eur J Nucl Med Mol Imaging

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“…In this issue of the Journal of Nuclear Cardiology, Armstrong et al investigate the SNR gain from TOF in cardiac viability imaging with FDG PET. 1 TOF works by evaluating the difference in the arrival time of the two coincidence gamma rays. Because the speed of light (c) is constant and finite, the difference in arrival times can be translated into a distance (x) from the center of the line-of-response (LOR) ( Figure 1A).…”

Section: See Related Article Pp 405-412mentioning

confidence: 99%

“…Armstrong et al 1 looked specifically at the SNR gain in cardiac viability imaging with FDG PET. They estimated the noise in each voxel of the myocardium using multiple replicate images generated by dividing the list-mode dataset into several short-time frames.…”

Section: See Related Article Pp 405-412mentioning

confidence: 99%

Does time-of-flight improve image quality in the heart?

Wells

deKemp

2019

Journal of Nuclear Cardiology

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See related article, pp. 405-412With the advent of fast Lutetium-based scintillation crystals, time-of-flight (TOF) positron emission tomography (PET) became a clinical reality. Although the crystals are still not fast enough to let us simply put photons back where they came from, incorporation of TOF information into the reconstruction of PET images has led to a substantial gain in signal-to-noise ratio (SNR), particularly for larger patients. The benefits of TOF have been shown with numerous oncology studies but there has been, to date, little evidence regarding TOF in cardiac studies. In this issue of the Journal of Nuclear Cardiology, Armstrong et al. investigate the SNR gain from TOF in cardiac viability imaging with FDG PET. 1 TOF works by evaluating the difference in the arrival time of the two coincidence gamma rays. Because the speed of light (c) is constant and finite, the difference in arrival times can be translated into a distance (x) from the center of the line-of-response (LOR) ( Figure 1A). With this information, the location of the annihilation event can be determined by the difference in arrival times of the two annihilation photons (t i ). The distance a photon travels (d i ) in time t i is given by d i = t i 9 c. Therefore,and the uncertainty in the position x (r x ) are given bywhere r Dt is the timing resolution of the scanner.If the timing resolution was perfect, we would not even need to do a reconstruction because we could just put each detected count back at its point of origin. However, the timing resolution is not perfect. With BGO crystals, the typical timing resolution is on the order of 5 ns, which translates into a spatial resolution of about 75 cm. In this case, TOF does not add much information because the position uncertainty is larger than the bore size of the scanner. However, with the Lutetium-based scintillators, timing resolution is on the order of 500 ps and so the corresponding uncertainty in the position of the annihilation event is only 7.5 cm. Now, when we go to reconstruct the image, the probability of an event's location is not spread evenly over the entire LOR, but it is instead confined to a small portion of the line-a Gaussian probability with a full-width at half-maximum equal to the spatial positioning uncertainty ( Figure 1B). One of the benefits of TOF is that reducing the uncertainty in where each event is located results in a reduction in the propagation of noise along each LOR. The influence of each count is restricted spatially and so the noise from distant objects in the field of view (FOV) is no longer present. Lower noise means a higher SNR.The increase in SNR from TOF PET has been recognized for some time. In 1983, Budinger 2 described the relationship and showed that the gain in SNR should be approximately equal towhere µD is the diameter of a uniform cylinder. The use of a non-linear iterative reconstruction algorithm instead of filtered backprojection, as well as other factors, can alter the SNR 3 and so the gain in SNR from TOF is not quite as hig...

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“…2,3 However, translating SNR gains to the myocardium is not straightforward due to the highly nonuniform shape and density of the patient and also the challenge of defining an appropriate region in which to measure voxel noise. 4,5 The ubiquitous use of iterative reconstruction adds further complication when assessing SNR gains from TOF as SNR is dependent on the number of updates to the estimated image-usually defined as the product of the number of iterations and subsets. TOF has been shown to accelerate convergence, particularly when measuring contrast recovery of hot spheres in a warm background activity.…”

Section: See Related Article Pp 1521-1545mentioning

confidence: 99%

“…11 Similar findings were also demonstrated when looking at SNR gains from TOF in the myocardium. 4 This may be because patients carry weight in different places. Male patients with high BMI are likely to have greater amounts of abdominal tissue, whereas female patients are more likely to have greater amounts of breast tissue.…”

Section: See Related Article Pp 1521-1545mentioning

confidence: 99%

Assessing time-of-flight signal-to-noise ratio gains within the myocardium and subsequent reductions in administered activity in cardiac PET studies

Abstract: A method to quantify SNR gains from TOF within the myocardium has been developed and evaluated. SNR gains within the myocardium are comparable to those observed by established methods. This allows guidance for protocol optimization for TOF systems in cardiac PET.

Cited by 12 publications

References 18 publications

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

EANM procedural guidelines for PET/CT quantitative myocardial perfusion imaging

Does time-of-flight improve image quality in the heart?

Understanding the impact of advanced PET reconstruction in cardiac PET: The devil is in the details

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