Evaluation of digital PET/CT system for myocardial perfusion imaging

Myocardial perfusion imaging (MPI) with Positron Emission Tomography (PET) allows quantitative measurements of absolute myocardial blood flow (MBF). PET system count-rate capabilities, reconstruction techniques, and other technical factors may influence MBF quantification reproducibility and accuracy. In this thesis the aims were to evaluate the effect of different reconstruction parameters on [15O]H2O MPI using a flow phantom and clinical retrospective data from patients who had undergone [15O]H2O MPI for suspected obstructive coronary artery disease. Also, the digital and analog PET system count-rate capabilities were assessed in high count-rate studies. Finally, the aim was to establish the contribution of technical factors on quantitative reproducibility and accuracy on two digital PET systems. The different reconstruction parameters resulted in a 7 % relative error with the image-derived flow values compared to the reference flow values in phantom studies. Similar differences were measured in MBF values in patients. Also, different reconstruction algorithms resulted in similar classification of myocardial ischemia in 99 % of the subjects. The digital PET resulted in 12.8 Mcps total prompts and 0.47 Mcps trues, and the analog PET in 6.85 Mcps total prompts and 1.15 Mcps trues with the highest injected activities. The modelled flow values were reproducible on digital PET systems but future studies need to be conducted to develop a standardized and repeatable bolus injection protocol. The results of these studies showed that the digital PET system can be reliably used in MPI in terms of system count-rate capabilities and novel reconstruction techniques with small contribution from technical factors. The findings offer a basis for assessing reproducibility in MPI in multi-center studies

LYSO-SiPM-ilmaisintekniikkaan perustuvan digitaalisen PET-kameran suorituskyvyn arviointi H215O-torsofantomilla

Positroniemissiotomografia (PET) on kajoamaton lääketieteellinen kuvantamismenetelmä, joka perustuu radioaktiivisen merkkiaineen kertymiseen kehoon. Sydämen verenvirtauksen kuvantamisessa on PET-kuvan pohjalta mahdollista määrittää sydämen verenvirtauksen kvantitatiiviset arvot. Sydänperfuusiokuvauksessa PET-TT-kameran suorituskyvyn tulee säilyä luotettavalla tasolla suurillakin aktiivisuuksilla. Tällöin PET-kuvista määritettävät sydämen verenvirtauksen arvot voidaan laskea luotettavasti. Suurilla aktiivisuuksilla ilmaisimen kuollut aika sekä fotonien sirontaosuuden määrä saattavat lisääntyä, mikä vaikuttaa heikentävästi laitteiston suorituskykyyn. Tässä tutkimuksessa on tutkittu uuden digitaalisen LYSO-SiPM-ilmaisinta käyttävän PET-TT-laitteiston suorituskykyä suurilla aktiivisuuksilla hyödyntäen antropomorfista torsofantomia, jonka sydäntä mallintavaan keittosuolapulloon injisoitiin H215O-merkkiainetta yli 1500 MBq. Suorituskyvyn tarkastelemiseksi kerättiin fantomimittauksista koinsidenssihavaintojen määrä, kuolleen ajan kertoimet sekä sirontaosuuden kertoimet aktiivisuusalueen yli. Lisäksi tarkasteltiin aktiivisuusalueelta systeemin teoreettisten koinsidenssihavaintojen sekä menetettyjen havaintojen määrää. Työssä kerättiin myös Turun PET-keskuksen sydänperfuusiopotilaiden koinsidenssihavaintojen määrät, kuolleen ajan kertoimet sekä sirontaosuuden kertoimet ja verrattiin niiden sijoittumista fantomeiden käyrille. Laitteiston suorituskyvyn sekä potilaiden parametrien perusteella arvioitiin, oliko nykyinen aktiivisuuden injektioraja nostettavissa sydänperfuusiokuvauksissa. Laitteiston suorituskyvyn havaittiin pysyvän lineaarisena 630 MBq asti, kunnes kuolleen ajan kertoimen arvo ylitti 1,9 ja koinsidenssihavaintojen määrä säilyi vakiona 12,8 Mcps. Sirontaosuuden kertoimen maksimiarvo saavutettiin 35 %, mutta 630 MBq ylittävillä aktiivisuuksilla havaittiin sirontaosuuden aliarvioituvan. Potilaiden kuolleen ajan kertoimen ja koinsidenssihavaintojen määrän havaittiin sijoittuvan fantomeiden käyrille kohtaan, jossa laitteiston suorituskyky säilyi lineaarisena. Täten potilaiden sydänperfuusiotutkimusten injektioannosta arvioitiin voitavan nostaa 700 MBq tasolle. Tutkimuksen perusteella todettiin nykyaikaista ilmaisintekniikkaa käyttävän PET-TT-kameran suorituskyvyn olevan parempi verrattuna aiempaa ilmaisintekniikkaa käyttäviin PET-TT-kameroihin. Acknowledgement:: This project (15HLT05 PerfusImaging) has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme

Effect of respiratory motion correction and CT-based attenuation correction on dual-gated cardiac PET image quality and quantification

Background.Dual-gating reduces respiratory and cardiac motion effects but increases noise. With motion correction, motion is minimized and image quality preserved. We applied motion correction to create end-diastolic respiratory motion corrected images from dual-gated images.Methods.[F-18]-fluorodeoxyglucose ([F-18]-FDG) PET images of 13 subjects were reconstructed with 4 methods: non-gated, dual-gated, motion corrected, and motion corrected with 4D-CT (MoCo-4D). Image quality was evaluated using standardized uptake values, contrast ratio, signal-to-noise ratio, coefficient of variation, and contrast-to-noise ratio. Motion minimization was evaluated using myocardial wall thickness.Results.MoCo-4D showed improvement for contrast ratio (2.83 vs 2.76), signal-to-noise ratio (27.5 vs 20.3) and contrast-to-noise ratio (14.5 vs 11.1) compared to dual-gating. The uptake difference between MoCo-4D and non-gated images was non-significant (P > .05) for the myocardium (2.06 vs 2.15 g/mL), but significant (P Conclusions.End-diastolic respiratory motion correction and 4D-CT resulted in improved motion minimization and image quality over standard dual-gating.</p

Study of the Effect of Reconstruction Parameters for Myocardial Perfusion Imaging in PET With a Novel Flow Phantom

Myocardial perfusion imaging (MPI) with positron emission tomography (PET) allows quantitative temporal measurements of the radioactive tracer distribution in tissue. The quantification for myocardial blood flow (MBF) is conducted with kinetic modeling of the image-derived time-activity curves (TACs) allowing derivation for MBF in units of mL/min per gram of tissue. The ordered-subset expectation maximization (OSEM) reconstruction algorithm with time-of-flight (TOF) and point spread function (PSF) modeling is now routinely employed in cardiac imaging. However, the varying counting statistics of the MPI measurements conducted with short-lived tracers present a challenge for the PET image reconstruction methods. Thus, the effect of the reconstruction methods on the flow quantification needs to be evaluated in a standardized manner. Recently, a novel PET flow phantom modeling the MBF has been developed for investigation of the standardization of the MBF measurements. In this study, the effect of the reconstruction parameters on the image-derived flow values against a known reference flow of the flow phantom was studied with [O-15]H2O. The effects were studied by comparison of TACs and relative errors of the image-derived flow values with respect to the phantom-derived reference flow value using 5 repeated PET scans with fixed acquisition parameters using a digital Discovery MI PET/CT system. The reconstruction methods applied were OSEM using both TOF and PSF (OSEM-TOF-PSF) with several matrix sizes (128 x 128, 192 x 192, 256 x 256, 384 x 384), Gaussian filter sizes (4, 8 mm) and OSEM without TOF and PSF (OSEM), with TOF (OSEM-TOF) and with PSF (OSEM-PSF) in addition to recently introduced regularized reconstruction method based on Bayesian-penalized maximum likelihood (Q.Clear). Between repeated measurements, the image-derived flow values showed high repeatability with a SD less than 2 mL/min as well as high accuracy with the maximum error of 7% with respect to the reference flow for all reconstructions. Overall, reconstruction settings had only a small impact on the resulting flow values. In conclusion, due to the small differences detected, any of the implemented reconstruction algorithms on the system can be applied in MPI studies for accurate flow quantification

Measurement uncertainty quantification for myocardial perfusion using cardiac positron emission tomography imaging

Perfusion, the flow of blood, and hence oxygen, is essential to the functioning of the heart. Reduced perfusion (or ischemia), is a reliable indicator of the presence of significant obstructive coronary artery disease (CAD), which is one of the biggest causes of death in Europe. Myocardial perfusion imaging is a non-invasive technique used in the diagnosis, management and prognosis of CAD and is a key component in the triage of patients into treatment and non-treatment groups. Cardiac positron emission tomography (PET) is an imaging technique with high sensitivity and specificity to CAD, however perfusion measurements are difficult to calibrate against a common reference standard, and confidence in them is generally not quantified in terms of measurement uncertainty. There are a number of steps involved in measuring perfusion using cardiac PET-from patient preparation to data analysis-each associated with potential sources of uncertainty. The absence of measurement uncertainty quantification can lead to inaccuracies in measurement results, a lack of comparability between devices or scanning facilities, and is likely to be detrimental to a decision-making process. In this paper, we identify some of the sources of measurement uncertainty in the cardiac PET perfusion measurement pipeline. We assess their relative contribution by performing a sensitivity analysis using experimental data of a flow phantom acquired on a PET scanner. The results of this analysis will inform users of how parameter choices in their imaging pipeline affect the output of their measurements, and serves as a starting point to develop an uncertainty quantification method.</p

A Respiratory Motion Estimation Method Based on Inertial Measurement Units for Gated Positron Emission Tomography

We present a novel method for estimating respiratory motion using inertial measurement units (IMUs) based on microelectromechanical systems (MEMS) technology. As an application of the method we consider the amplitude gating of positron emission tomography (PET) imaging, and compare the method against a clinically used respiration motion estimation technique. The presented method can be used to detect respiratory cycles and estimate their lengths with state-of-the-art accuracy when compared to other IMU-based methods, and is the first based on commercial MEMS devices, which can estimate quantitatively both the magnitude and the phase of respiratory motion from the abdomen and chest regions. For the considered test group consisting of eight subjects with acute myocardial infarction, our method achieved the absolute breathing rate error per minute of 0.44 +/- 0.23 1/min, and the absolute amplitude error of 0.24 +/- 0.09 cm, when compared to the clinically used respiratory motion estimation technique. The presented method could be used to simplify the logistics related to respiratory motion estimation in PET imaging studies, and also to enable multi-position motion measurements for advanced organ motion estimation.</p

Assessment of a digital and an analog PET/CT system for accurate myocardial perfusion imaging with a flow phantom

In Myocardial Perfusion Imaging (MPI) with Positron Emission Tomography/Computed Tomography (PET/CT) systems, accurate quantification is essential. We assessed flow quantification accuracy over various injected activities using a flow phantom.Methods The study was performed on the digital 4-ring Discovery MI (DMI-20) and analog Discovery 690 (D690) PET/CT systems, using 325-1257 MBq of [O-15]H2O. PET performance and flow quantification accuracy were assessed in terms of count-rates, dead-time factors (DTF), scatter fractions (SF), time-activity curves (TACs), areas-under-the-curves (AUCs) and flow values.Results On DMI-20, prompts of 12.8 Mcps, DTF of 2.06 and SF of 46.1% were measured with 1257 MBq of activity. On the D690, prompts of 6.85 Mcps, DTF of 1.57 and SF of 32.5% were measured with 1230 MBq of activity. AUC values were linear over all activities. Mean wash-in flow error was - 9% for both systems whereas wash-out flow error was - 5% and - 6% for DMI-20 and D690. With the highest activity, wash-out flow error was - 12% and - 7% for the DMI-20 and D690.Conclusion DMI-20 and D690 preserved accurate flow quantification over all injected activities, with maximum error of - 12%. In the future, flow quantification accuracy over the activities and count-rates evaluated in this study should be assessed