Piotr J. Slomka

Multimodality image registration with software: state-of-the-art

IntroductionMultimodality image integration of functional and anatomical data can be performed by means of dedicated hybrid imaging systems or by software image co-registration techniques. Hybrid positron emission tomography (PET)/computed tomography (CT) systems have found wide acceptance in oncological imaging, while software registration techniques have a significant role in patient-specific, cost-effective, and radiation dose-effective application of integrated imaging.ObjectivesSoftware techniques allow accurate (2–3xa0mm) rigid image registration of brain PET with CT and MRI. Nonlinear techniques are used in whole-body image registration, and recent developments allow for significantly accelerated computing times. Nonlinear software registration of PET with CT or MRI is required for multimodality radiation planning. Difficulties remain in the validation of nonlinear registration of soft tissue organs. The utilization of software-based multimodality image integration in a clinical environment is sometimes hindered by the lack of appropriate picture archiving and communication systems (PACS) infrastructure needed to efficiently and automatically integrate all available images into one common database.DiscussionIn cardiology applications, multimodality PET/single photon emission computed tomography and coronary CT angiography imaging is typically not required unless the results of one of the tests are equivocal. Software image registration is likely to be used in a complementary fashion with hybrid PET/CT or PET/magnetic resonance imaging systems. Software registration of stand-alone scans “paved the way” for the clinical application of hybrid scanners, demonstrating practical benefits of image integration before the hybrid dual-modality devices were available.

Combined quantitative analysis of attenuation corrected and non-corrected myocadial perfusion SPECT: Method development and clinical validation

BackgroundAttenuation corrected myocardial perfusion SPECT (AC-MPS) has been demonstrated to improve the specificity of detecting coronary artery disease (CAD) by visual analysis which utilizes both non-corrected (NC) and AC data. However, the combined automated quantification of NC and AC-MPS has not been previously described. We aimed to develop a combined quantitative analysis from AC and NC data to improve the accuracy of automated detection of CAD from AC-MPS.MethodsStress total perfusion deficit (TPD) values were generated by standard analysis for NC (NC-TPD), AC (AC-TPD) and by combined NC-AC analysis (NA-TPD), in which the hypoperfusion severity in each polar map location was defined as the average of AC and NC severity computed by comparison with separate AC and NC normal limits. Ischemic TPD was also calculated as the difference between stress TPD and rest TPD for each measure. Stress/rest Tc-99m sestamibi MPS studies in 650 patients with correlating coronary angiography and in 345 patients with a low-likelihood (LLk) of CAD were used to assess diagnostic performance of combined NC-AC analysis.ResultsNA-TPD had a higher receiver-operator-characteristic area under the curve (ROC-AUC) (0.87) than NC-TPD (0.85; Pxa0<xa0.01) or AC-TPD (0.85; Pxa0<xa0.01) for detection of stenosis ≥70% in angiographic group. It also had higher specificity (75%) vs NC-TPD (65%; Pxa0<xa0.0001), or AC-TPD (70%; Pxa0=xa0.016). In LLk group, the normalcy rate of NA-TPD (95%) was higher than for NC-TPD (90%; Pxa0<xa0.01) and similar to AC-TPD (94%; Pxa0=xa0NS). NA-TPD had higher ROC-AUC than that for 17-segment expert visual scoring of stress scans in angiographic group (0.84; Pxa0=xa0.01), comparable accuracy (81%) and similar normalcy rates (95% vs 97%; Pxa0=xa0NS). Ischemic TPD by combined NC-AC analysis had higher ROC-AUC than that for any ischemic measure. Similar to stress NA-TPD, it also obtained the similar performance results as compared with ischemic TPD based on NC or AC and higher sensitivity (89% vs 85%; Pxa0=xa0.0295) as compared with ischemic visual score in angiographic group.ConclusionCombined NC-AC MPS quantification using either stress or ischemic TPD shows significant improvements for ROC-AUC and specificity of MPS in the detection of CAD compared with standard NC-MPS or AC-MPS and comparable performance to expert visual scoring. This technique may lead to an enhancement in a fully automated quantification for the perfusion analysis by AC-MPS.

Fully automated wall motion and thickening scoring system for myocardial perfusion SPECT: method development and validation in large population

BackgroundObjective assessment of wall motion (M) and thickening (T) will aid in diagnosis of coronary artery disease (CAD) from myocardial perfusion SPECT (MPS). We aimed to develop and validate an improved fully automated M/T segmental scoring system for MPS.Methods100 normal gated stress/rest Tc-99m sestamibi MPS scans from patients with low-likelihood (LLk) of CAD were used to derive the regional normal M/T ranges. A new automatic algorithm incorporated regional dependence on the global contractility in polar map coordinates by linear regression analysis and automatically derived 17-segment M (scale 0-5) and T (scale 0-3) scores. We validated this new method in 630 consecutive Tc-99m stress MPS studies in patients with suspected CAD and available correlating angiography, and an additional 241 LLk studies. Two independent observers with 12 and 30xa0years of experience in nuclear cardiology, blinded to clinical and angiographic data, scored M /T in 17-segments for all 971 studies.ResultsComputation time was <1xa0s per case. In the angiography group, there was a high correlation between the summed scores (averaged for two observers) and automatic scores with rxa0=xa00.91 (slopexa0=xa01.02, offsetxa0=xa00.2; Pxa0<xa0.0001) for M and rxa0=xa00.88 (slopexa0=xa01.06, offsetxa0=xa00.28 for T; Pxa0<xa0.0001). Weighted kappa was 0.63 for M and 0.57 for T, with expected agreement of 89% (M) and 91% (T) in individual segments (nxa0=xa010710). Weighted kappa between two experts was 0.45 for M and 0.52 for T. The normalcy rate in LLk cases was 96% for automated M and 99% for T (summed score <3). Detection of the angiographically significant disease by automated M or T scoring was better than or equivalent to individual expert observer scoring, and better than the previous automated system.ConclusionsFully automated scoring of MPS regional ventricular function can be performed rapidly, is highly correlated with expert visual scoring, can outperform individual experienced observers in the detection of CAD by wall thickening from MPS, and avoids inter-observer variability.

Prognostic value of automated vs visual analysis for adenosine stress myocardial perfusion SPECT in patients without prior coronary artery disease: A case-control study

PurposeWe aimed to evaluate the prognostic value of automated quantitative hypoperfusion parameters derived from adenosine stress myocardial perfusion SPECT (MPS) for predicting sudden or cardiac death (CD) in case-controlled patients with suspected coronary artery disease (CAD).MethodsWe considered patients with available adenosine stress Tc-99m sestamibi MPS scans and follow-up information. 81 CD patients from a registry of 428 patients documented by the National Death Index were directly matched in a retrospective case-control design to patients without CD by key clinical parameters (age by deciles, gender, no early revascularization, pre-test likelihood categories, diabetes, and chest pain symptoms). Multivariable analysis of stress MPS total perfusion deficit (STPD) and major clinical confounders were used as predictors of CD. Visual 17-segment summed stress segmental scores (VSSS) obtained by an expert reader, were compared to STPD.ResultsCD patients had higher stress hypoperfusion measures compared to controls [STPD: 7.0% vs 3.6% (Pxa0<xa0.05), VSSS: 5.3 vs 2.1 (Pxa0<xa0.05)]. By univariate analysis, STPD and VSSS have similar predictive power (the areas under receiver operator characteristics curves: STPDxa0=xa00.64, VSSSxa0=xa00.63; Kaplan-Meier models: χ2xa0=xa07.59, Pxa0=xa0.0059 for STPD and χ2xa0=xa011.10, Pxa0=xa0.0009 for VSSS). The multiple Cox proportional hazards regression models with continuous perfusion measures showed that STPD had similar power to normalized VSSS as a predictor for CD (χ2xa0=xa04.92; Pxa0=xa0.027) vs (χ2xa0=xa08.90; Pxa0=xa0.003).ConclusionsQuantitative analysis is comparable to expert visual scoring in predicting CD in a case-controlled study.

Normal Databases for the Relative Quantification of Myocardial Perfusion

Purpose of ReviewMyocardial perfusion imaging (MPI) with SPECT is performed clinically worldwide to detect and monitor coronary artery disease (CAD). MPI allows an objective quantification of myocardial perfusion at stress and rest. This established technique relies on normal databases to compare patient scans against reference normal limits. In this review, we aim to introduce the process of MPI quantification with normal databases and describe the associated perfusion quantitative measures that are used.Recent FindingsNew equipment and new software reconstruction algorithms have been introduced, which require the development of new normal limits. The appearance and regional count variations of normal MPI scans may differ between these new scanners and standard Anger cameras. Therefore, these new systems may require the determination of new normal limits to achieve optimal accuracy in relative myocardial perfusion quantification. Accurate diagnostic and prognostic results rivaling those obtained by expert readers can be obtained by this widely used technique.SummaryThroughout this review, we emphasize the importance of the normal databases and the need for specific databases relative to distinct imaging procedures. Use of appropriate normal limits allows optimal quantification of MPI by taking into account subtle image differences due to the hardware and software used, and the population studied.

Enhancing Cardiac PET by Motion Correction Techniques

Purpose of ReviewCardiac positron emission tomography (PET) images often contain errors due to cardiac, respiratory, and patient motion during relatively long image acquisition. Advanced motion compensation techniques may improve PET spatial resolution, eliminate potential artifacts, and ultimately improve the research and clinical capabilities of PET.Recent FindingsCombined cardiac and respiratory gating has only recently been implemented in clinical PET systems. Considering that the gated image bins contain much lower counts than the original PET data, they need to be summed after correcting for motion, forming motion-corrected, high-count image volume. Furthermore, automated image registration techniques can be used to correct for motion between CT attenuation scan and PET acquisition.SummaryWhile motion correction methods are not yet widely used in clinical practice, approaches including dual-gated non-rigid motion correction and the incorporation of motion correction information into the reconstruction process have the potential to markedly improve cardiac PET imaging.