Comparative Analysis between SPECT Myocardial Perfusion Imaging and CT Coronary Angiography for Diagnosis of Coronary Artery Disease

Attributes of nuclear imaging centers impacting physician referrals for single-photon emission computed tomography myocardial perfusion imaging tests

AIM

To evaluate nuclear imaging center attributes that cardiologists and primary care physicians (PCPs) consider when referring patients for single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) tests, and how these attributes impact physician referral decisions in the United States.

METHODS

A targeted literature review and seven one-to-one interviews with physicians and imaging center directors were conducted to identify attributes that could impact physicians' referral decisions. The impact of the identified attributes was assessed via an online discrete choice survey among eligible PCPs and cardiologists randomly selected from a nationally representative panel, and quantified with an odds ratio (OR) scale estimated with a multivariable logistic regression.

RESULTS

Nine two-level attributes were identified: ease of the referral process, waiting time for tests, insurance preauthorization assistance, time to receive results, conclusive test reports, patient satisfaction, a protocol for rapid conversion from an exercise to a pharmacological stress test, patient communication, and assistance with parking/wheelchair access. A total of 410 physicians, including 208 (50.7%) cardiologists and 202 (49.3%) PCPs completed the survey. Among all physicians, a protocol that allows for a rapid conversion from an exercise to a pharmacological stress test (OR = 2.9) and preauthorization assistance (OR = 2.6) were the most impactful attributes. Additionally, cardiologists preferred imaging centers that provide an easy referral process (OR = 2.7), while PCPs favored centers offering a conclusive test report (OR = 2.4).

LIMITATIONS

Some center features that might impact physician referral decision were not evaluated in this study, if they were not easily changeable from an imaging center's perspective.

CONCLUSIONS

The availability of a protocol for rapid conversion from an exercise to a pharmacological stress test and preauthorization assistance had the most significant impact on physician referral decisions for SPECT-MPI. Additionally, cardiologists preferred centers providing an easy referral process, while PCPs favored those offering a concluding statement and actionable steps in test reports.

Optimal control design of turbo spin-echo sequences with applications to parallel-transmit systems

Purpose

The design of turbo spin‐echo sequences is modeled as a dynamic optimization problem which includes the case of inhomogeneous transmit radiofrequency fields. This problem is efficiently solved by optimal control techniques making it possible to design patient‐specific sequences online.

Theory and Methods

The extended phase graph formalism is employed to model the signal evolution. The design problem is cast as an optimal control problem and an efficient numerical procedure for its solution is given. The numerical and experimental tests address standard multiecho sequences and pTx configurations.

Results

Standard, analytically derived flip angle trains are recovered by the numerical optimal control approach. New sequences are designed where constraints on radiofrequency total and peak power are included. In the case of parallel transmit application, the method is able to calculate the optimal echo train for two‐dimensional and three‐dimensional turbo spin echo sequences in the order of 10 s with a single central processing unit (CPU) implementation. The image contrast is maintained through the whole field of view despite inhomogeneities of the radiofrequency fields.

Conclusion

The optimal control design sheds new light on the sequence design process and makes it possible to design sequences in an online, patient‐specific fashion. Magn Reson Med 77:361–373, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine

Reproducibility and optimization of in vivo human diffusion-weighted MRS of the corpus callosum at 3 T and 7 T

Diffusion-weighted MRS (DWS) of brain metabolites enables the study of cell-specific alterations in tissue microstructure by probing the diffusion of intracellular metabolites. In particular, the diffusion properties of neuronal N-acetylaspartate (NAA), typically co-measured with N-acetylaspartyl glutamate (NAAG) (NAA + NAAG = tNAA), have been shown to be sensitive to intraneuronal/axonal damage in pathologies such as stroke and multiple sclerosis. Lacking, so far, are empirical assessments of the reproducibility of DWS measures across time and subjects, as well as a systematic investigation of the optimal acquisition parameters for DWS experiments, both of which are sorely needed for clinical applications of the method. In this study, we acquired comprehensive single-volume DWS datasets of the human corpus callosum at 3 T and 7 T. We investigated the inter- and intra-subject variability of empirical and modeled diffusion properties of tNAA [D(avg) (tNAA) and D(model) (tNAA), respectively]. Subsequently, we used a jackknife-like resampling approach to explore the variance of these properties in partial data subsets reflecting different total scan durations. The coefficients of variation (C(V)) and repeatability coefficients (C(R)) for D(avg) (tNAA) and D(model) (tNAA) were calculated for both 3 T and 7 T, with overall lower variability in the 7 T results. Although this work is limited to the estimation of the diffusion properties in the corpus callosum, we show that a careful choice of diffusion-weighting conditions at both field strengths allows the accurate measurement of tNAA diffusion properties in clinically relevant experimental time. Based on the resampling results, we suggest optimized acquisition schemes of 13-min duration at 3T and 10-min duration at 7 T, whilst retaining low variability (C(V) ≈ 8%) for the tNAA diffusion measures. Power calculations for the estimation of D(model )(tNAA) and D(avg) (tNAA) based on the suggested schemes show that less than 21 subjects per group are sufficient for the detection of a 10% effect between two groups in case-control studies.

(1)H MR spectroscopic imaging of the prostate at 7T using spectral-spatial pulses

PURPOSE

To assess the feasibility of prostate (1)H MR spectroscopic imaging (MRSI) using low-power spectral-spatial (SPSP) pulses at 7T, exploiting accurate spectral selection and spatial selectivity simultaneously.

METHODS

A double spin-echo sequence was equipped with SPSP refocusing pulses with a spectral selectivity of 1 ppm. Three-dimensional prostate (1)H-MRSI at 7T was performed with the SPSP-MRSI sequence using an 8-channel transmit array coil and an endorectal receive coil in three patients with prostate cancer and in one healthy subject. No additional water or lipid suppression pulses were used.

RESULTS

Prostate (1)H-MRSI could be obtained well within specific absorption rate (SAR) limits in a clinically feasible time (10 min). Next to the common citrate signals, the prostate spectra exhibited high spermine signals concealing creatine and sometimes also choline. Residual lipid signals were observed at the edges of the prostate because of limitations in spectral and spatial selectivity.

CONCLUSION

It is possible to perform prostate (1)H-MRSI at 7T with a SPSP-MRSI sequence while using separate transmit and receive coils. This low-SAR MRSI concept provides the opportunity to increase spatial resolution of MRSI within reasonable scan times.