Selective Pulse Research Articles

Active Optimization Method for Power Loss Distribution in T-Type Three-Level Converter Under Half-Wave Symmetry SHEPWM

For high-power converters, it is an important task to optimize the power loss in switching devices. The total power loss affects the efficiency and cooling design of converters, and the uneven power loss distribution causes the switching devices with the highest power loss to age prematurely and shorten the lifespan. Although some low switching frequency modulation strategies can decrease the total power loss, they are not able to balance the power loss distribution. On the contrary, some approaches can balance the power loss distribution by the software and hardware redundancy states of converters only under a high switching frequency. It results in an inability to reduce the total power loss. Therefore, this article proposes an active optimization method for T-type three-level converters to deal with the uneven power loss distribution under a relatively low switching frequency. By analyzing the inner connection between the power loss distribution and 3-order component, the constraint equations of half-wave symmetry selective harmonic elimination pulse width modulation (SHEPWM) are actively redesigned. Thus, both optimization objectives of the power loss can be achieved simultaneously under the proposed SHEPWM. Some numerical analysis and experimental results are given to demonstrate the correctness and feasibility of the proposed method.

Sound processing in the cricket brain: evidence for a pulse duration filter.

The auditory system of female crickets allows them to specifically recognize and approach the species-specific male calling song, defined by sound pulses and silent intervals. Auditory brain neurons form a delay-line and coincidence detector network tuned to the pulse period of the male song. We analyzed the impact of changes in pulse duration on the behavior and the responses of the auditory neurons and the network. We confirm that the ascending neuron AN1 and the local neuron LN2 copy the temporal structure of the song. During ongoing long sound pulses, the delay-line neuron LN5 shows additional rebound responses and the coincidence detector neuron LN3 can generate additional bursts of activity, indicating that these may be driven by intrinsic oscillations of the network. Moreover, the response of the feature detector neuron LN4 is shaped by a combination of inhibitory and excitatory synaptic inputs, and LN4 responds even to long sound pulses with a short depolarization and burst of spikes, like to a sound pulse of natural duration. This response property of LN4 indicates a selective auditory pulse duration filter mechanism of the pattern recognition network, which is tuned to the duration of natural pulses. Comparing the tuning of the phonotactic behavior with the tuning of the local auditory brain neurons to the same test patterns, we find no evidence that a modulation of the phonotactic behavior is reflected at the level of the feature detector neurons. This rather suggests that steering to nonattractive pulse patterns is organized at the thoracic level.NEW & NOTEWORTHY Pulse period selectivity has been reported for the cricket delay-line and coincidence detector network, whereas pulse duration selectivity is evident from behavioral tests. Pulses of increasing duration elicit responses in the pattern recognition neurons, which do not parallel the behavioral responses and indicate additional processing mechanisms. Long sound pulses elicit rhythmic rebound activity and additional bursts, whereas the feature detector neuron reveals a pulse duration filter, expanding our understanding of the pattern recognition process.

Nuclear Magnetic Resonance for Targeted Metabolomics and Biochemical Sensor

NMR spectroscopy is quantitative, highly reproducible, non-selective and non-destructive. However, NMR costs and complexity hinder a use as point-of-care and biochemical sensor instrumentation. Low field NMR (LF-NMR) is an inexpensive and low footprint technique to obtain physical, chemical, electronic and structural information on small molecules, but suffers from poor spectral dispersion, especially when applied to the analysis of mixtures. Subspectral editing employing optimal control pulses is a suitable approach to cope with the severe signal superpositions in complex mixture spectra at low field.
 We have calculated the optimal control pulse shapes at 0.5 T NMR frequency using the Krotov algorithm. Downsizing the complexity of the algorithm from exponential to polynomial is shown to be possible by using a system approach with each system corresponding to a (small) molecule. In this way compound selective excitation pulses can be calculated. The signals of substructures of the cyclopentenone molecule were excited using optimal control pulses calculated by the Krotov algorithm demonstrating the feasibility of subspectral editing. Likewise, for a mixture of benzoic acid and alanine, editing of the signals of either benzoic acid or alanine employing optimal control pulses was shown to be possible.
 The obtained results are promising and can be extended to the targeted analysis of complex mixtures such as biofluids or metabolic samples at low field strengths opening access for benchtop NMR to point of care settings. Moreover, the LF-NMR was improved to allow a unique detection and reliable quantification of metabolites in biofluids like blood, urine, cerebrospinal fluid, or even tissue. In contrast to standard large scale NMR equipment the portable LF-NMR allows for an analysis of the chemical composition of biofluid samples directly at the patient (point-of-care).
 LF-NMR can be freely programmable for detecting and detecting and sensing sets of small molecules which deliver information on the health status of a person. Such an analytical tool would be useful for the prediction, diagnosis, monitoring and prognosis of diseases, and for supervision of therapeutic interventions.

Spatiotemporal 1H NMR Spectroscopy of 3D Cell Models

The emergence of three-dimensional cell cultures representing tissue features closely, that are weakly reproduced by standard two-dimensional systems, requires adapting established analytical techniques to investigate these challenging new models. It is especially desired to obtain spatially resolved data for living organoids giving insight into transport processes and biochemical characteristics of domains differently provided with nutrition supply and waste product removal. Within this work we present an NMR-based approach to dynamically obtained radial metabolite profiles for cell spheroids, one of the most frequently used 3D models. Our approach combines an easy to reproduce custom-made measurement design maintaining incubator conditions without inhibition of the NMR experiment, with a spatial selective NMR pulse sequence. To overcome the inherently low sensitivity of NMR spectroscopy we modified the selective sequence to achieve faster acquisition and employed a commercially available cryo NMR probe. Finally, radial metabolite profiles could be obtained via double Abel inversion of the measured one‑dimensional intensity profiles. Applying this method to Ty82 cancer cell spheroids clearly demonstrates the spatial resolution, for instance confirming exceedingly high lactate and strongly decreased glucose concentrations in the oxygen-depleted core of the spheroid. Furthermore, we dynamically investigate the process of cell death and metabolite degradation after maintaining a spheroid under incubator conditions for several days.

Mitigation of harmonics for five level multilevel inverter with fuzzy logic controller

Introduction. The advantages of a high-power quality waveform and a high voltage capability of multilevel inverters have made them increasingly popular in recent years. These inverters reduce harmonic distortion and improve the voltage output. Realistically speaking, as the number of voltage levels increases, so does the quality of the multilevel output-voltage waveform. When it comes to industrial power converters, these inverters are by far the most critical. Novelty. Multilevel cascade inverters can be used to convert multiple direct current sources into one direct current. These inverters have been getting a lot of attention recently for high-power applications. A cascade H-bridge multilevel inverter controller is proposed in this paper. A change in the pulse width of selective pulse width modulation modulates the output of the multilevel cascade inverter. Purpose. The total harmonic distortion can be reduced by using filters on controllers like PI and fuzzy logic controllers. Methods. The proposed topology is implemented with MATLAB/Simulink, using gating pulses and pulse width modulation methodology and fuzzy logic controllers. Moreover, the proposed model also has been validated and compared to the hardware system. Results. Total harmonic distortion, number of power switches, output voltage and number of DC sources are analyzed with conventional topologies. Practical value. The proposed topology has been very supportive for implementing photovoltaic based multilevel inverter, which is connected to large demand in grid and industry.

Efficient (2N+1) selective harmonic elimination in modular multilevel converters using an evolutionary many-tasking approach with prior knowledge

(2N+1) selective harmonic elimination pulse with modulation (SHE-PWM) is an important technique for a modular multi-level converter (MMC) to enhance the control ability and improve the fundamental wave amplitude accuracy of the output waveform. While finding optimal switch angles by solving the complex non-linear equation system is one of its main challenges. A current popular solution is to run a metaheuristic or evolutionary algorithm repeatedly on various modulation indexes. These methods ignore the fact that some of the optimization tasks are similar, and the optimization experiences could be shared among these similar tasks. To fill this gap, this study proposes an evolutionary many-tasking approach with prior knowledge (EMT-PK). EMT-PK facilitates positive knowledge transfer between similar tasks and is capable to solve all the sub SHE-PWM problems simultaneously through a single run. Numerical results on 7-, 9- and 11-level MMCs show that EMT-PK provides superior results for the (2N+1) SHE-PWM in comparison with 8 other widely used metaheuristics/evolutionary algorithms in this field including differential evolution (DE), ant colony optimization (ACO), teaching and learning-based optimization (TLBO), bee algorithm (BA), genetic algorithm (GA), particle swarm optimization (PSO), generalized pattern search (GPS) and asynchronous particle swarm optimization-genetic algorithm(APSO-GA). The superior performance of EMT-PK is further validated by the MATLAB Simulink simulation and the laboratory experiment on a 7-level MMC.

Echo pulses for background suppression by optimal control.

Materials used to construct magic-angle-spinning NMR probes can contain NMR active nuclei that produce a significant amount of background signal. Because these materials are located outside the sample coil, the use of spatially selective pulses to remove the background is a popular approach for background suppression. However, previously suggested spatially selective pulses suffer from limited excitation bandwidths, which may make them unsuitable for the acquisition of nuclei with a large chemical shift range. Here, a pulse (OC-BACK) is presented, which has been developed by optimal control, which has a flat profile of ~120 kHz with respect to off-resonance effects and extended pass and suppression bands with respect to the nominal nutation frequency. The presented solution is large enough to be effective for background suppression schemes in 19 F magic-angle-spinning NMR at medium and low magnetic fields.

SLfRank: Shinnar-Le-Roux Pulse Design With Reduced Energy and Accurate Phase Profiles Using Rank Factorization.

The Shinnar-Le-Roux (SLR) algorithm is widely used to design frequency selective pulses with large flip angles. We improve its design process to generate pulses with lower energy (by as much as 26%) and more accurate phase profiles. Concretely, the SLR algorithm consists of two steps: (1) an invertible transform between frequency selective pulses and polynomial pairs that represent Cayley-Klein (CK) parameters and (2) the design of the CK polynomial pair to match the desired magnetization profiles. Because the CK polynomial pair is bi-linearly coupled, the original algorithm sequentially solves for each polynomial instead of jointly. This results in sub-optimal pulses. Instead, we leverage a convex relaxation technique, commonly used for low rank matrix recovery, to address the bi-linearity. Our numerical experiments show that the resulting pulses are almost always globally optimal in practice. For slice excitation, the proposed algorithm results in more accurate linear phase profiles. And in general the improved pulses have lower energy than the original SLR pulses.

Runge–Kutta optimization‐based selective harmonic elimination in an H‐bridge multilevel inverter

AbstractThe application of iterative techniques for solving the Selective Harmonic Elimination Pulse Width Modulation (SHE‐PWM) problem, such as the Newton–Raphson (NR) method, can tend to get stuck at local optima in the solution space. Additionally, these methods may be sensitive to the initial value estimation of the solution. In contrast, metaheuristic approaches demonstrate resilience in seeking out the optimal solution. As such, this study utilizes the Runge–Kutta (RUN) metaheuristic optimization algorithm to demonstrate the SHE‐PWM technique in multilevel inverters (MLIs), including 5‐ and 7‐level modified H‐bridge (MHB) topology and a 9‐level asymmetric cascaded H‐bridge (CHB) inverter topology. The switching angles are obtained by varying the modulation index from 0.01 to 1.0 in steps of 0.01 for 5‐, 7‐, and 9‐level MLIs. The performance of the RUN algorithm in minimizing the total harmonic distortion (THD) value is verified through simulations in MATLAB/Simulink software. The superiority of RUN is established by comparing the results with state‐of‐the‐art metaheuristic algorithms, such as the Differential Evolution (DE), Genetic Algorithm (GA), and Grey Wolf Optimizer (GWO). Additionally, the switching angles obtained through RUN are validated by hardware experiments. According to the simulation and experimental results, the proposed RUN method exhibits better performance in terms of objective function values, algorithm robustness, fundamental harmonic magnitude, and THD values. The findings confirm the elimination of fifth harmonic, fifth, and seventh harmonics, and fifth, seventh, and ninth harmonics in 5‐, 7‐, and 9‐level MLIs, respectively.

Non-aqueous magnetization following adiabatic and selective pulses in brain: T1 and cross-relaxation dynamics.

Inversion pulses are commonly employed in MRI for T1 -weighted contrast and relaxation measurements. In brain, it is often assumed that adiabatic pulses saturate the non-aqueous magnetization. We investigated this assumption using solid-stateNMRto directly monitor the non-aqueous signal following adiabatic inversion and compared this to signals following hard and soft inversion pulses. The effects of the different preparations on relaxation dynamics were explored. Inversion recovery experiments were performed on ex vivo bovine and porcine brains in 360 MHz (8.4 T) and 200 MHz (4.7 T) NMR spectrometers, respectively, using broadband rectangular, adiabatic, and sinc inversion pulses as well as a long rectangular saturation pulse. Analogous human brain MRI experiments were performed at 3 T using single-slice echo-planar imaging. Relaxation data were fitted by mono- and bi-exponential decay models. Further fitting analysiswas performed using only two inversion delay times. Adiabatic and sinc inversion left much of the non-aqueous magnetization along B0 and resulted in bi-exponential relaxation. Saturation of both aqueous and non-aqueous magnetization components led to effectively mono-exponential T1 . relaxation. Typical adiabatic inversion pulses do not, as has been widely assumed, saturate the non-aqueous proton magnetization in white matter. Unequal magnetization states in aqueous and non-aqueous .H reservoirs prepared by soft and adiabatic pulses result in bi-exponential T1 . relaxation. Both pools must be prepared in the same magnetization state (e.g. saturated or inverted) in order to observe consisten mono-exponential relaxation.

An improved modulation method for modular multilevel converters based on particle swarm optimization

Modular multilevel converter (MMC) is the first topology choice for flexible DC transmission systems. This paper presents a particle swarm optimization (PSO) algorithm aided modulation method to calculate the improved selective harmonic elimination pulse width modulation (iSHE-PWM) switching angles with the aim of reducing the total harmonic distortion (THD) and output voltage error of MMC. The SHE-PWM has more controllable variables compared with the staircase modulation so that it can be used to improve the output current waveform quality. This method retains the advantages of easy to control and low frequency from the staircase modulation. But amplitude of its high-order harmonic is high and this paper improves it. Firstly the mathematical model of MMC is set up and corresponding expressions of THD and voltage error are given. The joint function of THD and voltage error is considered as the fitness function. The PSO algorithm was used to minimize the joint function for solving the optimal switching angles. Finally the proposed method is verified through simulation results showing its potential to successfully solve the problem of difficulty in obtaining the iSHE-PWM switching angles while minimizing the THD and output voltage error of the MMC.

The Use of Highly Selective Radio-Frequency Pulses for Magnetic Resonance Imaging of the Mammary Glands

The Use of Highly Selective Radio-Frequency Pulses for Magnetic Resonance Imaging of the Mammary Glands

Acceleration of indirect detection 195Pt solid-state NMR experiments by sideband selective excitation or alternative indirect sampling schemes

The measurement of the of chemical shift (CS) tensors via solid-state NMR (ssNMR) spectroscopy has proven to be a powerful probe of structure for organic molecules, biomolecules, and inorganic materials. However, when measuring the NMR spectra of heavy spin-1/2 isotopes the chemical shift anisotropy (CSA) is commonly on the order of thousands of parts per million, which makes acquisition of NMR spectra difficult due to the low NMR sensitivity imposed by the breadth of the signals and challenges in uniformly exciting the NMR spectrum. We have recently shown that complete 195Pt NMR spectra could be rapidly measured by using 195Pt saturation or excitation selective long pulses (SLP) with multiple rotor-cycle durations and RF fields less than 50 kHz into 1H{195Pt} or 1H-31P{195Pt} PE S-RESPDOR, TONE D-HMQC-4, J-resolved, and J-HMQC pulse sequences. The SLP only provide signal or dephasing when they are applied on resonance with a spinning sideband. The magic angle spinning 195Pt NMR spectrum is reconstructed in the sideband selective NMR experiments by acquiring 1D NMR spectra at variable 195Pt pulse offsets. In this work, we present a detailed investigation of the specific pulse conditions required for the ideal performance of sideband selective experiments. Sideband selective experiments are shown to be able to accurately reproduce MAS NMR spectra with minimal distortions of relative sideband intensities. It is also demonstrated that a 195Pt NMR spectrum indirectly detected with HMQC can be rapidly obtained by acquiring a single rotor cycle of indirect dimension evolution points. We dub this method One Rotor Cycle of Acquisition (ORCA) HMQC. Sideband selective experiments and ORCA HMQC experiments are shown to provide a one order of magnitude improvement in experiment times as compared to conventional wideline HMQC experiments.

Hybrid low switching frequency modulation strategy with high dynamic response for high‐power voltage source converter

AbstractFor high‐power converters, the low switching frequency (SF) modulation represented by selective harmonic elimination pulse width modulation (SHE‐PWM) is crucial to reduce the switching loss and enhance the efficiency with a good steady‐state performance. However, since the advantages of SHE‐PWM mainly come from the fixed switching angle distribution limited by non‐linear equations, switching angles should be adjusted slowly. This requires that the bandwidth of proportional integral (PI) controllers be limited hugely, resulting in a poor dynamic response. As the most popular control to improve the dynamic response, finite‐control‐set model predictive control (FCS‐MPC) has a worse steady‐state performance under low SF because of large errors caused by a long prediction period and harmonics caused by space vector PWM (SVPWM). Therefore, a hybrid modulation strategy with an acceptable complexity is proposed in this article, which combines SHE‐PWM and FCS‐MPC. PI + SHE‐PWM is adopted in a steady state with low SF, while MPC + SVPWM is used in a transient state with high SF. By studying smooth switching from the modulation level and control level, the proposed method can eliminate the current surge when switching between PI + SHE‐PWM and MPC + SVPWM. Experiments verify that the proposed method have a good steady‐state performance and high dynamic response simultaneously under overall low SF.

Quantum Gate Operations on a Spectrally Addressable Photogenerated Molecular Electron Spin-Qubit Pair

Sub-nanosecond photodriven electron transfer from a molecular donor to an acceptor can be used to generate a radical pair (RP) having two entangled electron spins in a well-defined pure initial singlet quantum state to serve as a spin-qubit pair (SQP). Achieving good spin-qubit addressability is challenging because many organic radical ions have large hyperfine couplings (HFCs) in addition to significant g-anisotropy, which results in significant spectral overlap. Moreover, using radicals with g-factors that deviate significantly from that of the free electron results in difficulty generating microwave pulses with sufficiently large bandwidths to manipulate the two spins either simultaneously or selectively as is necessary to implement the controlled-NOT (CNOT) quantum gate essential for quantum algorithms. Here, we address these issues by using a covalently linked donor-acceptor(1)-acceptor(2) (D-A1-A2) molecule with significantly reduced HFCs that uses fully deuterated peri-xanthenoxanthene (PXX) as D, naphthalenemonoimide (NMI) as A1, and a C60 derivative as A2. Selective photoexcitation of PXX within PXX-d9-NMI-C60 results in sub-nanosecond, two-step electron transfer to generate the long-lived PXX•+-d9-NMI-C60•- SQP. Alignment of PXX•+-d9-NMI-C60•- in the nematic liquid crystal 4-cyano-4'-(n-pentyl)biphenyl (5CB) at cryogenic temperatures results in well-resolved, narrow resonances for each electron spin. We demonstrate both single-qubit gate and two-qubit CNOT gate operations using both selective and nonselective Gaussian-shaped microwave pulses and broadband spectral detection of the spin states following the gate operations.

A strategy for improving the SHEPWM commutation speed of CSI through hybrid switches

High-power current source inverters (CSI) usually operate at a low switching frequency to reduce switching loss. To suppress low-order harmonics and simplify filter design, the selective harmonic elimination pulse width modulation (SHEPWM) technique is a feasible common modulation strategy in industrial applications. This paper proposes an operational strategy that uses an H7 current source inverter (H7-CSI) with hybrid switches to perform the SHEPWM technique. On the basis of retaining the conventional H6 inverter bridge, the commutation speed of the CSI is improved by an additional shunt-connected high-performance power switch. The proposed scheme solves the problem that the CSIs built with low-speed switches (such as GTOs) may have difficulty for implementing the setting pulse widths of null states, while further reducing the switching losses at an acceptable cost. In addition, mitigating the influence of overlap-time by optimizing the driving signal of the H6 converter bridge. Finally, simulation and experiments have verified the effectiveness of the proposed CSI scheme.

Pulsed selective excitation theory and design in multiphoton MRI

Excitation in MRI is traditionally done at the Larmor frequency, where the energy of each radiofrequency photon corresponds to the energy difference between two spin states. However, if multiple radiofrequencies are employed, then multiphoton excitation can also occur when the sum or difference of multiple photon frequencies equals the Larmor frequency. Although multiphoton excitation has been known since the early days of NMR, it has been relatively unexplored in MRI. In this work, equations and principles for multiphoton selective RF pulse design in imaging are presented and experimentally demonstrated. In particular, the case where there are radiofrequency fields in both the traditional xy-direction and non-traditional z-direction is considered. To produce the z-direction radiofrequency field, an additional uniform coil was added to a clinical MRI scanner. Using this coil, two-photon slice-selective pulses were designed to be equivalent to traditional pulses, producing similar excitation, slice profiles, and in vivo images. Being the result of a combination of multiple radiofrequency fields instead of just one, two-photon pulses have more flexibility in how their parameters can be changed. Although individual multiphoton excitations are less efficient than their traditional counterparts, when the z-direction radiofrequency field is spatially non-uniform, multiple multiphoton resonances can be simultaneously used at different locations to produce simultaneous multislice excitation with the same pulse duration but less tissue heating than a naive implementation. In particular, non-uniform z-direction radiofrequency fields with negligible added tissue heating provided by oscillating the MRI scanner’s gradient fields at kilohertz frequencies were used to excite multiple slices simultaneously with less high-frequency xy-direction radiofrequency power. For an example three-slice excitation, we achieve half the xy-direction radiofrequency power compared to the naïve approach of adding three single-slice pulses. For conventional or unconventional applications, multiphoton excitation may be of interest when designing new MRI systems.

Harmonics Elimination in 7-Level Multilevel Inverter Using Animal Migration Optimization Algorithm with Different Objective Functions

Harmonics can degrade the power quality of a multilevel inverter by causing the voltage to be distorted and vary from sinusoidal waveforms. Harmonics can be reduced by increasing the number of voltage levels or by employing suitable modulation techniques. In this paper, The Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) modulation method is employed to obtain the optimal switching angles that able to reduce the specific individual harmonic and the Total Harmonic Distortion (THD) in singlephase 7-level Cascaded H-Bridge multilevel inverter. The Animal Migration Optimization (AMO) is proposed to acquire these angles using two difference objective functions. The performance is examined and evaluated. Both objective functions able to determine the optimal switching angles starting from modulation index of 0.34. However, the comparative study demonstratethat objective function number 2 has better performance in term of lowering selective individual harmonics as well as THD.

Current trends in ŒNO-NMR based metabolomics

Present work discusses strengths and limitations of two Nuclear Magnetic Resonance outliers obtained with a water-to-ethanol solvent multi pre saturation acquisition method, recently included in the Compendium of International Methods of Analysis of Wines and Musts, published as OIV-MA-AS316-01, and their accuracy for metabolomics analysis. Furthermore, it is also presented an alternative to produce more discriminant and sensitive NMR data matrices for metabolomics studies, comprising the use of a novel NMR acquisition strategy in wines, the double pulsed-field gradient echo (DPFGE) NMR scheme, with a refocusing band-selective uniform-response pure-phase selective pulse, for a selective excitation of the 5-10 ppm chemical shift range of wine samples, that reveals novel broad aromatic 1H resonances, directly associated to complex polyphenols. Both aromatics and full binned OIV-MA-AS316-01,as well as the selective 5-10 ppm DPFGE NMR outliers were statistically analyzed with diverse non-supervised Principal Component Analysis (PCA) and supervised Partial Least Squares -Discriminant Analysis (PLS-DA), sparse (sPLS-DA) least squares- discriminant analysis, and orthogonal projections to latent structures discriminant analysis (OPLS-DA). Supervised multivariate statistical analysis of DPFGE and aromatics’ binned OIV-MA-AS316-01NMR data have shown their robustness to broadly discriminate geographical origins and narrowly differentiate between different fermentation schemes of wines from identical variety and region.

Signal-to-noise ratio penalties from a loss of stimulated echoes when using slab-selective excitation in three-dimensional fast spin echo imaging with long echo trains.

Three-dimensional fast spin echo imaging with long echo trains combines high resolution with reasonable acquisition times and reduced specific absorption rate due tolow refocusing flip angles. Typically, an entire volume is encoded (nonselective excitation) or localization can be performed with slab select excitation, which uses a long 90° pulse for precise localization, followed by a preliminary nonselective 180° pulse bounded by spoiler gradients to destroy signal outside of the volume of interest. Subsequent flip angles in the train are nonselective and identical between the two methods. The inclusion of the initial selective pulse and spoiler gradients results in a signal-to-noise ratio (SNR) penalty for slab selection, beyond the slice-averaging dependence, arising from a loss of stimulated echoes. SNR differences are explored using Bloch equation simulations of a T2-weighted 96 echo train sequence with varying parameters including T2, T1, and B1+ and compared with phantom and in vivo brain, neck, and knee experiments. In vivo SNR measurements in the three regions showed a maximum decrease of selective SNR by 29% (gastrocnemius muscle), 25% (pons), and 22% (globus pallidus), despite similar experimental parameters to nonselective experiments. Decreased SNR was compounded by B1+ variation affecting prescribedflip angles with further smaller reductions with T2 and T1 times. In conclusion, the elimination of coherences via the preliminary nominal 180° pulse and spoiler gradients in addition to the extended echo timing from the long excitation pulse resulted in a reduction in SNR compared with the nonselective case. Consideration of the required SNR and chosen anatomy as well as sequence restrictions should be weighed before choosing slab-selective excitation.