Combination of multichannel single‐voxel MRS signals using generalized least squares

Purpose:

To propose using the generalized least square (GLS) algorithm for combining multichannel single‐voxel magnetic resonance spectroscopy (MRS) signals.

Materials and Methods:

Phantom and in vivo brain MRS experiments on a 7 T scanner equipped with a 32‐channel receiver coil, as well as Monte Carlo simulations, were performed to compare the coefficient of variation (CV) of the GLS method with those of two recently reported spectral combination methods.

Results:

Compared to the two existing methods, the GLS method significantly reduced CV values for the simulation, phantom, and in vivo experiments.

Conclusion:

The GLS method can lead to improved precision of peak quantification. J. Magn. Reson. Imaging 2013;37:1445–1450. © 2012 Wiley Periodicals, Inc.     

Predicting Perception in Noise Using Cortical Auditory Evoked Potentials

Speech perception in background noise is a common challenge across individuals and health conditions (e.g., hearing impairment, aging, etc.). Both behavioral and physiological measures have been used to understand the important factors that contribute to perception-in-noise abilities. The addition of a physiological measure provides additional information about signal-in-noise encoding in the auditory system and may be useful in clarifying some of the variability in perception-in-noise abilities across individuals. Fifteen young normal-hearing individuals were tested using both electrophysiology and behavioral methods as a means to determine (1) the effects of signal-to-noise ratio (SNR) and signal level and (2) how well cortical auditory evoked potentials (CAEPs) can predict perception in noise. Three correlation/regression approaches were used to determine how well CAEPs predicted behavior. Main effects of SNR were found for both electrophysiology and speech perception measures, while signal level effects were found generally only for speech testing. These results demonstrate that when signals are presented in noise, sensitivity to SNR cues obscures any encoding of signal level cues. Electrophysiology and behavioral measures were strongly correlated. The best physiological predictors (e.g., latency, amplitude, and area of CAEP waves) of behavior (SNR at which 50 % of the sentence is understood) were N1 latency and N1 amplitude measures. In addition, behavior was best predicted by the 70-dB signal/5-dB SNR CAEP condition. It will be important in future studies to determine the relationship of electrophysiology and behavior in populations who experience difficulty understanding speech in noise such as those with hearing impairment or age-related deficits.     

Spontaneous cries can alter the physiological well-being and cerebral oxygenation of very preterm infants

Introduction

Infant crying is a major expression of distress and can occur without any exogenous stimulation. Little is known, however, about the effects of crying on physiological homeostasis in very preterm infants (VPIs).

Methods

Environmental, behavioral (video and audio recording) and physiologic (heart rate [HR], respiratory rate [RR], and systemic [SaO₂] and regional cerebral oxygenation [rSO₂]) parameters were prospectively evaluated over 10 h in 18 VPIs (median gestational age, 28 [27–31] weeks). Only episodes of “spontaneous” and isolated cries were analyzed. Changes in parameters were compared over 5-second periods between baselines and 40 s following the onset of crying. Two periods were distinguished: 0–20 s (a) and 20–40 s (b). Minimal and/or maximal values in these periods were also compared to the baseline.

Results

Of the 18 VPIs initially studied, 13 (72%) presented crying episodes (CE). They experienced 210 “spontaneous” and isolated CE, with a median of 9 [range, 1–63] CEs per child. Physiological values varied significantly from the baseline with mainly a mean decrease in HR of − 4.8 ± 5.3 beats/min (b) after an initial mean increase of + 2.6 ± 2.0 beats/min (a); a mean decrease in RR of − 3.8 ± 4.8 cycles/min (a), followed by a mean increase of + 5.6 ± 7.3 cycles/min (b) and mean unidirectional decreases in SaO₂ and rSO₂ (minimal values) of − 1.8 ± 2.3% and − 2.5 ± 3.0%, respectively.

Conclusion

Spontaneous cries can alter the homeostasis of VPIs. Their possible adverse consequences and high occurrence emphasize the need for better prevention and response to them.     

Boosting 19F MRI—SNR efficient detection of paramagnetic contrast agents using ultrafast sequences

¹⁹F MRI offers high specificity but usually low sensitivity. Here, paramagnetic relaxation enhancement is assessed as a method to improve SNR efficiency in ¹⁹F MRI. Compounds with short relaxation times are used that combine fluorine and a paramagnetic ion within the same molecule. Different molecular designs provide T₁ values in the range of 1.4–15 ms and /T₁ ratios from 0.3 to 1. Gradient echo, as well as ultrafast radial MR sequences, is optimized to achieve highest SNR efficiency. Compared to nonparamagnetic compounds, ultrafast sequences can yield a gain of up to a factor 27 in sensitivity, whereas the gain with gradient echo is only factor 11. Comparison among the paramagnetic compounds shows that /T₁ close to unity is a prerequisite for highest SNR efficiency gain and that best results are obtained for compounds with T₁ in the range of 1–5 ms. Magn Reson Med 69:1056–1062, 2013. © 2012 Wiley Periodicals, Inc.     

Otoacoustic emissions in newborn hearing screening: A systematic review of the effects of different protocols on test outcomes

Background and objectives

Otoacoustic emission (OAE) tests are currently used to screen newborns for congenital hearing loss in many Universal Newborn Hearing Screening programs. However, there are concerns about high referral and false-positive rates. Various protocols have been used to address this problem. The main objective of this review is to determine the effects of different screening protocols on the referral rates and positive predictive values (PPV) of the OAE newborn screening test.

Methods

Eligible studies published in English from January 1990 until August 2012 were identified through searches of MEDLINE, Medline In-Process, Embase, PubMed (NCBI), ISI Web of Science, and the Cochrane Central Register of clinical controlled trials. Two reviewers independently screened the data sources, using pre-defined inclusion criteria to generate a list of eligible articles. Data extracted included the number of newborns screened, age at screening, OAE pass criteria, frequencies screened, number of retests, referral rates, and the number of newborns identified with permanent congenital hearing loss.

Results

Ten articles met the inclusion criteria, with a total of 119,714 newborn participants. The pooled referral rate was 5.5%. Individual referral rates ranged from 1.3% to 39%; the PPV from 2 to 40%. Increasing the age at initial screening and performing retests reduced the referral rate. Likewise, screenings involving higher frequencies had lower referral rates.

Conclusion

Delaying newborn hearing screening improves test results but may not be practical in all contexts. The use of higher frequencies and more sophisticated OAE devices may be useful approaches to ensure better performance of the OAE test in newborn hearing screening.     

The role of MR diffusion in differentiation of malignant and benign hepatic focal lesions

Aim

To determine if focal liver masses could be differentiated as benign or malignant by DWI and ADC maps.

Methods and materials

Sixty focal liver lesions were scanned using 1.5 T MRI. DWI was performed with b 0, b 500 and b 1000 gradients with ADC measurements. Comparison of mean ADC values between each benign and malignant lesion was done. Reference standard of diagnosis was obtained by correlating DWI with histopathologic findings and imaging follow-up. The accuracies of DWI and ADC values were assessed with the Student’s t test, and cut-off values were determined with receiver operating characteristic curve analysis.

Results

When ADC value of 1.0 × 10⁻³ mm²/s was used as a threshold value for differentiation of malignant tumors from benign lesions, sensitivity was 90.3%, specificity 78.57% and accuracy 86.7%. The best result was obtained with the use of ADC cut off value (at b 500) of 1.5 × 10⁻³ mm²/s and ADC cut off value (at b 1000) of 1.0 × 10⁻³ mm²/s, with 90.3% sensitivity, 92.86% specificity, 91.1% accuracy, 96.6% positive predictive value and 81.3% negative predictive value.

Conclusion

DWI and ADC map is a useful tool in differential diagnosis of malignant from benign liver lesions.     

Evaluation of a 32-channel versus a 12-channel head coil for high-resolution post-contrast MRI in giant cell arteritis (GCA) at 3 T

The aim of this study was to evaluate the diagnostic value of a 32-channel head coil for the characterization of mural inflammation patterns in the superficial cranial arteries in patients with giant cell arteritis (GCA) compared to a standard 12-channel coil at 3 T MRI.     

Development and evaluation of the Turkish matrix sentence test

Objectives: The Turkish matrix sentence test, TURMatrix, was developed for precise, internationally comparable speech intelligibility testing. Design: The TURMatrix comprises a base matrix of ten well-known Turkish names, numbers, adjectives, objects, verbs, from which syntactically fixed sentences were randomly composed. Test conduction may be in an open-set (standard), or closed-set response format. Homogeneity in intelligibility of the test material was optimized by applying level adaptations (maximal ± 3 dB) based on word-specific speech reception thresholds (SRTs). Test list equivalence was verified and reference values were determined. Study sample: Thirty-eight native listeners of Turkish with normal hearing. Results: After training, mean SRT and slope of the final test lists were ? 8.3 ± 0.2 dB SNR and 14.1 ± 1.0%/dB, respectively (fixed SNR measurements; inter-list variability). For adaptive measurements, average across listeners was ? 7.2 ± 0.7 dB SNR in the open-set and ? 7.9 ± 0.7 dB SNR in the closed-set response format. Mean SRT for adaptive measurements in the open-set response format in quiet was 20.3 ± 4.1 dB. Individual SRTs in quiet correlated more closely with audiograms than with SRTs in noise. Conclusions: The TURMatrix was developed according to European standards and provides reliable speech intelligibility measurements in noise and quiet.     

Advances of 3T MR imaging in visualizing trabecular bone structure of the calcaneus are partially SNR‐independent: Analysis using simulated noise in relation to micro‐CT, 1.5T MRI,and biomechanical strength

Purpose

To investigate differences in magnetic resonance imaging (MRI) of trabecular bone at 1.5T and 3.0T and to specifically study noise effects on the visualization and quantification of trabecular architecture using conventional histomorphometric and nonlinear measures of bone structure.

Materials and Methods

Sagittal MR images of 43 calcaneus specimens (donor age: 81 ± 10 years) were acquired at 1.5T and 3.0T using gradient echo sequences. Noise was added to obtain six sets of images with decreasing signal‐to‐noise ratios (SNRs). Micro‐CT images were obtained from biopsies taken from 37 calcaneus samples and bone strength was determined. Morphometric and nonlinear structure parameters were calculated in all datasets.

Results

Originally, SNR was 1.5 times higher at 3.0T. In the simulated image sets, SNR was similar at both fields. Trabecular dimensions measured by μCT were adequately estimated by MRI, with residual errors (e_r), ranging from 16% to 2.7% at 3.0T. Comparing e_r at similar SNR, 3.0T consistently displayed lower errors than 1.5T (eg, bone fraction at SNR ≈4: e_r[3.0T] = 15%; e_r[1.5T] = 21%, P < 0.05).

Conclusion

The advances of 3.0T compared to 1.5T in visualizing trabecular bone structure are partially SNR‐independent. The better performance at 3.0T may be explained by pronounced susceptibility, enhancing the visualization of thin trabecular structures. J. Magn. Reson. Imaging 2009;29:132–140. © 2008 Wiley‐Liss, Inc.