Ratio In Magnetic Resonance Imaging Research Articles

Implementing a two-stage, shim field-calibrated superconducting shimming method on a 7 T cryogen-free small animal MRI magnet

Ultrahigh field systems (≥ 7 T) can increase the signal-to-noise ratio of magnetic resonance imaging (MRI), improving imaging performance compared to systems with lower fields. However, these enhancements heavily rely on a high B0 magnetic field homogeneity level, which can be achieved through superconducting shimming. This paper presents a novel two-stage superconducting shimming method designed to achieve precise shimming for a 7 T MRI superconducting magnet. In the initial stage, detailed measurements and fittings were conducted to determine the current polarity and the axial or circumferential positions of the shim fields. Subsequently, an optimization strategy was implemented to determine the optimal shim currents with a flexible target field. The second stage involves an iterative process to fine-tune the current of a specific shim coil, identified as having the most significant impact on field homogeneity. The overall fitness of 99.5% underscores the precision in determining the current polarity and position of the shim fields. Significantly, the calibrated shim system substantially improves the peak-to-peak and Root Mean Square Error (RMSE) field homogeneities from 107.42 ppm and 37.00 ppm to 11.12 ppm and 3.26 ppm, respectively, representing improvements of 89.65% and 91.19%. Furthermore, the simulation results of the fine-tuning stage demonstrate additional enhancements in peak-to-peak field homogeneity, to 9.9 ppm by reducing the current of the Z2 shim coil by 51.3 mA. Additionally, the shimmed magnetic field exhibited high time stability, with a maximum variation of only 27 µT observed within 48 h. Thus, the proposed two-stage superconducting shimming framework effectively addresses the challenge of imperfect B0 magnetic fields, enhancing peak-to-peak and RMSE field homogeneity. The stepwise optimized approach also mitigates deviations caused by shim-to-shim coupling, demonstrating its efficacy in achieving precise shimming in ultrahigh-field MRI systems.

Feasibility and safety of contrast-enhanced magnetic resonance-guided adaptive radiotherapy for upper abdominal tumors: A preliminary exploration

This study investigates the use of contrast-enhanced magnetic resonance (MR) in MR-guided adaptive radiotherapy (MRgART) for upper abdominal tumors. Contrast-enhanced T1-weighted MR (cT1w MR) using half doses of gadoterate was used to guide daily adaptive radiotherapy for tumors poorly visualized without contrast. The use of gadoterate was found to be feasible and safe in 5-fraction MRgART and could improve the contrast-to-noise ratio of MR images. And the use of cT1w MR could reduce the interobserver variation of adaptive tumor delineation compared to plain T1w MR (4.41 vs. 6.58, p < 0.001) and T2w MR (4.41 vs. 7.42, p < 0.001).

Method for determining matching capacitances for floating cable traps in magnetic resonance imaging up to 14 T

Floating cable traps (FCTs) enhance coil tuning, improve the signal-to-noise ratio of magnetic resonance imaging (MRI), and reduce the risks to patients. As MRI technology continues to advance, it becomes crucial to design efficient FCTs that are tailored to different magnetic fields and nuclei. Here, a method is proposed for determining and correcting the appropriate capacitances for FCTs in MRI systems. To validate the effectiveness of this approach, FCTs were designed and manufactured for hydrogen nuclei in magnetic fields of 1.5–14 T. The results of bench testing show that the attenuation of common-mode currents was more than −20 dB, and the maximum frequency deviation in all the FCTs was 0.345%. Furthermore, the results of magnetic resonance spin-echo imaging show that the signal-to-noise ratio was improved significantly by using the FCTs. Overall, this study shows the effectiveness of the designed FCTs in improving signal-to-noise ratio, and it provides valuable insights for designing efficient FCTs tailored to different magnetic fields and nuclei in MRI applications.

Association between spinal cord compression ratio in magnetic resonance imaging, initial neurological status, and recovery after ventral slot in 57 dogs with cervical disc extrusion.

This retrospective, unblinded, single rater study evaluated images obtained from magnetic resonance imaging (MRI) of dogs with cervical intervertebral disc extrusion before being submitted to ventral slot decompression (VSD). Dogs were re-evaluated systematically at 10 and 30 days after VSD. The objectives of this study were to investigate the associations between the following parameters: (1) The maximal spinal cord compression ratio (SCCR) as seen on transverse MRI and pre-surgical neurological status (NS) grade; we hypothesized that dogs with greater SCCR will have worse pre-surgical NS grade at presentation; (2) Pre-surgical NS grade and postoperative recovery; we hypothesized that worse pre-surgical NS grade will be associated with longer postoperative recovery time; (3) SCCR and postoperative recovery; we hypothesized that dogs with higher SCCR will have longer recovery time; (4) Location of extrusion (cranial vs. caudal) and initial NS grade and outcomes; we hypothesized that caudal cervical extrusion will have worse NS grade and longer time to recovery; (5) Longitudinal extension of ventral CSF signal loss on HASTE pulse sequence and NS grade and time to recovery; we hypothesized that dogs with longer HASTE CSF attenuation will have higher NS grade and longer time to recovery. There was no significant association between SCCR and NS grade, suggesting that this relationship in the cervical region is similar to what is observed in the thoracolumbar region, rejecting our first hypothesis. There was a significant difference between ambulatory tetraparesis dogs versus non-ambulatory tetraparesis dogs regarding complete recovery at 10 days: dogs with NS grade 1, 2, or 3 overall recovered faster than dogs with NS grade 4. However, there was no significant difference between these groups regarding complete recovery at 30 days, thereby accepting our second hypothesis at 10 days and rejecting it at 30 days. There was no correlation between SCCR and recovery time, rejecting our third hypothesis. Caudal cervical extrusion did not show higher NS grade or longer recovery time than cranial extrusion, rejecting our fourth hypothesis. CSF attenuation length ratio on HASTE images was not significantly correlated with NS grade but weakly correlate with post-surgical recovery time, partially accepting our fifth hypothesis.

Seeking a Widely Adoptable Practical Standard to Estimate Signal-to-Noise Ratio in Magnetic Resonance Imaging for Multiple-Coil Reconstructions.

Signal-to-noise ratio (SNR) is used to evaluate the performance of magnetic resonance (MR) imaging systems. Accurate and consistent estimations are needed to routinely use SNR to assess coils and image reconstruction techniques. To identify a reliable and practical method for SNR estimation in multiple-coil reconstructions. Technical evaluation and comparison. A uniform phantom and four healthy volunteers: 35, 38, 39 y/o males, 25 y/o female. Two-dimensional multislice gradient-echo pulse sequence at 3 T and 7 T. Reference-standard SNR was calculated from 100 multiple replicas. Six SNR methods were compared against it: difference image (DI), analytic array combination (AC), pseudo-multiple-replica (PMR), generalized pseudo-replica (GPR), smoothed image subtraction (SIS), and DI with temporal instability correction (TIC). The assessment was repeated for different multiple-coil reconstructions. SNR methods were evaluated in terms of relative deviation (RD) and normalized mutual information (NMI) with respect to the reference-standard, using a linear regression (0.05 significance level) to assess how different factors affect accuracy. Average RD (phantom) for DI, AC, PMR, GPR, SIS, and TIC was 7.9%, 6%, 6.7%, 10.1%, 40%, and 14.6%, respectively. RD increased with acceleration. SNR maps with AC were the most similar to the reference standard (NMI=0.358). Considering all brain regions of interest, average RD for all SNR methods varied 96% among volunteers but remained approximately 10% for AC, PMR, and GPR, whereas it was more than 30% for DI, SIS, and TIC. RD was mainly affected by image reconstruction (beta=12) for AC and SNR entropy for SIS (beta=19). AC provided accurate and robust SNR estimation. PMR and GPR are more generally applicable than AC. DI and TIC should be used only at low acceleration factors, when an additional noise-only scan cannot be acquired. SIS is a single-acquisition alternative to DI for generalized autocalibrating partial parallel acquisition (GRAPPA) reconstructions. 1 TECHNICAL EFFICACY: Stage 1.

Frontispiece: On‐demand field shaping for enhanced magnetic resonance imaging using an ultrathin reconfigurable metasurface (View 3/2021)

In article number 20200099, Hanwei Wang and co-workers have proposed a theoritical design of an ultrathin reconfigurable metasurface to enhance the signal-to-noise ratio of magnetic resonance imaging. The enhancement can target a specific region in the imaging plane with any desired shapes while minimumly disrupt the spin-excitation to maintain a high imaging quality. In this cover, the spins pointing up illustrate the uniform excitation of protons of an imaging object. The different shapes of the component forming the metasurface create a strong coupling with the protons in a specific region, where the signals are selectively enhanced. The selected enhancement region in this cover is designed to form the shapes of “U” and “I” representing the University of Illinois.

A Review on MRI Denoising Methods

Many years ago, a lot of work has been done to enhance the resolution and signal-to-noise ratio of magnetic resonance images for accurate monitoring. However, artifacts and random noise still affects the quality of Magnetic Resonance images. In order to maintain the relevant image content, compensation between noise reduction and preservation of details have to be made. Therefore, noise reduction is a paramount challenge. A published literature review of each technique is discussed along with its advantages and limitations. After the introduction of magnetic resonance imaging (MRI) technology, the famous approaches for denoising MRI images are classified with overview of each method.

Receive Bandwidth Variation Effect Toward the Signal and Contrast to Noise Ratio in Magnetic Resonance Imaging (MRI) Cervical Examination with the Sequence of T1 Weighted Turbo Spin Echo

Introduction: The received bandwidth parameter is a parameter affecting the value of Signal to Noise Ratio (SNR) where the radiographer is usually stuck to the existing protocol: the bandwidth of 146 Hz /Px. In fact, by doing the variation of received bandwidth, the pictures of SNR variation will be obtained to define the best bandwidth to SNR and contrast to noise ratio (CNR). Objective: The purpose of this research is to find out the effect of received bandwidth variation on SNR and CNR and to determine the most optimal received bandwidth for SNR and CNR on cervical MRI with the sequence of T1 Weighted Turbo Spin Echo (TSE) in the sagittal slice. Methods: The type of this research is quantitative research with experimental approach done with MRI 1.5 Tesla at General Hospital Dr. Hasan Sadikin Bandung. The data were 35 cervical TRL images of TSE in the sagittal slice from 7 probands with 5 received bandwidth variations (106 Hz / Px, 126 Hz / Px, 146 Hz / Px, 166 Hz / Px and 186 Hz / Px). To obtain SNR and CNR values, an area of interest (ROI) measurement is performed on the corpus, discus, spinal cord and CSF regions to obtain the average signal and compared with the standard deviation value of the background. Data was analyzed with linear regression and descriptive mean rank test. Result: The result of the research shows the effect of received bandwidth on SNR and CNR on MRI cervical. There is a strong correlation between received bandwidth variation with cervical SNR with correlation coefficient = 0.639, and there is a moderate correlation between received bandwidth variation with CNR cervical with correlation coefficient = 0,532 with p - value < 0.05. The optimal received bandwidth value of the T1WI saturation T1WI T1WI MRI is 106 Hx / px with a mean rank of SNR = 160.5 and mean rank of CNR = 76.59. Conclusion: The received bandwidth variations on SNR and CNR in MRI significantly affect the cervical examination. The optimal received bandwidth value of T1WI TSE in the sagittal slice is 106 Hx / px.

A Study on the Size of Bore on Signal to Noise Ratio (SNR) in Magnetic Resonance Imaging (MRI)

Background/Objectives: An objective of this study is to analyze the size of bore on signal to noise ratio in magnetic resonance imaging. Methods/Statistical Analysis: During this process, the magnetic field also shows irregularity due to the environmental factors. Therefore in this study, magnetic field non-uniformity according to the bore size of MRI will be examined as well as the influence on the image through SNR measurement. Findings: Avanto with bigger bore size has shown higher SNR value, and especially, it has shown 6 times or greater difference in TSE(Turbo Spin Echo) technique. Improvements: It would be imperative to conduct a test with a small bore size and a uniform magnet when the MRI test failure rate is high due to claustrophobia.

A Riemannian Bayesian Framework for Estimating Diffusion Tensor Images

Diffusion tensor magnetic resonance imaging (DT-MRI) is a non-invasive imaging technique allowing to estimate the molecular self-diffusion tensors of water within surrounding tissue. Due to the low signal-to-noise ratio of magnetic resonance images, reconstructed tensor images usually require some sort of regularization in a post-processing step. Previous approaches are either suboptimal with respect to the reconstruction or regularization step. This paper presents a Bayesian approach for simultaneous reconstruction and regularization of DT-MR images that allows to resolve the disadvantages of previous approaches. To this end, estimation theoretical concepts are generalized to tensor valued images that are considered as Riemannian manifolds. Doing so allows us to derive a maximum a posteriori estimator of the tensor image that considers both the statistical characteristics of the Rician noise occurring in MR images as well as the nonlinear structure of tensor valued images. Experiments on synthetic data as well as real DT-MRI data validate the advantage of considering both statistical as well as geometrical characteristics of DT-MRI.

Abstract P6-01-18: 2-Hydroxyestrone is associated with breast density measured by mammography and fat:water ratio magnetic resonance imaging in women taking tamoxifen

Abstract Research Objectives and Rationale. Tamoxifen (TAM) use has been shown to reduce breast cancer recurrence with the benefit greater in patients who experience a TAM-associated decrease in percent mammographic density(PMD); findings that support PMD as a biomarker of response to TAM. PMD is a radiographic phenomenon of breast fibroglandular tissue that is associated with breast cancer risk. PMD is inversely associated with body mass index (BMI) and sparse data have shown a weak positive association with the sex hormone levels. Limited data exist evaluating the relationship between TAM, 2OHE1:16 a-OHE1 ratio (concentrations previously hypothesized to be associated with a reduced risk of breast cancer) and PBD. Methods. Using cross-sectional baseline breast density (BD) from an ongoing prevention trial of diindolylmethane (DIM) in 121 women receiving TAM, we evaluated BD in relation to circulating TAM metabolites [TAM, endoxifen, 4-OH TAM, ND TAM], estradiol (E2), sex hormone-binding globulin (SHBG) and urinary 2-OHE1 and 16α-OHE1. PMD was assessed by mammography (n=65; 54%) and also a novel, non-radiative, non-contrast magnetic resonance imaging-derived fat-water ratio (FWR-MRI) as the fat fraction (Fra)50 and 80 (n=53; 44%) developed for repeat BD assessment in short intervals. This is our first report that BD using digitized mammograms is correlated with FWR-MRI-derived measures designated Fra50 and Fra80; Spearman ρ = 0.90 and 0.86, respectively, p &amp;lt; 0.001. Results. As previously demonstrated, BMI was inversely correlated with all measures of BD. No association was shown between TAM and TAM metabolites and BD or urinary 2OHE1. Further, we found no relationship between circulating E2 or SHBG concentrations and BD. In contrast, urinary 2OHE1 levels were positively correlated with BD across all measures of density; 2OHE1 levels were most strongly correlated with BD measured by FW-MRI using Fra80 (Spearman ρFra80=0.483; p=0.001 compared to ρFra50 =0.431; p = 0.004 and ρPD=0.400; p=0.003). A significant, but weaker, correlation was observed for the 2OHE1:16OHE1 ratio and BD (ρ values 0.34-0.38). The magnitude of the relationship between 2OHE1 and BD was similar in pre and post-menopausal women despite lower PBD after menopause. Conclusions. Our results replicate earlier work from Maskarinec et al. wherein excreted 2OHE1 was an independent determinant of BD. These data challenge the hypothesis proposed by Yager and Liehr that higher urinary 2OHE1 to 16OHE1 ratio would be indicative of reduced hormone tumorigenesis. These results suggest a possible comparable binding affinity for the estrogen receptor that may modify endogenous steroid hormones and their effects on BD. Our findings strengthen the arguments favoring a better mechanistic understanding of BD, the biological determinants and their relationship to breast cancer. This is particularly timely given new mandates to provide BD measures to all women undergoing mammography and recent findings that while BD is associated with breast cancer risk high BD is not associated with greater breast cancer mortality. Citation Format: Cynthia A Thomson, Patricia A Thompson, Betsy C Wertheim, Denise Roe, Marilyn T Marron, John-Phillipe Galons, Matthew A Kupinski, Maria I Altbach, Gertraud Maskarinec, Alison Stopeck. 2-Hydroxyestrone is associated with breast density measured by mammography and fat:water ratio magnetic resonance imaging in women taking tamoxifen [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-01-18.

Magnetic resonance fetal right lung volumetry and its efficacy in predicting postnatal short‐term outcomes of congenital left‐sided diaphragmatic hernia

We aimed to investigate whether the ratio of magnetic resonance imaging (MRI)-measured right lung volume (RLV) to ultrasonography-estimated bodyweight (RLV/BW) and observed-to-expected (o/e) RLV are of diagnostic value in predicting postnatal outcomes of left congenital diaphragmatic hernia (CDH). We included 32 CDH patients and 34 control subjects. Manually outlined fetal right lung areas on MRI were multiplied by the slice thickness and added to determine the entire volume. The association between RLV and RLV/BW with gestational age in the controls was examined using regression analysis. RLV/BW and o/e RLV were compared between surviving and non-surviving neonates with CDH. The expected fetal RLV was derived using the formula RLV (mm(3)) = 1.717 × (gestational weeks)(2.82). In the controls, RLV/BW was nearly constant during the third trimester. The 27 survivors with CDH had a median RLV/BW of 10.7 and a median o/e RLV of 60.0, whereas the five non-surviving neonates had a median RLV/BW of 4.3 and a median o/e RLV of 22.6; the differences were statistically significant. Assessment of fetal lungs by MRI volumetry is reliable for clinical use. RLV/BW and o/e RLV are potential predictors of postnatal outcomes of left CDH.

Capacitive approach to restore decoupling between channels for four‐element MR coil array

Multichannel coil arrays are increasingly being used to improve signal-to-noise ratio in magnetic resonance imaging (MRI). The decoupling between coils is an important parameter in array design. Indeed coupling between elements affects the resonance frequency of each single coil and decreases its sensitivity. Many solutions have been developed to achieve decoupling between elements of the multichannel coil array. Presented is a capacitive solution to restore channel decoupling of a specific four-channel receiver coil array using common conductors. The principle of an effective decoupling was first demonstrated by circuit simulations of |S|-parameters. A receive-only four-channel coil array was design for rat head MRI. Experimental |S|-parameter measurements validated the proposed capacitive approach by restoring decoupling between elements and particularly between external loops.

Stacked Phased Array Coils for Increasing the Signal-to-Noise Ratio in Magnetic Resonance Imaging

A new concept of using a stacked phased coil array to increase the signal-to-circuit noise ratio (SCNR) in magnetic resonance imaging (MRI) is introduced. Unlike conventional phased coil arrays, the proposed stacked phased coil array is constructed by stacking the coil elements closely together in the vertical direction. Through a proper combination of the coil terminal voltages, the SCNR is shown to increase with the square root of the number of coil elements. A prototype two-element array is constructed and an experimental method is designed to determine the combiner coefficients in a simulated MRI electromagnetic field environment. The experimental results show that the mutual coupling effect among the array coils can be totally removed and the combiner output voltage increases with the number of coil elements. This demonstrates the feasibility of the proposed method.

Signal-to-noise ratio evaluation in resonant ring metamaterial lenses for MRI applications

In this paper, we present a method for the evaluation of the signal-to-noise ratio in magnetic resonance imaging (MRI) coils loaded with resonant ring metamaterial lenses, in the presence of a conducting phantom resembling human tissue. The method accounts for the effects of the discrete and finite structure of the metamaterial. Numerical computations are validated with experimental results, including laboratory measurements and MRI experiments.

Relation of MR T2 image signal intensity ratio of cervical spondylotic myelopathy with clinical manifestations and prognosis

To investigate whether the signal intensity ratio in magnetic resonance imaging (MRI) and clinical manifestations can reflect prognosis in patients with cervical compressive myelopathy. Seventy-three patients with cervical compressive myelopathy treated with anterior, posterior, or posterior-anterior united decompression underwent 1.5-T MRI before surgery. T2-weighted images (T2WI) of the sagittal signal intensity on the cervical severe compression cord were obtained, and the regions of interest (ROIs) were taken by 0.05 cm(2). T2-weighted MR images of sagittal normal cord signal on the cervical between C7-T1 disc levels were obtained, and the ROIs were taken by 0.3 cm(2). Signal value is measured by computer and the signal ratio between the regions of the 0.05 cm(2) and 0.3 cm(2) was calculated. If no intramedullary high signal intensity was noted on T2-weighted MR images, the ROIs were taken by 0.05 cm(2) of the severe compression cord. The 73 patients were divided into 3 groups: low, medium, and high signal ratio groups (Group 1, 2, and 3, n = 18, 32, and 23 respectively). The recovery rate and JOA score of Group 1 were significantly higher, the age and Babinski sign positive rate were significantly lower, and disease duration was shorter in Group 1 than in Groups 2 and 3 (F = 22.009, P < 0.001, F = 5.561, P = 0.006, F = 6.371, P = 0.003, chi(2) = 15.719, P < 0.001, and chi(2) = 13.952, P = 0.001). There was no significant differences in sex among these 3 groups (chi(2) = 1.898, P = 0.387). The patients with light or without intramedullary signal change on T2WI experience a good surgical outcome. However, the patients with increase of signal intensity ratio and the occurrence of pyramidal sign show a poor prognosis after surgery.

Wavelet-based de-noising algorithm for images acquired with parallel magnetic resonance imaging (MRI)

Wavelet-based de-noising has been shown to improve image signal-to-noise ratio in magnetic resonance imaging (MRI) while maintaining spatial resolution. Wavelet-based de-noising techniques typically implemented in MRI require that noise displays uniform spatial distribution. However, images acquired with parallel MRI have spatially varying noise levels. In this work, a new algorithm for filtering images with parallel MRI is presented. The proposed algorithm extracts the edges from the original image and then generates a noise map from the wavelet coefficients at finer scales. The noise map is zeroed at locations where edges have been detected and directional analysis is also used to calculate noise in regions of low-contrast edges that may not have been detected. The new methodology was applied on phantom and brain images and compared with other applicable de-noising techniques. The performance of the proposed algorithm was shown to be comparable with other techniques in central areas of the images, where noise levels are high. In addition, finer details and edges were maintained in peripheral areas, where noise levels are low. The proposed methodology is fully automated and can be applied on final reconstructed images without requiring sensitivity profiles or noise matrices of the receiver coils, therefore making it suitable for implementation in a clinical MRI setting.

Measuring the signal-to-noise ratio in magnetic resonance imaging: a caveat

The validity of the signal-to-noise ratio (SNR) as an objective quality measure for biomedical images has been the subject of a long-standing debate. Nevertheless, the SNR is the most popularly used measure both for assessing the quality of images and for evaluating the effectiveness of image enhancement and signal processing techniques. In this correspondence, we illustrate that under certain conditions the SNR can be changed by a nonlinear transformation, and also that it is often hard to measure objectively. Therefore, the issue is not only how well the SNR correlates with image quality as perceived by a human observer (which has been the primary subject of earlier debate), but also that SNR is questionable from a quantitative measurement point of view.

Evaluation of iron overload by single voxel MRS measurement of liver T2.

To overcome the difficulty of poor signal-to-noise ratio of magnetic resonance imaging (MRI) in evaluating heavy iron overload by using a single voxel magnetic resonance spectroscopy (MRS) technique. A single voxel STEAM pulse sequence with a minimum TE of 1.5 msec and a sampling volume of 36.6 cm(3) was developed and applied to 1/T2 measurement of the liver in 14 patients with thalassemia whose liver iron concentration was determined through biopsy. The iron level ranged from 0.23 to 37.15 mg Fe/g dry tissue with a median value of 18.06. In all cases, strong MR signals were obtained. 1/T2 was strongly correlated with the liver iron concentration (r = 0.95, P < 0.00005). The single voxel MRS measurement of T2 in liver iron overload overcomes the difficulty of lack of detectable signals in conventional MRI when the iron level is high. There is an excellent correlation between the iron level and 1/T2.

Use of Dual Fresnel Transform Pairs to Improve Signal-to-Noise Ratio in Magnetic Resonance Imaging

Use of Dual Fresnel Transform Pairs to Improve Signal-to-Noise Ratio in Magnetic Resonance Imaging