Spoiled Gradient Recalled Echo Images Research Articles

Exploring the cognitive assessment potential of MRI-based volumetric hippocampal segmentation in Parkinson's disease.

To investigate the potential of magnetic resonance imaging (MRI)-based total and segmental hippocampus volume analysis in the assessment of cognitive status in Parkinson's disease (PD). We divided participants into three groups Group A-Parkinson patients (Pp) with normal cognitive status (n=25), Group B-Pp with dementia (n=17), and Group C-healthy controls (n=37). Three-dimensional T1W Fast Spoiled Gradient Recalled Echo images were used for Volbrain hippocampus subfield segmentation. We used the "Winterburn" protocol, which divides the hippocampus into five segments, Cornu Ammonis (CA),CA2/CA3, CA4/dentate gyrus, stratum radiatum, lacunosum, and moleculare, and subiculum. A total of 79 participants were included in the study, consisting of 42 individuals with PD (64.2% male) and 37 healthy controls (54.1% male). The mean age of PD was 60.9±10.7 years and the mean age of control group was 59.27±12.3 years. Significant differences were found in total hippocampal volumes between Group A and B (p=.047. Statistically significant group differences were found in total, right, and left CA1 volumes (analysis of variance [ANOVA]: F(2,76)=8.098, p=.001; F(2,76)=7.628, p=.001; F(2,76)=5.084, p=.008, respectively), as well as in total subiculum volumes (ANOVA: F(2,76)=4.368, p=.016). Post hoc tests showed that total subiculum volume was significantly lower in individuals with normal cognitive status (0.474±0.116cm3) compared to healthy controls (0.578±0.151cm3, p=.013). Volumetric hippocampal MRI can be used to assess the cognitive status of Pp. Longitudinal studies that evaluate Pp who progress from normal cognition to dementia are required to establish a causal relationship.

Implementation of Oxygen Enhanced Magnetic Resonance Imaging (OE-MRI) and a Pilot Genomic Study of Hypoxia in Bladder Cancer Xenografts.

Patients with hypoxic bladder cancer benefit from hypoxia modification added to radiotherapy, but no biomarkers exist to identify patients with hypoxic tumours. We, herein, aimed to implement oxygen-enhanced MRI (OE-MRI) in xenografts derived from muscle-invasive bladder cancer (MIBC) for future hypoxia biomarker discovery work; and generate gene expression data for future biomarker discovery. The flanks of female CD-1 nude mice inoculated with HT1376 MIBC cells. Mice with small (300 mm3) or large (700 mm3) tumours were imaged, breathing air then 100% O2, 1 h post injection with pimonidazole in an Agilant 7T 16cm bore magnet interfaced to a Bruker Avance III console with a T2-TurboRARE sequence using a dynamic MPRAGE acquisition. Dynamic Spoiled Gradient Recalled Echo images were acquired for 5 min, with 0.1mmol/kg Gd-DOTA (Dotarem, Guerbet, UK) injected after 60 s (1 ml/min). Voxel size and field of view of dynamic contrast enhanced (DCE)-MRI and OE-MRI scans were matched. The voxels considered as perfused with significant post-contrast enhancement (p<0.05) in DCE-MRI scans and tissue were further split into pOxyE (normoxic) and pOxyR (hypoxic) regions. Tumours harvested in liquid N2, sectioned, RNA was extracted and transcriptomes analysed using Clariom S microarrays. Imaged hypoxic regions were greater in the larger versus smaller tumour. Expression of known hypoxia-inducible genes and a 24 gene bladder cancer hypoxia score were higher in pimonidazole-high versus -low regions: CA9 (p=0.012) and SLC2A1 (p=0.012) demonstrating expected transcriptomic behaviour. OE-MRI was successfully implemented in MIBC-derived xenografts. Transcriptomic data derived from hypoxic and non-hypoxic xenograft regions will be useful for future studies.

Functional and Morphological Brain Alterations in Dysthyroid Optic Neuropathy: A Combined Resting-State fMRI and Voxel-Based Morphometry Study.

Increasing evidence has indicated that the entire visual pathway from retina to visual cortex may be involved in dysthyroid optic neuropathy (DON) pathological mechanisms. To explore the functional and morphological brain characteristics in DON and their relationship with ophthalmologic performance. Retrospective. A total of 30 DON patients, 40 thyroid-associated ophthalmopathy (TAO) without DON patients and 21 healthy-controls (HCs). A 3.0 T, 3D T1-weighted spoiled gradient-recalled echo and gradient-recalled echo-planar imaging. Functional and structural alterations in brain regions were evaluated with fractional amplitude of low-frequency fluctuations, degree centrality (DC), and gray matter volume (GMV). Clinical activity score (CAS) is assessed across patients. One-way analysis of variance with post hoc two sample t-tests (GRF-corrected, voxel level: P< 0.005, cluster level: P< 0.05) and correlation analysis (significance level: P< 0.05). Compared to HCs, DON patients had significantly decreased DC values in the bilateral BA17 and BA18 regions. Compared to the TAO group, DON patients had decreased GMV in the left anterior cingulate cortex, left middle frontal gyrus, left lingual gyrus, left parietal gyrus, right Rolandic operculum, left supplementary motor area, and right middle temporal gyrus. In addition, GMV in the right Rolandic operculum was significantly positively correlated with CAS (correlation coefficient: r= 0.448). This study showed significant morphological and functional alterations in visual cortex and morphological alterations in partial default mode network regions of DON patients, which may provide insights into the mechanism of vision loss and may facilitate the diagnosis and treatment of DON. 3. Stage 3.

T1 mapping as a surrogate marker of chemotherapy response evaluation in patients with osteosarcoma

ObjectivesTo characterize baseline T1 values of tumors, measure changes after the course of chemotherapy, and evaluate its potential as a marker of response assessment in patients with osteosarcoma. Materials and MethodsA total of 35 patients (male:female = 27:8; age = 17.9 ± 6 years; metastatic:localized = 11:24) with biopsy-proven osteosarcoma were analyzed prospectively. All patients underwent magnetic resonance imaging before neoadjuvant chemotherapy (NACT) (baseline) and after NACT completion (follow-up), followed by surgery and histopathological evaluation. Histopathological necrosis served as the gold standard for assessing chemotherapy response (responder: ≥50% necrosis and non-responder: <50% necrosis). Three-dimensional spoiled gradient recalled echo images were acquired with varying flip angles (50, 100, 200, and 300) using a 1.5 Tesla scanner. T1 values were estimated in healthy muscle tissue and tumors at baseline and follow-up, and the relative percentage changes after NACT (ΔT1) were evaluated, and histogram analysis was performed to characterize the T1 value of the tumor and predict the NACT response using the Pearson correlation coefficient (r) and receiver operating characteristic curve analysis. ResultsAt baseline, a significantly higher T1-mean (830.96 ± 193.88 msec versus 683.29 ± 210.00 msec; p = 0.003) and lower T1-skewness (0.86 ± 1.66 versus 1.60 ± 1.55; p = 0.02) were observed in osteosarcoma than healthy tissue. Responder:non-responder ratio was 13:22. At baseline, a significantly higher T1-mean (936.14 ± 193.17 msec versus 768.82 ± 169.25 msec; p = 0.018) and lower T1-skewness (-0.17 ± 0.85 versus 1.47 ± 1.73; p = 0.003) were observed among responders, than non-responders. After NACT, ΔT1 in tumor was significantly higher among responders than non-responders (-27.22 ± 12.17% versus −15.70 ± 18.99%; p = 0.034). ΔT1-mean and ΔT1-skewness after NACT were moderately correlated (r = − 0.4, p = 0.030; r = 0.4, p = 0.011) with histopathological necrosis. For predicting NACT response, T1-mean and T1-skewness jointly produced an area under the curve (AUC) = 0.80 at baseline, and ΔT1-mean and ΔT1-skewness jointly produced AUC = 0.76 after NACT. ConclusionThe mean and skewness of T1 values in osteosarcoma are potential non-invasive imaging markers for chemotherapy response assessment.

Quantitative analysis of the ACL and PCL using T1rho and T2 relaxation time mapping: an exploratory, cross-sectional comparison between OA and healthy control knees

BackgroundQuantitative magnetic resonance imaging (MRI) methods such as T1rho and T2 mapping are sensitive to changes in tissue composition, however their use in cruciate ligament assessment has been limited to studies of asymptomatic populations or patients with posterior cruciate ligament tears only. The aim of this preliminary study was to compare T1rho and T2 relaxation times of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) between subjects with mild-to-moderate knee osteoarthritis (OA) and healthy controls.MethodsA single knee of 15 patients with mild-to-moderate knee OA (Kellgren-Lawrence grades 2–3) and of 6 age-matched controls was imaged using a 3.0 T MRI. Three-dimensional (3D) fat-saturated spoiled gradient recalled-echo images were acquired for morphological assessment and T1ρ- and T2-prepared pseudo-steady-state 3D fast spin echo images for compositional assessment of the cruciate ligaments. Manual segmentation of whole ACL and PCL, as well as proximal / middle / distal thirds of both ligaments was carried out by two readers using ITK-SNAP and mean relaxation times were recorded. Variation between thirds of the ligament were assessed using repeated measures ANOVAs and differences in these variations between groups using a Kruskal-Wallis test. Inter- and intra-rater reliability were assessed using intraclass correlation coefficients (ICCs).ResultsIn OA knees, both T1rho and T2 values were significantly higher in the distal ACL when compared to the rest of the ligament with the greatest differences in T1rho (e.g. distal mean = 54.5 ms, proximal = 47.0 ms, p < 0.001). The variation of T2 values within the PCL was lower in OA knees (OA: distal vs middle vs proximal mean = 28.5 ms vs 29.1 ms vs 28.7 ms, p = 0.748; Control: distal vs middle vs proximal mean = 26.4 ms vs 32.7 ms vs 33.3 ms, p = 0.009). ICCs were excellent for the majority of variables.ConclusionT1rho and T2 mapping of the cruciate ligaments is feasible and reliable. Changes within ligaments associated with OA may not be homogeneous. This study is an important step forward in developing a non-invasive, radiological biomarker to assess the ligaments in diseased human populations in-vivo.

Four-angle method for practical ultra-high-resolution magnetic resonance mapping of brain longitudinal relaxation time and apparent proton density

Changes in longitudinal relaxation time (T1) and proton density (PD) are sensitive indicators of microstructural alterations associated with various central nervous system diseases as well as brain maturation and aging. In this work, we introduce a new approach for rapid and accurate high-resolution (HR) or ultra HR (UHR) mapping of T1 and apparent PD (APD) of the brain with correction of radiofrequency field, B1, inhomogeneities. The four-angle method (FAM) uses four spoiled-gradient recalled-echo (SPGR) images acquired at different flip angles (FA) and short repetition times (TRs). The first two SPGR images are acquired at low-spatial resolution and used to accurately map the active B1+ field with the recently introduced steady-state double angle method (SS-DAM). The estimated B1+ map is used in conjunction with the two other SPGR images, acquired at HR or UHR, to map T1 and APD. The method is evaluated with numerical, phantom, and in-vivo imaging measurements. Furthermore, we investigated imaging acceleration methods to further shorten the acquisition time. Our results indicate that FAM provides an accurate method for simultaneous HR or UHR mapping of T1 and APD in human brain in clinical high-field MRI. Derived parameter maps without B1+correction suffer from large inaccuracies, but this issue is well-corrected through use of the SS-DAM. Furthermore, the use of SPGR imaging with short TR and phased-array coil acquisition permits substantial imaging acceleration and enables robust HR or UHR T1 and APD mapping in a clinically acceptable time frame, with whole brain coverage obtained in less than 2 min or 5 min, respectively. The method exhibits high reproducibility and benefits from the use of the conventional SPGR sequence, available in all preclinical and clinical MRI machines, and very simple modeling to address a critical outstanding issue in neuroimaging.

Steady-state double-angle method for rapid B1 mapping.

To introduce an accurate, rapid, and practical method for active B1 field mapping based on the double-angle method (DAM) in the steady-state (SS) signal regime. We introduced and evaluated the performance of the SS-DAM approach to map the B1 field and compared the results to those calculated from the conventional DAM approach. Similar to DAM, SS-DAM uses the signal intensity ratio of 2 magnitude images acquired with different flip angles using the spoiled gradient recalled echo sequence. However, unlike DAM, in SS-DAM, these 2 spoiled gradient recalled echo images are acquired with very short TR, which allows substantially reduced acquisition time. Numerical, phantom, and in vivo brain imaging analyses, representing a wide range of T1 s and large B1 variation, were conducted. Methods for further accelerating acquisition were also investigated. Our results demonstrate the potential of the SS-DAM approach to be applied widely in the clinical setting. B1 maps derived from SS-DAM were demonstrated to be quantitatively comparable to those derived from DAM but were derived much more rapidly. Large-volume B1 maps were obtained at a field strength of 3 tesla within clinically acceptable acquisition times. SS-DAM permits accurate B1 mapping in the clinical setting, with whole-brain coverage in less than 1 min.

Technical report: gadoxetate-disodium-enhanced 2D R2* mapping: a novel approach for assessing bile ducts in living donors.

Gadoxetate-disodium (Gd-EOB-DTPA)-enhanced 3D T1- weighted (T1w) MR cholangiography (MRC) is an efficient method to evaluate biliary anatomy due to T1 shortening of excreted contrast in the bile. A method that exploits both T1 shortening and T2* effects may produce even greater bile duct conspicuity. The aim of our study is to determine feasibility and compare the diagnostic performance of two-dimensional (2D) T1w multi-echo (ME) spoiled gradient-recalled-echo (SPGR) derived R2* maps against T1w MRC for bile duct visualization in living liver donor candidates. Ten potential living liver donor candidates underwent pretransplant 3T MRI and were included in our study. Following injection of Gd-EOBDTPA and a 20-min delay, 3D T1w MRC and 2D T1w ME SPGR images were acquired. 2D R2* maps were generated inline by the scanner assuming exponential decay. The 3D T1w MRC and 2D R2* maps were retrospectively and independently reviewed in two separate sessions by three radiologists. Visualization of eight bile duct segments was scored using a 4-point ordinal scale. The scores were compared using mixed effects regression model. Imaging was tolerated by all donors and R2* maps were successfully generated in all cases. Visualization scores of 2D R2* maps were significantly higher than 3D T1w MRC for right anterior (p=0.003) and posterior (p=0.0001), segment 2 (p<0.0001), segment 3 (p=0.0001), and segment 4 (p<0.0001) ducts. Gd-EOB-DTPA-enhanced 2D R2* mapping is a feasible method for evaluating the bile ducts in living donors and may be a valuable addition to the living liver donor MR protocol for delineating intrahepatic biliary anatomy.

Evaluation of a respiratory navigator-gating technique in Gd-EOB-DTPA-enhanced magnetic resonance imaging for the assessment of liver tumors

ObjectivesWe investigated the clinical usefulness of respiratory navigator-gating technique for the assessment of liver tumors in Gd-EOB-DTPA-enhanced magnetic resonance (MR) imaging. MethodsEighty patients who underwent Gd-EOB-DTPA-enhanced MR imaging to evaluate known or suspected liver tumors were enrolled. Three-dimensional spoiled gradient-recalled echo images of the liver were acquired in the hepatobiliary phase by the following three methods: breath-hold imaging, navigator-gated low-resolution imaging, and navigator-gated high-resolution imaging. Navigator-gated imaging was performed during free breathing. Spatial resolution was identical between breath-hold imaging and gated low-resolution imaging. Signal intensities in the liver, muscle, and spleen were measured in 20 patients. Image quality was visually evaluated in all 80 patients. The detection rate and lesion conspicuity were assessed for 71 malignant liver lesions identified in 29 patients. ResultsThe liver-to-muscle and liver-to-spleen signal ratios were significantly lower for gated images compared to breath-hold images. Images of acceptable quality were obtained in most patients by all three methods, and the overall image quality of axial images did not differ significantly among the imaging methods, although superior reformatted coronal images were obtained by gated high-resolution imaging. The detection rates of malignant liver lesions were similar among the three imaging methods, although lesion conspicuity was significantly better for breath-hold imaging compared to gated imaging. ConclusionsNavigator-gated imaging provided image qualities and detection rates of malignant liver lesions comparable to breath-hold imaging in Gd-EOB-DTPA-enhanced MR imaging; however, no additional benefits of high-resolution imaging were proven for lesion evaluation.

Motion detection improvement of a pencil-beam navigator echo using a gradient reversal technique

PurposeTo develop and demonstrate the feasibility of a pencil-beam navigator using a gradient reversal technique for reducing signal contamination from undesired excitation for precise motion detection and correction. Materials and methodsThe navigator echo was obtained using normal and reversed gradient waveforms sequentially in three-dimensional spoiled gradient-recalled echo imaging. These two signals were combined in the complex domain for generating the final navigator data, which were used for detecting the diaphragm motion to nullify the side lobe effects with the smallest radius from the beam center. The navigator signals were compared with and without the proposed technique in phantom and human scans. In addition, navigator-gated imaging was performed in the human scans. ResultsIn a phantom experiment, the proposed technique diminished signals from a phantom placed outside the beam’s area. In human scans, the proposed technique reduced undesired signals in the navigator data for all subjects. The resultant images had fewer motion-induced ghosts than the images from the conventional technique for 8 subjects out of 10. ConclusionsWe have demonstrated that the gradient reversal technique reduced undesired signals in a pencil-beam navigator. This technique can be an alternative for free-breathing abdominal scan when the conventional navigator technique cannot detect the patient’s respiratory motion precisely.

Optimal techniques for magnetic resonance imaging of the liver using a respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence

PurposeTo optimize the navigator-gating technique for the acquisition of high-quality three-dimensional spoiled gradient-recalled echo (3D SPGR) images of the liver during free breathing. Materials and methodsTen healthy volunteers underwent 3D SPGR magnetic resonance imaging of the liver using a conventional navigator-gated 3D SPGR (cNAV-3D-SPGR) sequence or an enhanced navigator-gated 3D SPGR (eNAV-3D-SPGR) sequence. No exogenous contrast agent was used. A 20-ms wait period was inserted between the 3D SPGR acquisition component and navigator component of the eNAV-3D-SPGR sequence to allow T1 recovery. Visual evaluation and calculation of the signal-to-noise ratio were performed to compare image quality between the imaging techniques. ResultThe eNAV-3D-SPGR sequence provided better noise properties than the cNAV-3D-SPGR sequence visually and quantitatively. Navigator gating with an acceptance window of 2mm effectively inhibited respiratory motion artifacts. The widening of the window to 6mm shortened the acquisition time but increased motion artifacts, resulting in degradation of overall image quality. Neither slice tracking nor incorporation of short breath holding successfully compensated for the widening of the window. ConclusionThe eNAV-3D-SPGR sequence with an acceptance window of 2mm provides high-quality 3D SPGR images of the liver.

T₁ mapping using variable flip angle SPGR data with flip angle correction.

To improve the calculation of T1 relaxation time from a set of variable flip-angle (FA) spoiled gradient recalled echo images. The proposed method: (a) uses a uniform weighting of all FAs, (b) takes into account global inaccuracies in the generation of the prescribed FAs by estimating the actual FAs, and (c) incorporates data-driven local B1 inhomogeneity corrections. The method was validated and its accuracy tested using simulated data, phantom, and in vivo experiments. Results were compared with existing analysis methods and to inversion recovery (IR). Consistency was assessed by means of repeated scans of two subjects. Reference values were obtained from eight healthy subjects from various brain regions and compared with literature values. The method accurately and consistently estimated T1 values in all cases. The method was more robust, in comparison with the standard method, to the choice of FA set; to inaccuracies in generation of the prescribed FAs (in simulated data, T1 estimation error was 12.1 ms versus 235.5 ms); demonstrated greater consistency (in vivo study showed interscan T1 difference of 80 ms versus 356 ms); and achieved a better agreement with IR on phantom (median absolute difference of 123.8 ms versus 790 ms). Reference T1 values were 883/801 ms for female/male in white matter and 1501/1349 ms in gray matter, within the range previously reported. The proposed method overcomes some inaccuracies in FA production, providing more accurate estimation of T1 values compared with standard methods, and is applicable for currently available data.

Brain Expansion in Patients With Type II Diabetes Following Insulin Therapy: A Preliminary Study With Longitudinal Voxel‐Based Morphometry

We performed a longitudinal analysis based on magnetic resonance (MR) imaging to investigate the brain structural and perfusion changes caused by insulin therapy in patients with type II diabetes. High resolution three-dimensional T1-weighted fast spoiled gradient recalled echo images and flow-sensitive alternating inversion recovery (FAIR) images were obtained from 11 patients with type II diabetes before and 1 year after initiation of insulin therapy and 11 normal controls. Brain volume changes were investigated by a longitudinal voxel-based morphometry (VBM), and perfusion changes were evaluated by FAIR imaging between baseline and follow-up data. Significant regional gray matter (GM) expansion located in bilateral frontal, parietal, and left occipital lobes, and regional white matter (WM) expansion was shown in left precentral subcortical WM and right angular subcortical WM after insulin therapy (P < .05 with FDR correction). Brain hyperperfusion was detected in bilateral frontal cortex, left occipital cortex, and right temporal cortex after insulin therapy (P < .05). In patients with type II diabetes, brain expansion and hyperperfusion were demonstrated 1 year after initiation of insulin therapy, and insulin therapy could contribute to the brain volume gainment in the patients with type II diabetes.

Usefulness of three-dimensional T1-weighted spoiled gradient-recalled echo and three-dimensional heavily T2-weighted images in preoperative evaluation of spinal dysraphism

The aim of this study was to evaluate the usefulness of three-dimensional T1-weighted spoiled gradient-recalled echo (3D T1-GRE) images for the preoperative anatomical evaluation of lumbosacral lipoma, thick filum terminale, and myelomeningocele as a means of compensating for the drawbacks of 3D heavily T2-weighted (3D hT2-W) images. Nine patients with lumbosacral lipomas, one patient with tight filum terminale, and five patients with myelomeningoceles were included in this study. 3D T1-GRE images were compared with 3D hT2-W images or conventional magnetic resonance images in terms of delineation of lipomas and other structures in the patients with lipomas and tight filum terminale. For patients with myelomeningoceles, 3D T1-GRE images were compared with 3D hT2-W images in terms of artifacts in the cerebrospinal fluid (CSF) space. The 3D T1-GRE images demonstrated lipomas with good contrast to the spinal cord and CSF space and more clearly delineated the anatomical relationship between lipomas and these structures than did the 3D hT2-W images. The 3D T1-GRE images delineated dural defects through which extradural lipomas penetrated into the intradural space. The 3D T1-GRE images also demonstrated the presence or absence of lipomas in the filum terminale and the absence of artifact in the myelomeningoceles. Furthermore, they were useful for differentiating artifacts observed on the 3D hT2-W images from nerve elements. The complementary use of 3D T1-GRE and 3D hT2-W images may compensate for the drawbacks of 3D hT2-W images and may eventually improve lesion visualization and surgical decision making.

Utility of gadolinium-enhanced MR urography in detection of bladder carcinoma

ObjectivesTo evaluate the diagnostic accuracy of MR urography (MRU) in detecting bladder carcinoma. MethodsA retrospective review of 107 MRU exams obtained to evaluate for possible upper urinary tract urothelial carcinoma from 5/2005 to 5/2009 was performed by two experienced abdominal radiologists. Interpretation of the presence or absence of bladder carcinoma and lesion conspicuity in each imaging phase was made using 5-point confidence grading scales. Exams included 3D T1-weighted spoiled gradient-recalled echo images through the kidneys, ureters and bladder in the coronal plane during parenchymal phases and in both coronal and axial planes during pyelographic phases after intravenous administration of gadolinium and furosemide. Standard of reference was cystoscopy or cystectomy within 30 days of MRU. Statistical measures of performance, including receiver operating characteristics area under the curve (Az) values were calculated. ResultsBladder carcinoma was present in 26/107 patients (24%). Sensitivity, specificity, accuracy, positive predictive value, negative predictive value and Az value were 73.1%, 91.4%, 86.9%, 73.1%, 91.4%, 0.89 for the first reviewer, and 84.6%, 75.3%, 77.6%, 52.4%, 93.8%, 0.86 for the second. Lesion conspicuity was superior on the parenchymal phase compared to the pyelographic phase (p=0.04). ConclusionsMRU obtained for suspicion of upper urinary tract TCC has a moderate accuracy in detecting bladder carcinoma.

Cross-sectional investigation of correlation between hepatic steatosis and IVIM perfusion on MR imaging

The purpose of this study was to investigate the relationship between liver fat fraction (FF) and diffusion parameters derived from the intravoxel incoherent motion (IVIM) model. Thirty-six subjects with suspected nonalcoholic fatty liver disease underwent diffusion-weighted magnetic resonance imaging with 10 b-values and spoiled gradient recalled echo imaging with six echoes for fat quantification. Correlations were measured between FF, transverse relaxivity (R2⁎), diffusivity (D) and perfusion fraction (f). The primary finding was that no significant correlation was obtained for D vs. FF or f vs. FF. Significant correlations were obtained for D vs. R2⁎ (r=−0.490, P=.002) and f vs. D (r=−0.458, P=.005). The conclusion is that hepatic steatosis does not affect measurement of perfusion or diffusion and therefore is unlikely to confound the use of apparent diffusivity to evaluate hepatic fibrosis.

TROMBONE: T1-relaxation-oblivious mapping of transmit radio-frequency field (B1) for MRI at high magnetic fields.

Fast, 3D radio-frequency transmit field (B1) mapping is important for parallel transmission, spatially selective pulse design and quantitative MRI applications. It has been shown that actual flip angle imaging--two interleaved spoiled gradient recalled echo images acquired in steady state with two very short time delays (TR1, TR2)--is an attractive method of B1 mapping. Herein, we describe the TROMBONE method that efficiently integrates actual flip angle imaging with EPI imaging, alleviates very short TR requirement of actual flip angle imaging and through their synergy yields up to 16 times higher precision in B1 estimation in the same experimental time. High precision of TROMBONE can be traded for faster scans. The map of B1 reconstructed from the ratio of intensities of two images is insensitive to longitudinal relaxation time (T1) in the physiologically relevant range. A table of the optimal acquisition protocol parameters for various target experimental conditions is provided.

Gadolinium Enhanced Magnetic Resonance Urography for Upper Urinary Tract Malignancy

We retrospectively evaluated the accuracy of gadolinium enhanced magnetic resonance urography to detect upper urinary tract tumors. A total of 91 magnetic resonance urography studies for suspected upper tract malignancy were done in 70 males and 18 females with a mean age of 71.7 years. Breath hold coronal T2-weighted single shot fast spin-echo and breath-hold coronal 3-dimensional T1-weighted spoiled gradient-recalled echo images with fat suppression were obtained during the nephrographic and excretory phases after intravenous injection of gadolinium based contrast material. Two radiologists independently reviewed magnetic resonance images for a tumor by 4 regions (right/left and renal collecting system/ureter). Sensitivity, specificity and accuracy were calculated. A total of 35 urinary tract regions in 18 males and 7 females with a mean age of 70.4 years were confirmed to have an upper tract malignant tumor and 219 urinary tract regions were confirmed to be tumor-free. Sensitivity, specificity and accuracy to detect upper urinary tract malignancy were 74.3%, 96.8% and 93.7% for reviewer 1, and 62.9%, 96.3% and 91.7% for reviewer 2, respectively. When patients with a ureteral stent or nephrostomy tube were excluded from analysis, sensitivity, specificity and accuracy were 86.2%, 99.5% and 97.7% for reviewer 1, and 72.4%, 97.9% and 94.6% for reviewer 2, respectively. Gadolinium enhanced magnetic resonance urography is accurate to detect upper urinary tract malignant tumors.

Intensity correction with a pair of spoiled gradient recalled echo images

Intensity inhomogeneities in magnetic resonance images (MRI) are a frequently occurring artefact, and result in the same tissue class to have vastly different intensities within an image. These inhomogeneities can be modelled by a slowly varying field, which is also called the bias field. Previous phantom-, image- or sequence based approaches suffer from long scan times, post-processing times or do not sufficiently remove the intensity variations. These intensity variations cause problems for quantitative image analysis algorithms (segmentation, registration) as well as clinicians (e.g. by complicating the visual assessment). This paper presents a novel technique (COIN, correction of intensity inhomogeneities) that uses two calibration images (fast spoiled gradient echo) to map a parameter containing the bias field, which is specific to the patient during a particular exam. This parametric map can then be used to correct any other images acquired during the same exam, regardless of the sequence employed. By using a short repetition time (less than 5 ms) for the calibration scans, the additional scan time is reduced to 60 s (max). The subsequent post-processing time is approximately 60 s per 20 slices. We successfully validate our approach on simulated brain MRI as well as real liver and spinal images. These images were acquired with a number of different coils, sequences and weightings. A comparison of our method with an existing, commercially available algorithm by radiologists shows that COIN is superior.

Linear least‐squares method for unbiased estimation of T1 from SPGR signals

The longitudinal relaxation time, T(1), can be estimated from two or more spoiled gradient recalled echo images (SPGR) acquired with different flip angles and/or repetition times (TRs). The function relating signal intensity to flip angle and TR is nonlinear; however, a linear form proposed 30 years ago is currently widely used. Here we show that this linear method provides T(1) estimates that have similar precision but lower accuracy than those obtained with a nonlinear method. We also show that T(1) estimated by the linear method is biased due to improper accounting for noise in the fitting. This bias can be significant for clinical SPGR images; for example, T(1) estimated in brain tissue (800 ms < T(1) < 1600 ms) can be overestimated by 10% to 20%. We propose a weighting scheme that correctly accounts for the noise contribution in the fitting procedure. Monte Carlo simulations of SPGR experiments are used to evaluate the accuracy of the estimated T(1) from the widely-used linear, the proposed weighted-uncertainty linear, and the nonlinear methods. We show that the linear method with weighted uncertainties reduces the bias of the linear method, providing T(1) estimates comparable in precision and accuracy to those of the nonlinear method while reducing computation time significantly.