Variable TR Research Articles

Assessment of cerebral perfusion in moyamoya disease with dynamic pseudo-continuous arterial spin labeling using a variable repetition time scheme with optimized background suppression.

Accurate assessment of cerebral perfusion in moyamoya disease is necessary to determine the indication for treatment. We aimed to investigate the usefulness of dynamic PCASL using a variable TR scheme with optimized background suppression in the evaluation of cerebral perfusion in moyamoya disease. We retrospectively analyzed the images of 24 patients (6 men and 18 women, mean age 31.4 ± 18.2years) with moyamoya disease; each of whom was imaged with both dynamic PCASL using the variable-TR scheme and 123IMP SPECT with acetazolamide challenge. ASL dynamic data at 10 phases are acquired by changing the LD and PLD. The background suppression timing was optimized for each phase. CBF and ATT were measured with ASL, and CBF and CVR to an acetazolamide challenge were measured with SPECT. A significant moderate correlation was found between the CBF measured by dynamic PCASL and that by SPECT (r = 0.53, P < 0.001). The CBF measured by dynamic PCASL (52.5 ± 13.3ml/100mg/min) was significantly higher than that measured by SPECT (43.0 ± 12.6ml/100mg/min, P < 0.001). The ATT measured by dynamic PCASL showed a significant correlation with the CVR measured by SPECT (r = 0.44, P < 0.001). ATT was significantly longer in areas where the CVR was impaired (CVR < 18.4%, ATT = 1812 ± 353ms) than in areas where it was preserved (CVR > 18.4%, ATT = 1301 ± 437ms, P < 0.001). The ROC analysis showed a moderate accuracy (AUC = 0.807, sensitivity = 87.7%, specificity = 70.4%) when the cutoff value of ATT was set at 1518ms. Dynamic PCASL using this scheme was found to be useful for assessing cerebral perfusion in moyamoya disease.

Free-breathing, non-ECG, simultaneous myocardial T1 , T2 , T2 *, and fat-fraction mapping with motion-resolved cardiovascular MR multitasking.

To develop a free-breathing, non-electrocardiogram technique for simultaneous myocardial T1 , T2 , T2 *, and fat-fraction (FF) mapping in a single scan. The MR Multitasking framework is adapted to quantify T1 , T2 , T2 *, and FF simultaneously. A variable TR scheme is developed to preserve temporal resolution and imaging efficiency. The underlying high-dimensional image is modeled as a low-rank tensor, which allows accelerated acquisition and efficient reconstruction. The accuracy and/or repeatability of the technique were evaluated on static and motion phantoms, 12 healthy volunteers, and 3 patients by comparing to the reference techniques. In static and motion phantoms, T1 /T2 /T2 */FF measurements showed substantial consistency (R > 0.98) and excellent agreement (intraclass correlation coefficient > 0.93) with reference measurements. In human subjects, the proposed technique yielded repeatable T1 , T2 , T2 *, and FF measurements that agreed with those from references. The proposed free-breathing, non-electrocardiogram, motion-resolved Multitasking technique allows simultaneous quantification of myocardial T1 , T2 , T2 *, and FF in a single 2.5-min scan.

Stein's method, heat kernel, and linear functions on the orthogonal groups

Combining Stein's method with heat kernel techniques, we study the function Tr(AO), where A is a fixed n×n matrix over R such that Tr(AAt)=n, and O is from the Haar measure of the orthogonal group O(n,R). It is shown that the total variation distance of the random variable Tr(AO) to a standard normal random variable is bounded by 22n−1, slightly improving the constant in a bound of Meckes, which was obtained by completely different methods.

Fast T1 measurement of cortical bone using 3D UTE actual flip angle imaging and single-TR acquisition (3D UTE-AFI-STR).

To describe a new method for accurate T1 measurement of cortical bone that fits the data sets of both 3D UTE actual flip angle imaging (UTE-AFI) and UTE with a single TR (UTE-STR) simultaneously (UTE-AFI-STR). To make both the constant values and longitudinal mapping functions in the signal equations for UTE-AFI and UTE-STR identical, the same RF pulses and flip angles were used. Therefore, there were three unknowns in the three equations. This was sufficient to fit the data. Numerical simulation as well as ex vivo and in vivo cortical bone studies were performed to validate the T1 measurement accuracy with the UTE-AFI-STR method. The original UTE-AFI variable TR (VTR) (ie, combined UTE-AFI and UTE with VTR) and simultaneous fitting (sf) of UTE-AFI and UTE-VTR (sf-UTE-AFI-VTR) methods were performed for comparison. The numerical simulation study showed that the UTE-AFI-STR method provided accurate value of T1 when the SNR of the UTE-STR image was higher than 40. The ex vivo study showed that the UTE-AFI-STR method measured the T1 of cortical bone accurately, with difference ratios ranging from -5.0% to 0.4%. The in vivo study showed a mean T1 of 246 ms with the UTE-AFI-STR method, and mean difference ratios of 2.4% and 5.0%, respectively, compared with the other two methods. The 3D UTE-AFI-STR method provides accurate mapping of the T1 of cortical bone with improved time efficiency compared with the UTE-AFI-VTR/sf-UTE-AFI-VTR methods.

Penerapan Risk Management Operational dan Pengaruhnya terhadap Mutu Pelayanan Di PT.UOB Property Jakarta

Implementation of operational risk management on the object property is very important in order to improve the quality of service so that the tenants more comfortable so that they continue to rent the premises. There are four divisions that are in direct contact with the occupants of the building that affect the quality of service that is division Tenant Relations, Engineering, Housekeeping and Security, therefore researchers interested in conducting research with the aim of knowing the operational risks of the building on the division Tenant Relations, Engineering, housekeeping and security and want to know the relationship of the four divisions with the quality of service. This research was conducted in PT.UOB PROPERTY with UOB Plaza building in Jakarta with population of 35 tenants and taken sample 25 respondents by using direct study in field and literature study, while to know the relationship of the four divisions with Spss 24 by using sample random sampling technique with 25 respondents. From the analysis results, there are operational risks with risk classification and low, medium and high impact in the TR (x1), Engineering (x2), Housekeeping (x3) and Security (x4) divisions.The results of the data using Spss 24 generated regression model Y = 0.353x1 + 0.585x2 + 0.567x3 - 0.040x4 - 3.621 and based on F test results that variable div.TR, Eng, HK, and div. Security variables simultaneously affect the variable the quality of the service, or by looking at the computation of F arithmetic with F table, from table F obtained data F table of 2.759, while F arithmetic of 43,070 thus F table (2.759) &lt;F count (43.070) or F count (43.070)&gt; F table (2.759) so that it can be concluded independent variable (X) div TR, Engineering, Housekeeping and Security simultaneously together affect the quality of service (Y), while based on test results t only engineering division (x2) , while for division Tenant relation, Housekeeping and security have no relation with service of quality.

To measure T1 of short T2 species using an inversion recovery prepared three-dimensional ultrashort echo time (3D IR-UTE) method: A phantom study

PurposeTo demonstrate the feasibility of a new method for measuring T1 of short T2 species based on an adiabatic inversion recovery-prepared three-dimensional ultrashort echo time Cones (3D IR-UTE-Cones) sequence. MethodsT1 values for short T2 species were quantified using 3D IR-UTE-Cones data acquired with different repetition times (TRs) and inversion times (TIs). An inversion efficiency factor Q was introduced into the fitting model to accurately calculate T1 values for short T2 species. Experiments were performed on twelve MnCl2 aqueous solution phantoms with a wide range of T1 values and T2* values on a 3 T clinical MR system to verify the efficacy of the proposed method. For comparison, a variable flip angle UTE (VFA-UTE) sequence, a variable TR UTE (VTR-UTE) sequence, and a conventional 2D IR fast spin echo (IR-FSE) sequence were also used to quantify T1 values of those phantoms. T1 values were compared between all performed sequences. ResultsThe proposed 3D IR-UTE-Cones method provided higher contrast images of short T2 phantoms and measured much shorter T1 values than the VFA-UTE, VTR-UTE and 2D IR-FSE methods. T1 values as short as 2.95 ms could be measured by the 3D IR-UTE-Cones sequence. The 3D IR-UTE-Cones methods with different TRs were applied to different ranges of T1 measurement, and the scan time was significantly decreased by using 5 TIs along the recovery curves to perform fitting with comparable accuracy. ConclusionThe 3D IR-UTE-Cones sequence could accurately measure short T1 values while providing high contrast images of short T2 species.

Reduced respiratory motion artefact in constant TR multi-slice MRI of the mouse

PurposeMulti-slice scanning in the abdomen and thorax of small animals is compromised by the effects of respiration unless imaging and respiration are synchronised. To avoid the signal modulations that result from respiration motion and a variable TR, blocks of fully relaxed slices are typically acquired during inter-breath periods, at the cost of scan efficiency. This paper reports a conceptually simple yet effective prospective gating acquisition mode for multi-slice scanning in free breathing small animals at any fixed TR of choice with reduced sensitivity to respiratory motion. MethodsMulti-slice scan modes have been implemented in which each slice has its own specific projection or phase encode loop index counter. When a breath is registered RF pulses continue to be applied but data are not acquired, and the corresponding counters remain fixed so that the data are acquired one TR later, providing it coincides with an inter-breath period. The approach is refined to reacquire the slice data that are acquired immediately before each breath is detected. Only the data with reduced motion artefact are used in image reconstruction. The efficacy of the method is demonstrated in the RARE scan mode which is well known to be particularly useful for tumour visualization. ResultsValidation in mice with RARE demonstrates improved stability with respect to ungated scanning where signal averaging is often used to reduce artefacts. SNR enhancement maps demonstrate the improved efficiency of the proposed method that is equivalent to at least a 2.5 fold reduction in scan time with respect to ungated signal averaging. A steady-state magnetisation transfer contrast prepared gradient echo implementation is observed to highlight tumour structure. Supplementary simulations demonstrate that only small variations in respiration rate are required to enable efficient sampling with the proposed method. ConclusionsThe proposed prospective gating acquisition scheme enables efficient multi-slice scanning in small animals at the optimum TR with reduced sensitivity to respiratory motion. The method is compatible with a wide range of complementary methods including non-Cartesian scan modes, partially parallel imaging, and compressed sensing. In particular, the proposed scheme reduces the need for continual close monitoring to effect operator intervention in response to respiratory rate changes, which is both difficult to maintain and precludes high throughput.

Multiparametric characterization of response to anti-angiogenic therapy using USPIO contrast-enhanced MRI in combination with dynamic contrast-enhanced MRI.

Steady state susceptibility contrast (SSC)-MRI provides information on vascular morphology but is a rarely used method. To investigate the utility of the ultrasmall superparamagnetic iron oxide particles (USPIOs) GEH121333 for measuring tumor response to bevacizumab and compare this with gadolinium-based DCE-MRI. Prospective preclinical animal model study. Mice bearing subcutaneous TOV-21G human ovarian cancer xenografts treated with bevacizumab (n = 9) or saline (n = 9). Imaging was performed on a 7T Bruker Biospec. For SSC-MRI with GEH121333 we acquired R1 -maps (RARE-sequence with variable TR), R2 -maps (multi-spin echo), and R2*-maps (multi-gradient echo). Additionally, R1 and R2 maps were measured on the days after USPIO injection. For DCE-MRI with gadodiamide we acquired 200 T1 -weighted images (RARE-sequence). ΔR1 , ΔR2 , and ΔR2* maps were computed from SSC-MRI. DCE-MRI was analysed using the extended Tofts model. Results from pre- and 3 days posttreatment SSC-MRI were compared using paired-sample t-tests. Treatment and control groups were compared using independent sample t-tests. Performance of SSC- and DCE-MRI was compared using multivariate partial least squares discriminant analysis. Already one day after treatment and USPIO injection, R1 and R2 values were lower in treated (R1 = 0.49 ± 0.03s-1 , R2 = 23.07 ± 1.49s-1 ) compared with control tumors (R1 = 0.52 ± 0.02s-1 , R2 = 24.98 ± 1.01s-1 ), indicating lower USPIO accumulation. Posttreatment SSC-MRI displayed significantly decreased tumor blood volume (change in ΔR2 = -0.43 ± 0.26s-1 , P = 0.001) and vessel density (change in Q = -0.032 ± 0.020s-1/3 , P = 0.002). DCE-MRI showed among others lower Ktrans in treated tumors (control = 0.064 ± 0.011min-1 , tx = 0.046 ± 0.008min-1 , P = 0.002). Multivariate analysis suggests that SSC-MRI was slightly inferior to DCE-MRI in distinguishing treated from control tumors (accuracy = 75%, P = 0.058 versus 80%, P = 0.028), but a combination of both was best (accuracy = 85%; P = 0.003). SSC-MRI with GEH121333 is sensitive to early (<24 h) and late changes in tumor vasculature. SSC-MRI and DCE-MRI provide complementary information and can be used to assess different aspects of vascular responses to anti-angiogenic therapies. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1589-1600.

PNFLBA-14 EARLY IN VIVO DETECTION OF METASTATIC BLADDER CANCER IN MICE USING MOLECULAR MRI

You have accessJournal of UrologyPlenary: Next Frontier (PNFLBA)1 Apr 2017PNFLBA-14 EARLY IN VIVO DETECTION OF METASTATIC BLADDER CANCER IN MICE USING MOLECULAR MRI Joel Slaton, Nataliya Smith, Debra Saunders, Robert Hurst, and Rheal Towner Joel SlatonJoel Slaton More articles by this author , Nataliya SmithNataliya Smith More articles by this author , Debra SaundersDebra Saunders More articles by this author , Robert HurstRobert Hurst More articles by this author , and Rheal TownerRheal Towner More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.03.040AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Early detection of bladder cancer metastases might provide the potential for early treatment of metastatic disease. We previously reported on the use of a bladder tumor-binding peptide (BTBP)2 coupled to a Gd-DOTA MRI contrast agent (BTBP-probe)3 delivered intravesically to visualize bladder cancer growing on the bladder surface of an orthotopic mouse model, In this new report we demonstrated the use of this probe delivered intravenously to detect micrometastic spread of cancer to distant organs. METHODS MRI Studies: MRI experiments were done on a Bruker Biospec 7.0 Tesla/30 cm horizontal-bore imaging system. Multiple abdominal region 1H-MR image slices were taken using a RARE multislice (repetition time (TR) 1.3 s, echo time (TE) 9 ms, 256x256 matrix, 4 steps per acquisition, 3x3 cm2 field of view, 0.75 mm slice thickness). Mouse abdominal organs were imaged at 0 (pre-contrast) and at 3-4 hours post-contrast agent injection. Mice were injected intravenously with the BTBP-Gd-DOTA contrast agent (100μl/mouse; 50μmol/L). T1-weighted images were obtained using a variable TR (repetition time) spin-echo sequence (TR, 200-1600 ms; TE, 15 ms; NA, 2). Pixel-by-pixel relaxation maps were reconstructed from a series of T1-weighted images using a nonlinear two-parameter fitting procedure. The T1 value of a specified region-of-interest (ROI) was computed from all the pixels in the identified ROIs. MRI scans were obtained 6-7 weeks post-implantation of bladder tumors to identiy metastatic lesions. RESULTS Molecular MRI (mMRI) was used to detect the presence of the BTBP-probe via a substantial decrease in T1 relaxation, measured as T1 relaxation difference, within tumor regions of mice administered the BTBP-probe (p<0.05) compared to the controls. Both primary and metastatic tumors were detected. CONCLUSIONS We used mMRI to show for the first time non-invasive in vivo early detection of bladder tumor metastases in a mouse model for bladder carcinoma. Using mMRI with a bladder tumor-binding peptide targeted probe provides the advantage of in vivo image resolution and spatial differentiation of regional events in early detection of bladder cancer metastases. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e916 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Joel Slaton More articles by this author Nataliya Smith More articles by this author Debra Saunders More articles by this author Robert Hurst More articles by this author Rheal Towner More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

The correction of time and temperature effects in MR-based 3D Fricke xylenol orange dosimetry

Previously developed MR-based three-dimensional (3D) Fricke-xylenol orange (FXG) dosimeters can provide end-to-end quality assurance and validation protocols for pre-clinical radiation platforms. FXG dosimeters quantify ionizing irradiation induced oxidation of Fe2+ ions using pre- and post-irradiation MR imaging methods that detect changes in spin-lattice relaxation rates (R1 = ) caused by irradiation induced oxidation of Fe2+. Chemical changes in MR-based FXG dosimeters that occur over time and with changes in temperature can decrease dosimetric accuracy if they are not properly characterized and corrected. This paper describes the characterization, development and utilization of an empirical model-based correction algorithm for time and temperature effects in the context of a pre-clinical irradiator and a 7 T pre-clinical MR imaging system.Time and temperature dependent changes of R1 values were characterized using variable TR spin-echo imaging. R1-time and R1-temperature dependencies were fit using non-linear least squares fitting methods. Models were validated using leave-one-out cross-validation and resampling. Subsequently, a correction algorithm was developed that employed the previously fit empirical models to predict and reduce baseline R1 shifts that occurred in the presence of time and temperature changes. The correction algorithm was tested on R1-dose response curves and 3D dose distributions delivered using a small animal irradiator at 225 kVp.The correction algorithm reduced baseline R1 shifts from −2.8 × 10−2 s−1 to 1.5 × 10−3 s−1. In terms of absolute dosimetric performance as assessed with traceable standards, the correction algorithm reduced dose discrepancies from approximately 3% to approximately 0.5% (2.90 ± 2.08% to 0.20 ± 0.07%, and 2.68 ± 1.84% to 0.46 ± 0.37% for the 10 × 10 and 8 × 12 mm2 fields, respectively).Chemical changes in MR-based FXG dosimeters produce time and temperature dependent R1 values for the time intervals and temperature changes found in a typical small animal imaging and irradiation laboratory setting. These changes cause baseline R1 shifts that negatively affect dosimeter accuracy. Characterization, modeling and correction of these effects improved in-field reported dose accuracy to less than 1% when compared to standardized ion chamber measurements.

Optimization of sparse phase encodings for variable repetition-delay turbo-spin echo (TSE) T1 measurements for preclinical applications

A variable repetition-delay (TR) spin echo sequence with repeated refocusing pulses, i.e., a variable TR turbo-spin echo (TSE), provides an attractive means of acquiring an accurate T1 map information that is free from gradient echo based artifacts such as magnetic field inhomogeneities particularly for ultra-high field (at 7T and above) preclinical applications. However, the applicability of multi-slice TSE sequences is often limited by signal distortion from T2 relaxation due to echo-train acquisitions for short T2 tissues, inter-slice cross talks and magnetization transfer (MT) from repetitive slice-selective 180° pulse, and extended scan times with multiple TR excitations. These TSE shortcomings are difficult to remedy for preclinical applications, where small sizes of target organs usually limit the slice-gap control with restricted parallel imaging capabilities. In this study, compressed-sensing-assisted turbo-spin echo (CS-TSE) acquisitions for variable TR T1 measurements at 7T preclinical scanner were implemented to reduce the echo-trains by sparse phase encodings. Following the sparse signal simulation and sampling scheme optimization, the measured T1 values from CS-TSE and TSE were compared for phantoms, ex vivo, and in vivo subjects. The phantom T1 values from CS-TSE and TSE were identical to those from the inversion recovery spin echo. For both ex vivo and in vivo multi-slice T1 mapping, the shortened echo-trains of CS-TSE relieved the T2 relaxation, reduced the inter-slice interferences of multi-slice acquisition, and made room for additional slice encodings while maintaining a shorter scan time than the conventional TSE at the expense of local image smoothness from CS regularizations.

Simultaneous multislice magnetic resonance fingerprinting (SMS-MRF) with direct-spiral slice-GRAPPA (ds-SG) reconstruction.

To develop a reconstruction method to improve SMS-MRF, in which slice acceleration is used in conjunction with highly undersampled in-plane acceleration to speed up MRF acquisition. In this work two methods are employed to efficiently perform the simultaneous multislice magnetic resonance fingerprinting (SMS-MRF) data acquisition and the direct-spiral slice-GRAPPA (ds-SG) reconstruction. First, the lengthy training data acquisition is shortened by employing the through-time/through-k-space approach, in which similar k-space locations within and across spiral interleaves are grouped and are associated with a single set of kernel. Second, inversion recovery preparation (IR prepped), variable flip angle (FA), and repetition time (TR) are used for the acquisition of the training data, to increase signal variation and to improve the conditioning of the kernel fitting. The grouping of k-space locations enables a large reduction in the number of kernels required, and the IR-prepped training data with variable FA and TR provide improved ds-SG kernels and reconstruction performance. With direct-spiral slice-GRAPPA, tissue parameter maps comparable to that of conventional MRF were obtained at multiband (MB) = 3 acceleration using t-blipped SMS-MRF acquisition with 32-channel head coil at 3 Tesla (T). The proposed reconstruction scheme allows MB = 3 accelerated SMS-MRF imaging with high-quality T1 , T2 , and off-resonance maps, and can be used to significantly shorten MRF acquisition and aid in its adoption in neuro-scientific and clinical settings. Magn Reson Med 77:1966-1974, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Some new results on the eigenvalues of complex non-central Wishart matrices with a rank-1 mean

Let W be an n × n complex non-central Wishart matrix with m ( ≥ n ) degrees of freedom and a rank-1 mean. In this paper, we consider three problems related to the eigenvalues of W . To be specific, we derive a new expression for the cumulative distribution function (c.d.f.) of the minimum eigenvalue ( λ min ) of W . The c.d.f. is expressed as the determinant of a square matrix, the size of which depends only on the difference m − n . This further facilitates the analysis of the microscopic limit of the minimum eigenvalue. The microscopic limit takes the form of the determinant of a square matrix with its entries expressed in terms of the modified Bessel functions of the first kind. We also develop a moment generating function based approach to derive the probability density function of the random variable tr ( W ) / λ min , where tr ( ⋅ ) denotes the trace of a square matrix. Moreover, we establish that, as m , n → ∞ with m − n fixed, tr ( W ) / λ min scales like n 3 . Finally, we find the average of the reciprocal of the characteristic polynomial det [ z I n + W ] , | arg z | < π , where I n and det [ ⋅ ] denote the identity matrix of size n and the determinant, respectively.

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

SU‐E‐T‐606: Performance of MR‐Based 3D FXG Dosimetry for Preclinical Irradiation

Purpose:Technological advances have revolutionized preclinical radiation research to enable precise radiation delivery in preclinical models. Kilovoltage x‐rays and complex geometries in preclinical radiation studies challenge conventional dosimetry methods. Previously developed gel‐based dosimetry provides a viable means of accommodating complex geometries and accurately reporting dose at kV energies. This paper will describe the development and evaluation of gel‐based ferrous xylenol‐orange (FXG) dosimetry using a 7T preclinical imaging system.Methods:To confirm water equivalence, Zeff values were calculated for the FXG material, water and ICRU defined soft tissue. Proton T1 relaxivity response in FXG was measured using a preclinical 7T MR and a small animal irradiator for a dose range of 1–22 Gy. FXG was contained in 50 ml centrifuge tubes and irradiated with a 225 kVp x‐ray beam at a nominal dose rate of 2.3 Gy/min. Pre and post irradiation maps of the T1 relaxivity were collected using variable TR spin‐echo imaging (TE 6.65 ms; TR 500, 750, 1000, 1500, 2000, 3000 and 5000 ms) with 2 mm thick slices, 0.325 mm/pixel, 3 averages and an acquisition time of 26 minutes. A linear fit to the change in relaxation rate (1/T1) for the delivered doses reported the gel sensitivity in units of ms‐1Gy‐1. Irradiation and imaging studies were repeated using three batches of gel over 72 hrs.Results:FXG has a Zeff of 3.8 for the 225 kVp spectrum used; differing from water and ICRU defined soft tissue by 0.5% and 2.5%, respectively. The average sensitivity for the FXG dosimeter was 31.5 ± 0.7 ms‐1Gy‐1 (R2 = 0.9957) with a y‐intercept of −29.4 ± 9.0 ms‐1.Conclusion:Preliminary results for the FXG dosimeter properties, sensitivity, and dose linearity at preclinical energies is promising. Future work will explore anatomically relevant tissue inclusions to test MR performance.Student funding provided by The Terry Fox Foundation Strategic Initiative for Excellence in Radiation Research for the 21st Century at CIHR and the Gifford Ontario Student Opportunity Trust Fund.

ECG gated 3D single shot FSE with variable TR for non-contrast peripheral MRA at 3T

ECG gated 3D single shot FSE with variable TR for non-contrast peripheral MRA at 3T

Multi-TI Arterial Spin Labeling MRI with Variable TR and Bolus Duration for Cerebral Blood Flow and Arterial Transit Time Mapping.

Arterial spin labeling (ASL) is an MRI perfusion imaging method from which quantitative cerebral blood flow (CBF) can be calculated. We present a multi-TI ASL method (multi-TI integrated ASL) in which variable post-labeling delays and variable TRs are used to improve the estimation of arterial transit time (ATT) and CBF while shortening the scan time by 41% compared to the conventional methods. Variable bolus widths allow for T1 and M0 estimation from raw ASL data. Multi-TI integrated pseudo-continuous ASL images were collected at 7 TI times ranging 100-4300 ms. Voxel-wise T1 and M0 maps were estimated, then CBF and ATT maps were created using the estimated T1 tissue map. All maps were consistent with physiological values reported in the literature. Based on simulations and in vivo comparisons, this method demonstrates higher CBF and ATT estimation efficiency than other ATT acquisition methods and better fit to the perfusion model. It produces CBF maps with reduced sensitivity to errors from ATT and tissue T1 variations. The estimated M0, T1, and ATT maps also have potential clinical utility. The method requires a single scan acquired within a clinically acceptable scan time (under 6 minutes) and with low sensitivity to motion.

O-014 Modelling Unstable Brain Aneurysms: MR Molecular Imaging of Myeloperoxidase in the Aneurysm Wall and Correlation with Human Pathology

IntroductionAn imaging approach identifying patients who benefit from treatment of unruptured intracranial aneurysms (UIA) is desired. We investigate a potential biomarker of UIA instability, myeloperoxidase (MPO), in human aneurysm tissue...

Contrast-enhanced intracranial magnetic resonance angiography with a spherical shells trajectory and online gridding reconstruction

To evaluate the feasibility of applying the shells trajectory to single-phase contrast-enhanced magnetic resonance angiography. Several methods were developed to overcome the challenges of the clinical implementation of shells including off-resonance blurring (eg, from lipid signal), aliasing artifacts, and long reconstruction times. These methods included: 1) variable TR with variable readout length to reduce fat signal and off-resonance blurring; 2) variable sampling density to suppress aliasing artifacts while minimizing acquisition time penalty; and 3) an online 3D gridding algorithm that reconstructed an 8-channel, 240(3) image volume set. Both phantom and human studies were performed to establish the initial feasibility of the methods. Phantom and human study results demonstrated the effectiveness of the proposed methods. Shells with variable TR and readout length further suppressed the fat signal compared to the fixed-TR shells acquisition. Reduced image aliasing was achieved with minimal scan time penalty when a variable sampling density technique was used. The fast online reconstruction algorithm completed in 2 minutes at the scanner console, providing a timely image display in a clinical setting. It was demonstrated that the use of the shells trajectory is feasible in a clinical setting to acquire intracranial angiograms with high spatial resolution. Preliminary results demonstrate effective venous suppression in the cavernous sinuses and jugular vein region.

Signal fluctuations induced by non‐T1‐related confounds in variable TR fMRI experiments

To assess and model signal fluctuations induced by non-T(1)-related confounds in variable repetition time (TR) functional magnetic resonance imaging (fMRI) and to develop a compensation procedure to correct for the non-T(1)-related artifacts. Radiofrequency disabled volume gradient sequences were effected at variable offsets between actual image acquisitions, enabling perturbation of the measurement system without perturbing longitudinal magnetization, allowing the study of non-T(1)-related confounds that may arise in variable TR experiments. Three imaging sessions utilizing a daily quality assurance (DQA) phantom were conducted to assess the signal fluctuations, which were then modeled as a second-order system. A modified projection procedure was implemented to correct for signal fluctuations arising from non-T(1)-related confounds, and statistical analysis was performed to assess the significance of the artifacts with and without compensation. Assessment using phantom data reveals that the signal fluctuations induced by non-T(1)-related confounds was consistent in shape across the phantom and well-modeled by a second-order system. The phantom exhibited significant spurious detections (at P < 0.01) almost uniformly across the central slices of the phantom. Second-order system modeling and compensation of non-T(1)-related confounds achieves significant reduction of spurious detection of fMRI activity in a phantom.