Toward an Intravoxel Incoherent Motion 2-in-1 Magnetic Resonance Imaging Sequence for Ischemic Stroke Diagnosis? An Initial Clinical Experience With 1.5T Magnetic Resonance.

OBJECTIVE: This initial study aimed to investigate the feasibility of simultaneously measuring perfusion and diffusion including kurtosis features in acute ischemic stroke with the combined intravoxel incoherent motion and non-Gaussian diffusional kurtosis imaging (DKI-IVIM). MATERIAL AND METHODS: Five ischemic stroke patients underwent a 4-minute diffusion weighted imaging (DWI) protocol, using 8 b values chosen with the Cramer-Rao-Lower-Bound optimization approach, in addition to conventional DWI and arterial spin labeling sequences. Regions of interest in pathological and control regions were analyzed with DKI-IVIM, and parametric maps were reconstructed. RESULTS: The IVIM diffusion coefficient (D) decreased (P < 0.0001) in the infarcted areas, whereas higher kurtosis coefficient values were found (P = 0.0002). Regarding the perfusion, the individual IVIM perfusion fraction f decreased in 3 matching cases with the cerebral blood flow estimated through arterial spin labeling and the fD* decreased only in 2 patients of those. CONCLUSIONS: When compared with conventional stroke imaging protocol, DKI-IVIM 4-minute 2-in-1 acquisition can provide diffusion results comparable with conventional DWI with complementary kurtosis estimations but a limited robustness regarding perfusion estimations for clinical purpose.

High-resolution multi-T1 -weighted contrast and T1 mapping with low B1>+ sensitivity using the fluid and white matter suppression (FLAWS) sequence at 7T.

PURPOSE: To demonstrate that fluid and white matter suppression (FLAWS) imaging can be used for high-resolution T1 mapping with low transmitted bias field ( B1+ ) sensitivity at 7T. METHODS: The FLAWS sequence was optimized for 0.8-mm isotropic resolution imaging. The theoretical accuracy and precision of the FLAWS T1 mapping was compared with the one of the magnetization-prepared two rapid gradient echoes (MP2RAGE) sequence optimized for low B1+ sensitivity. FLAWS images were acquired at 7T on six healthy volunteers (21 to 48 years old; two women). MP2RAGE and saturation-prepared with two rapid gradient echoes (SA2RAGE) datasets were also acquired to obtain T1 mapping references and B1+ maps. The contrast-to-noise ratio (CNR) between brain tissues was measured in the FLAWS-hco and MP2RAGE-uni images. The Pearson correlation was measured between the MP2RAGE and FLAWS T1 maps. The effect of B1+ on FLAWS T1 mapping was assessed using the Pearson correlation. RESULTS: The FLAWS-hco images were characterized by a higher brain tissue CNR ( CNRWM/GM=5.5 , CNRWM/CSF=14.7 , CNRGM/CSF=10.3 ) than the MP2RAGE-uni images ( CNRWM/GM=4.9 , CNRWM/CSF=6.6 , CNRGM/CSF=3.7 ). The theoretical accuracy and precision of the FLAWS T1 mapping ( acc=91.9%;prec=90.2% ) were in agreement with those provided by the MP2RAGE T1 mapping ( acc=90.0%;prec=86.8% ). A good agreement was found between in vivo T1 values measured with the MP2RAGE and FLAWS sequences (r = 0.91). A weak correlation was found between the FLAWS T1 map and the B1+ map within cortical gray matter and white matter segmentations ( rWM=-0.026 ; rGM=0.081 ). CONCLUSION: The results from this study suggest that FLAWS is a good candidate for high-resolution T1 -weighted imaging and T1 mapping at the field strength of 7T.

Voxel-based mapping of five MR biomarkers in the wrist bone marrow.

OBJECTIVE: MRI is a reliable and accurate technique to characterize rheumatoid arthritis. The aim of this study was to provide voxel-by-voxel 3D maps of the proton density fat fraction (PDFF), the T1 of water (T1W), the T1 of fat (T1F), the T2* of water (T2*W), the T2* of fat (T2*F) in the wrist bone marrow. MATERIALS AND METHODS: The experiments were conducted on 14 healthy volunteers (mean age: 24 ± 4). The data were acquired at 1.5 T using two optimized four-echo 3D 1.2 × 1.2 × 1.2 mm3-isotropic spoiled gradient sequences. A repeatability study was carried out. The measurements were done using a homemade parametric viewer software. RESULTS: The inter-volunteer results were, on average: PDFF = 86 ± 3%, T1W = 441 ± 113 ms, T1F = 245 ± 19 ms, T2*W = 6 ± 1 ms and T2*F = 16 ± 3 ms. The coefficients of variation were for fat based biomarkers CVPDFF < 5%, CVT1F < 15% and CVT2*F < 10% in the repeatability study. DISCUSSION: The protocol and quantification tool proposed in this study provide high-resolution voxel-by-voxel 3D maps of five biomarkers in the wrist in less than 4 min of acquisition.

Measurements of Diffusion and Perfusion in Vertebral Bone Marrow Using Intravoxel Incoherent Motion (IVIM) With Multishot, Readout-Segmented (RESOLVE) Echo-Planar Imaging.

BACKGROUND: A limited number of studies have used the intravoxel incoherent motion (IVIM) approach on bone marrow. In none of the previous studies were the effects of fat suppression on the IVIM parameters investigated. PURPOSE: To measure the water diffusion coefficient and the perfusion fraction in vertebral bone marrow using IVIM with multishot, readout-segmented (RESOLVE) echo-planar imaging and to assess the effects of different fat suppression techniques on the measurement of the IVIM parameters. STUDY TYPE: Prospective. POPULATION/SUBJECTS: Six healthy volunteers (24.2 ± 4.3 years). FIELD STRENGTH/SEQUENCE: 1.5T, RESOLVE. ASSESSMENT: Four experiments were performed: 1) RESOLVE imaging without fat suppression, 2) with fat saturation (FS), 3) with spectral attenuated inversion recovery (SPAIR), and 4) with short-tau inversion recovery (STIR). The water diffusion coefficient D, pseudo-diffusion coefficient D*, and the perfusion fraction f were assessed in the vertebral bodies of the lumbar vertebrae. STATISTICAL TESTS: One-way repeated-measures analysis of variance (ANOVA) followed by Bonferroni's multiple comparison test. RESULTS: The RESOLVE IVIM protocol allowed for measurement of D, D*, and f in all volunteers. The signal of lipid protons affected the quantification of the IVIM diffusion coefficient: D = 0.24 ± 0.10 (×10-3 mm2 /s), no FS; D = 0.43 ± 0.07 (×10-3 mm2 /s), FS; D = 0.42 ± 0.07 (×10-3 mm2 /s), SPAIR; D = 0.35 ± 0.10 (×10-3 mm2 /s), STIR; and IVIM perfusion fraction f = 7.5 ± 1.9% no FS, f = 14.5 ± 5.4%, FS; f = 12.5 ± 2.6%, SPAIR; f = 18.1 ± 6.1%, STIR. No significant effect (P = 0.36) was found on the quantification of D*. DATA CONCLUSION: An IVIM-MRI protocol using the RESOLVE sequence was implemented for measurements of vertebral bone marrow diffusion and the perfusion. The comparison between the protocols with and without fat suppression indicates that the lipid signal results in an underestimation of both D and f. LEVEL OF EVIDENCE: Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;49:768-776.

Tissue oxygenation mapping by combined chemical shift and T1 magnetic resonance imaging.

PURPOSE: To propose a method for determining tissue oxygenation via the measurement of fat T1 . The method is based on a 2D fat/water chemical shift-encoded and T1 -weighted acquisition. THEORY AND METHODS: A 2D data set was acquired with a fast spin echo sequence with several echo asymmetries and repetition times, wherein one dimension is related to the fat/water phase modulation and the other to the T1 saturation recovery. A joint magnitude-based process of phase modulation and T1 evolution allowed for the collection of the fat fraction and T1 maps with resolved fat or water dominance ambiguity while avoiding the phased error problem. RESULTS: In vitro imaging allowed for the attribution of fat content for different water/oil emulsions that demonstrated longitudinal relaxation rate (R1 ) sensitivity to the oxygenated emulsion environment. The fat R1 values were subsequently compared to reference values, which were measured using low receiver bandwidth acquisition to enhance water and fat signal separations. In vivo feasibility of tissue oxygenation assessment was demonstrated by investigating interscapular brown adipose tissue modifications during an air/carbogen challenge in rats. CONCLUSION: The proposed method offers a precise and robust estimate of tissue oxygenation illustrated by the method's ability to detect-brown adipose tissue oxygenation modifications. Magn Reson Med 79:1981-1991, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Non-invasive measurement of liver iron concentration using 3-Tesla magnetic resonance imaging: validation against biopsy.

OBJECTIVES: To evaluate the performance and limitations of the R2* and signal intensity ratio (SIR) methods for quantifying liver iron concentration (LIC) at 3 T. METHODS: A total of 105 patients who underwent a liver biopsy with biochemical LIC (LICb) were included prospectively. All patients underwent a 3-T MRI scan with a breath-hold multiple-echo gradient-echo sequence (mGRE). LIC calculated by 3-T SIR algorithm (LICSIR) and by R2* (LICR2*) were correlated with LICb. Sensitivity and specificity were calculated. The comparison of methods was analysed for successive classes. RESULTS: LICb was strongly correlated with R2* (r = 0.95, p < 0.001) and LICSIR (r = 0.92, p < 0.001). In comparison to LICb, LICR2* and LICSIR detect liver iron overload with a sensitivity/specificity of 0.96/0.93 and 0.92/0.95, respectively, and a bias ± SD of 7.6 ± 73.4 and 14.8 ± 37.6 µmol/g, respectively. LICR2* presented the lowest differences for patients with LICb values under 130 µmol/g. Above this value, LICSIR has the lowest differences. CONCLUSIONS: At 3 T, R2* provides precise LIC quantification for lower overload but the SIR method is recommended to overcome R2* limitations in higher overload. Our software, available at www.mrquantif.org , uses both methods jointly and selects the best one. KEY POINTS: • Liver iron can be accurately quantified by MRI at 3 T • At 3 T, R2* provides precise quantification of slight liver iron overload • At 3 T, SIR method is recommended in case of high iron overload • Slight liver iron overload present in metabolic syndrome can be depicted • Treatment can be monitored with great confidence.

Measuring Cerebral Hypoperfusion Induced by Hyperventilation Challenge With Intravoxel Incoherent Motion Magnetic Resonance Imaging in Healthy Volunteers.

OBJECTIVES: The aim of this study was to demonstrate the feasibility to assess cerebral hypoperfusion with a hyperventilation (HV) challenge protocol using intravoxel incoherent motion (IVIM) magnetic resonance imaging. MATERIALS AND METHODS: Magnetic resonance imaging experiments were performed on 10 healthy volunteers at 1.5 T, with a diffusion IVIM magnetic resonance imaging protocol using a set of b-values optimized by Cramer-Rao Lower Bound analysis. Hypoperfusion was induced by an HV maneuver. Measurements were performed in normoventilation and HV conditions. Biexponential curve fitting was used to obtain the perfusion fraction (f), pseudodiffusion coefficient (D*), and the product fD* in gray matter (GM) regions of interest (ROIs). Regional cerebral blood flow in the same ROIs was also assessed with arterial spin labeling. RESULTS: The HV challenge led to a diminution of IVIM perfusion-related parameters, with a decrease of f and fD* in the cerebellum (P = 0.03 for f; P = 0.01 for fD*), thalamus GM (P = 0.09 for f; P = 0.01 for fD*), and lenticular nuclei (P = 0.03 for f; P = 0.02 for fD*). Mean GM cerebral blood flow (in mL/100 g tissue/min) measured with arterial spin labeling averaged over all ROIs also decreased (normoventilation: 42.7 ± 4.1 vs HV: 33.2 ± 2.2, P = 0.004) during the HV challenge. CONCLUSIONS: The optimized IVIM protocol proposed in the current study allows for measurements of cerebral hypoperfusion that might be of great interest for pathologies diagnosis such as ischemic stroke.

Partial volume model for brain MRI scan using MP2RAGE.

MP2RAGE is a T1 weighted MRI sequence that estimates a composite image providing much reduction of the receiver bias, has a high intensity dynamic range, and provides an estimate of T1 mapping. It is, therefore, an appealing option for brain morphometry studies. However, previous studies have reported a difference in cortical thickness computed from MP2RAGE compared with widely used Multi-Echo MPRAGE. In this article, we demonstrated that using standard segmentation and partial volume estimation techniques on MP2RAGE introduces systematic errors, and we proposed a new model to estimate partial volume of the cortical gray matter. We also included in their model a local estimate of tissue intensity to take into account the natural variation of tissue intensity across the brain. A theoretical framework is provided and validated using synthetic and physical phantoms. A repeatability experiment comparing MPRAGE and MP2RAGE confirmed that MP2RAGE using our model could be considered for structural imaging in brain morphology study, with similar cortical thickness estimate than that computed with MPRAGE. Hum Brain Mapp 38:5115-5127, 2017. © 2017 Wiley Periodicals, Inc.

Eliminating the blood-flow confounding effect in intravoxel incoherent motion (IVIM) using the non-negative least square analysis in liver.

PURPOSE: Tissue perfusion measurements using intravoxel incoherent motion (IVIM) diffusion-MRI are of interest for investigations of liver pathologies. A confounding factor in the perfusion quantification is the partial volume between liver tissue and large blood vessels. The aim of this study was to assess and correct for this partial volume effect in the estimation of the perfusion fraction. METHODS: MRI experiments were performed at 3 Tesla with a diffusion-MRI sequence at 12 b-values. Diffusion signal decays in liver were analyzed using the non-negative least square (NNLS) method and the biexponential fitting approach. RESULTS: In some voxels, the NNLS analysis yielded a very fast-decaying component that was assigned to partial volume with the blood flowing in large vessels. Partial volume correction was performed by biexponential curve fitting, where the first data point (b = 0 s/mm2 ) was eliminated in voxels with a very fast-decaying component. Biexponential fitting with partial volume correction yielded parametric maps with perfusion fraction values smaller than biexponential fitting without partial volume correction. CONCLUSION: The results of the current study indicate that the NNLS analysis in combination with biexponential curve fitting allows to correct for partial volume effects originating from blood flow in IVIM perfusion fraction measurements. Magn Reson Med 77:310-317, 2017. © 2016 Wiley Periodicals, Inc.

In vivo MRS for the assessment of mouse colon using a dedicated endorectal coil: initial findings.

Inflammatory bowel disease is a common group of inflammation conditions that can affect the colon and the rectum. These pathologies require a careful follow-up of patients to prevent the development of colorectal cancer. Currently, conventional endoscopy is used to depict alterations of the intestinal walls, and biopsies are performed on suspicious lesions for further analysis (histology). MRS enables the in vivo analysis of biochemical content of tissues (i.e. without removing any samples). Combined with dedicated endorectal coils (ERCs), MRS provides new ways of characterizing alterations of tissues. An MRS in vivo protocol was specifically set up on healthy mice and on mice chemically treated to induce colitis. Acquisitions were performed on a 4.7 T system using a linear volume birdcage coil for the transmission of the B1 magnetic field, and a dedicated ERC was used for signal reception. Colon-wall complex, lumen and visceral fat were assessed on healthy and treated mice with voxel sizes ranging from 0.125 µL to 2 µL while keeping acquisition times below 3 min. The acquired spectra show various biochemical contents such as α- and ß-methylene but also glycerol backbone and diacyl. Choline was detected in tumoral regions. Visceral fat regions display a high lipid content with no water, whereas colon-wall complex exhibits both high lipid and high water contents. To the best of our knowledge, this is the first time that in vivo MRS using an ERC has been performed in the assessment of colon walls and surrounding structures. It provides keys for the in vivo characterization of small local suspicious lesions and offers complementary solutions to biopsies.

Diffusional kurtosis imaging (DKI) incorporation into an intravoxel incoherent motion (IVIM) MR model to measure cerebral hypoperfusion induced by hyperventilation challenge in healthy subjects.

OBJECTIVES: The objectives were to investigate the diffusional kurtosis imaging (DKI) incorporation into the intravoxel incoherent motion (IVIM) model for measurements of cerebral hypoperfusion in healthy subjects. MATERIALS AND METHODS: Eight healthy subjects underwent a hyperventilation challenge with a 4-min diffusion weighted imaging protocol, using 8 b values chosen with the Cramer-Rao Lower Bound optimization approach. Four regions of interest in gray matter (GM) were analyzed with the DKI-IVIM model and the bi-exponential IVIM model, for normoventilation and hyperventilation conditions. RESULTS: A significant reduction in the perfusion fraction (f) and in the product fD* of the perfusion fraction with the pseudodiffusion coefficient (D*) was found with the DKI-IVIM model, during the hyperventilation challenge. In the cerebellum GM, the percentage changes were f: -43.7 ± 40.1, p = 0.011 and fD*: -50.6 ± 32.1, p = 0.011; in thalamus GM, f: -47.7 ± 34.7, p = 0.012 and fD*: -47.2 ± 48.7, p = 0.040. In comparison, using the bi-exponential IVIM model, only a significant decrease in the parameter fD* was observed for the same regions of interest. In frontal-GM and posterior-GM, the reduction in f and fD* did not reach statistical significance, either with DKI-IVIM or the bi-exponential IVIM model. CONCLUSION: When compared to the bi-exponential IVIM model, the DKI-IVIM model displays a higher sensitivity to detect changes in perfusion induced by the hyperventilation condition.

Breath-hold MR measurements of fat fraction, T1 , and T2 * of water and fat in vertebral bone marrow.

PURPOSE: To assess the feasibility of measuring the fat fraction, T1 and T2 * relaxation times of water and fat signals in vertebral bone marrow using breath-hold magnetic resonance imaging (MRI) gradient echo images of the spine. MATERIALS AND METHODS: MRI experiments were performed at 1.5T on eight healthy volunteers (35.1 ± 15.7 years, five men and three women) using two sagittal four-echo 3D gradient echo volumetric interpolated breath-hold examination (VIBE Dixon) sequences acquired at two different flip angles (5° and 15°). The water/fat decomposition was performed in the vertebral bodies of L1 to L5 by fitting the signal to a function that depends on the echo time and the flip angle to calculate the fat fraction (FF) and T1 and T2 * relaxation times of water and fat signals. Repeatability was assessed by scanning one volunteer six times. RESULTS: The mean fat fraction over L1 to L5 was 33 ± 8%. The mean T1 and T2 * of water and fat signals were respectively T1w = 701 ± 151 msec, T2 *w = 13.7 ± 2.9 msec, T1f = 334 ± 113 msec, and T2 *f = 11.4 ± 2.7 msec. When considering each vertebra separately, the fat fraction increased from L1 to L5 and the T1w decreased from L1 to L5. The mean coefficients of variation obtained from the repeatability study were 8% (FF), 11% (T1w ), 17% (T1f ), 8% (T2 *w ), and 27% (T2 *f ). CONCLUSION: The method introduced in the current study allows for the measurement of the fat fraction and water and fat relaxation times, with a total acquisition time of less than 40 seconds. J. Magn. Reson. Imaging 2016;44:549-555.

Dynamic contrast-enhanced MRI: Study of inter-software accuracy and reproducibility using simulated and clinical data.

PURPOSE: To test the reproducibility and accuracy of pharmacokinetic parameter measurements on five analysis software packages (SPs) for dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), using simulated and clinical data. MATERIALS AND METHODS: This retrospective study was Institutional Review Board-approved. Simulated tissues consisted of pixel clusters of calculated dynamic signal changes for combinations of Tofts model pharmacokinetic parameters (volume transfer constant [K(trans) ], extravascular extracellular volume fraction [ve ]), longitudinal relaxation time (T1 ). The clinical group comprised 27 patients treated for rectal cancer, with 36 3T DCE-MR scans performed between November 2012 and February 2014, including dual-flip-angle T1 mapping and a dynamic postcontrast T1 -weighted, 3D spoiled gradient-echo sequence. The clinical and simulated images were postprocessed with five SPs to measure K(trans) , ve , and the initial area under the gadolinium curve (iAUGC). Modified Bland-Altman analysis was conducted, intraclass correlation coefficients (ICCs) and within-subject coefficients of variation were calculated. RESULTS: Thirty-one examinations from 23 patients were of sufficient technical quality and postprocessed. Measurement errors were observed on the simulated data for all the pharmacokinetic parameters and SPs, with a bias ranging from -0.19 min(-1) to 0.09 min(-1) for K(trans) , -0.15 to 0.01 for ve , and -0.65 to 1.66 mmol.L(-1) .min for iAUGC. The ICC between SPs revealed moderate agreement for the simulated data (K(trans) : 0.50; ve : 0.67; iAUGC: 0.77) and very poor agreement for the clinical data (K(trans) : 0.10; ve : 0.16; iAUGC: 0.21). CONCLUSION: Significant errors were found in the calculated DCE-MRI pharmacokinetic parameters for the perfusion analysis SPs, resulting in poor inter-software reproducibility. J. Magn. Reson. Imaging 2016;43:1288-1300.

Endoluminal high-resolution MR imaging protocol for colon walls analysis in a mouse model of colitis.

OBJECTIVE: An endoluminal magnetic resonance (MR) imaging protocol including the design of an endoluminal coil (EC) was defined for high-spatial-resolution MR imaging of mice gastrointestinal walls at 4.7 T. MATERIALS AND METHODS: A receive-only radiofrequency single-loop coil was developed for mice colon wall imaging. Combined with a specific protocol, the prototype was first characterized in vitro on phantoms and on vegetables. Signal-to-noise ratio (SNR) profiles were compared with a quadrature volume birdcage coil (QVBC). Endoluminal MR imaging protocol combined with the EC was assessed in vivo on mice. RESULTS: The SNR measured close to the coil is significantly higher (10 times and up to 3 mm of the EC center) than the SNR measured with the QVBC. The gain in SNR can be used to reduce the in-plane pixel size up to 39 × 39 µm(2) (234 µm slice thickness) without time penalty. The different colon wall layers can only be distinguished on images acquired with the EC. CONCLUSION: Dedicated EC provides suitable images for the assessment of mice colon wall layers. This proof of concept provides gains in spatial resolution and leads to adequate protocols for the assessment of human colorectal cancer, and can now be used as a new imaging tool for a better understanding of the pathology.

The effect of water suppression on the hepatic lipid quantification, as assessed by the LCModel, in a preclinical and clinical scenario.

OBJECTIVE: To investigate the effect of water suppression on the hepatic lipid quantification, using the LCModel. MATERIALS AND METHODS: MR spectra with and without water suppression were acquired in the liver of mice at 4.7 T and patients at 3 T, and processed with the LCModel. The Cramér-Rao Lower Bound (CRLB) values of the seven lipid resonances were determined to assess the impact of water suppression on hepatic lipid quantification. A paired t test was used for comparison between the CRLBs obtained with and without water suppression. RESULTS: For the preclinical data, in the high (low) fat fraction subset an overall impairment in hepatic lipid quantification, i.e. an increase of CRLBs (no significant change of CRLBs) was observed in spectra acquired with water suppression. For the clinical data, there were no substantial changes in the CRLB with water suppression. Because (1) the water suppression does not overall improve the quantification of the lipid resonances and (2) the MR spectrum without water suppression is always acquired for fat fraction calculation, the optimal data-acquisition strategy for liver MRS is to acquire only the MR spectrum without water suppression. CONCLUSION: For quantification of hepatic lipid resonances, it is advantageous to perform MR spectroscopy without water suppression in a clinical and preclinical scenario (at moderate fields).

Optimization of intra-voxel incoherent motion imaging at 3.0 Tesla for fast liver examination.

BACKGROUND: Optimization of multi b-values MR protocol for fast intra-voxel incoherent motion imaging of the liver at 3.0 Tesla. METHODS: A comparison of four different acquisition protocols were carried out based on estimated IVIM (DSlow , DFast , and f) and ADC-parameters in 25 healthy volunteers. The effects of respiratory gating compared with free breathing acquisition then diffusion gradient scheme (simultaneous or sequential) and finally use of weighted averaging for different b-values were assessed. An optimization study based on Cramer-Rao lower bound theory was then performed to minimize the number of b-values required for a suitable quantification. The duration-optimized protocol was evaluated on 12 patients with chronic liver diseases RESULTS: No significant differences of IVIM parameters were observed between the assessed protocols. Only four b-values (0, 12, 82, and 1310 s.mm(-2) ) were found mandatory to perform a suitable quantification of IVIM parameters. DSlow and DFast significantly decreased between nonadvanced and advanced fibrosis (P < 0.05 and P < 0.01) whereas perfusion fraction and ADC variations were not found to be significant. CONCLUSION: Results showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as DSlow and DFast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis.

ViP MRI: virtual phantom magnetic resonance imaging.

OBJECT: The ability to generate reference signals is of great benefit for quantitation of the magnetic resonance (MR) signal. The aim of the present study was to implement a dedicated experimental set-up to generate MR images of virtual phantoms. MATERIALS AND METHODS: Virtual phantoms of a given shape and signal intensity were designed and the k-space representation was generated. A waveform generator converted the k-space lines into a radiofrequency (RF) signal that was transmitted to the MR scanner bore by a dedicated RF coil. The k-space lines of the virtual phantom were played line-by-line in synchronization with the magnetic resonance imaging data acquisition. RESULTS: Virtual phantoms of complex patterns were reproduced well in MR images without the presence of artifacts. Time-series measurements showed a coefficient of variation below 1% for the signal intensity of the virtual phantoms. An excellent linearity (coefficient of determination r (2) = 0.997 as assessed by linear regression) was observed in the signal intensity of virtual phantoms. CONCLUSION: Virtual phantoms represent an attractive alternative to physical phantoms for providing a reference signal. MR images of virtual phantoms were here generated using a stand-alone, independent unit that can be employed with MR scanners from different vendors.

A microscopic model of the dose distribution in hepatocellular carcinoma after selective internal radiation therapy.

The dosimetry evaluation for the selective internal radiation therapy is currently performed assuming a uniform activity distribution, which is in contrast with literature findings. A 2D microscopic model of the perfused liver was developed to evaluate the effect of two different 90Y microspheres distributions: i) homogeneous partitioning with the microspheres equally distributed in the perfused liver, and ii) tumor-clustered partitioning where the microspheres distribution is inferred from the patient specific images. METHODS: Two subjects diagnosed with liver cancer were included in this study. For each subject, abdominal CT scans acquired prior to the SIRT and post-treatment 90Y positron emission tomography were considered. Two microspheres partitionings were simulated namely homogeneous and tumor-clustered partitioning. The homogeneous and tumor-clustered partitionings were derived starting from CT images. The microspheres radiation is simulated by means of Russell's law. RESULTS: In homogenous simulations, the dose delivery is uniform in the whole liver while in the tumor-clustered simulations a heterogeneous distribution of the delivered dose is visible with higher values in the tumor regions. In addition, in the tumor-clustered simulation, the delivered dose is higher in the viable tumor than in the necrotic tumor, for all patients. In the tumor-clustered case, the dose delivered in the non-tumoral tissue (NTT) was considerably lower than in the perfused liver. CONCLUSIONS: The model proposed here represents a proof-of-concept for personalized dosimetry assessment based on preoperative CT images.

Intravoxel incoherent motion and diffusion kurtosis imaging at 3T MRI: Application to ischemic stroke.

BACKGROUND AND PURPOSE: The DKI-IVIM model that incorporates DKI (diffusional kurtosis imaging) into the IVIM (Intravoxel Incoherent Motion) concept was investigated to assess its utility for both enhanced diffusion characterization and perfusion measurements in ischemic stroke at 3 T. METHODS: Fifteen stroke patients (71 ± 11 years old) were enrolled and DKI-IVIM analysis was performed using 9 b-values from 0 to 1500 s/mm2 chosen with the Cramer-Rao-Lower-Bound optimization approach. Pseudo-diffusion coefficient D*, perfusion fraction f, blood flow-related parameter fD*, the diffusion coefficient D and an additional parameter, the kurtosis, K were determined in the ischemic lesion and controlateral normal tissue based on a region of interest approach. The apparent diffusion coefficient (ADC) and arterial spin labelling (ASL) cerebral blood flow (CBF) parameters were also assessed and parametric maps were obtained for all parameters. RESULTS: Significant differences were observed for all diffusion parameters with a significant decrease for D (p < 0.0001), ADC (p < 0.0001), and a significant increase for K (p < 0.0001) in the ischemic lesions of all patients. f decreased significantly in these regions (p = 0.0002). The fD* increase was not significant (p = 0.56). The same significant differences were found with a motion correction except for fD* (p = 0.47). CBF significantly decreased in the lesions. ADC was significantly positively correlated with D (p < 0.0001) and negatively with K (p = 0.0002); K was also negatively significantly correlated with D (p = 0.01). CONCLUSIONS: DKI-IVIM model enables for simultaneous cerebral perfusion and enhanced diffusion characterization in an acceptable clinically acquisition time for the ischemic stroke diagnosis with the additional kurtosis factor estimation, that may better reflect the microstructure heterogeneity.

MRI image artifact ontology: a proposed method for improved recognition.

UNLABELLED: Magnetic Resonance Imaging is an essential diagnostic imaging technique. The complexity of interpreting MRI images is often compounded by the presence of a wide range of artifacts which are often challenging to identify and eliminate. Ontology permits the construction of a knowledge database with which users can interact given an appropriate interface. The goal of this work is to create an interactive tool for the ontology of MRI artifacts that will allow a radiologist to compare any given MRI artifact image with those contained in the ontology. MATERIAL AND METHOD: Using Protégé 4, we have constructed the ontology with input from an expert in MRI artifacts and utilizing images exemplifying such artifacts. The graphical user interface has been built in Java and the linkage with the ontology made with Owl API. RESULTS: Using the tool, users can compare imaging artifacts encountered in daily practice to those in the database. Once a user has identified the image the most similar to their own, they then have instantaneous access to the knowledge contained in the ontology about the artifact. Individual users can also submit images and have access to DICOM data.