Longitudinal and multi-echo transverse relaxation times of normal breast tissue at 3 Tesla

Purpose

To measure longitudinal (T₁) and multi‐echo transverse (T₂) relaxation times of healthy breast tissue at 3 Tesla (T).

Materials and Methods

High‐resolution relaxation time measurements were made in six healthy female subjects. Inversion recovery images were acquired at 10 inversion times between 100 ms and 4000 ms, and multiple spin echo images were acquired at 16 echo times between 10 ms and 160 ms.

Results

Longitudinal relaxation times T₁ were measured as 423 ± 12 ms for adipose tissue and 1680 ± 180 ms for fibroglandular tissue. Multi‐echo transverse relaxation times T₂ were measured as 154 ± 9 ms for adipose tissue and 71 ± 6 ms for fibroglandular tissue. Histograms of the voxel‐wise relaxation times and quantitative relaxation time maps are also presented.

Conclusion

T₁ and multi‐echo T₂ relaxation times in normal human breast tissue are reported. These values are useful for pulse sequence design and optimization for 3T breast MRI. Compared with the literature, T₁ values are significantly longer at 3T, suggesting that longer repetition time and inversion time values should be used for similar image contrast. J. Magn. Reson. Imaging 2010;32:982–987. © 2010 Wiley‐Liss, Inc.     

Morphological and biochemical T2 evaluation of cartilage repair tissue based on a hybrid double echo at steady state (DESS‐T2d) approach

Purpose:

To use a new approach which provides, based on the widely used three‐dimensional double‐echo steady‐state (DESS) sequence, in addition to the morphological information, the generation of biochemical T2 maps in one hybrid sequence.

Materials and Methods:

In 50 consecutive MRIs at 3.0 Tesla (T) after matrix‐associated autologous chondrocyte transplantation (MACT) of the knee, by the use this new DESS‐T2d approach, the morphological Magnetic resonance Observation of CArtilage Repair Tissue (MOCART) score, as well as biochemical T2d values were assessed. Furthermore, these results were correlated to standard morphological sequences as well as to standard multi‐echo spin‐echo T2 mapping.

Results:

The MOCART score correlated (Pearson:0.945; P < 0.001) significantly as assessed with standard morphological sequences (68.8 ± 13.2) and the morphological images of the DESS T2d sequence (68.7 ± 12.6). T2 and T2d relaxation times (ms) were comparable in between the control cartilage (T2: 52.5 ± 11.4; T2d: 46.6 ± 10.3) and the repair tissue (T2: 54.4 ± 11.4; T2d: 47.5 ± 13.0) (T2: P = 0.157; T2d: P = 0.589). As expected, T2d values were lower than the standard‐T2 values, however, both functional relaxation times correlated significantly (Pearson:0.429; P < 0.001).

Conclusion:

The presented hybrid approach provides the possibility to combine morphological and biochemical MRI in one fast 3D sequence, and thus, may attract for the clinical use of biochemical MRI. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

NMR properties of human median nerve at 3 T: Proton density,T1, T2, and magnetization transfer

Purpose

To measure the proton density (PD), the T1 and T2 relaxation time, and magnetization transfer (MT) effects in human median nerve at 3 T and to compare them with the corresponding values in muscle.

Materials and Methods

Measurements of the T1 and T2 relaxation time were performed with an inversion recovery and a Carr‐Purcell‐Meiboom‐Gill (CPMG) imaging sequence, respectively. The MT ratio was measured by acquiring two sets of 3D spoiled gradient‐echo images, with and without a Gaussian saturation pulse.

Results

The median nerve T1 was 1410 ± 70 msec. The T2 decay consisted of two components, with average T2 values of 26 ± 2 msec and 96 ± 3 msec and normalized amplitudes of 78 ± 4% and 22 ± 4%, respectively. The dominant component is likely to reflect myelin water and connective tissue, and the less abundant component originates possibly from intra‐axonal water protons. The value of proton density of MRI‐visible protons in median nerve was 81 ± 3% that of muscle. The MT ratio in median nerve (40.3 ± 2.0%) was smaller than in muscle (45.4 ± 0.5%).

Conclusion

MRI‐relevant properties, such as PD, T1 and T2 relaxation time, and MT ratio were measured in human median nerve at 3 T and were in many respects similar to those of muscle. J. Magn. Reson. Imaging 2009;29:982–986. © 2009 Wiley‐Liss, Inc.     

Magnetization transfer‐based 3D visualization of foot peripheral nerves

Purpose:

To investigate magnetization transfer (MT) effects as a new source of contrast for imaging and tracking of peripheral foot nerves.

Materials and Methods:

Two sets of 3D spoiled gradient‐echo images acquired with and without a saturation pulse were used to generate MT ratio (MTR) maps of 260 μm in‐plane resolution for eight volunteers at 3T. Scan parameters were adjusted to minimize signal loss due to T2 dephasing, and a dedicated coil was used to improve the inherently low signal‐to‐noise ratio of small voxels. Resulting MTR values in foot nerves were compared with those in surrounding muscle tissue.

Results:

Average MTR values for muscle (45.5 ± 1.4%) and nerve (21.4 ± 3.1%) were significantly different (P < 0.0001). In general, the difference in MTR values was sufficiently large to allow for intensity‐based segmentation and tracking of foot nerves in individual subjects. This procedure was termed MT‐based 3D visualization.

Conclusion:

The MTR serves as a new source of contrast for imaging of peripheral foot nerves and provides a means for high spatial resolution tracking of these structures. The proposed methodology is directly applicable on standard clinical MR scanners and could be applied to systemic pathologies, such as diabetes. J. Magn. Reson. Imaging 2013;37:1234–1237. © 2012 Wiley Periodicals, Inc.     

T2‐based arterial spin labeling measurements of blood to tissue water transfer in human brain

Purpose:

To investigate blood to tissue water transfer in human brain, in vivo and spatially resolved using a T2‐based arterial spin labeling (ASL) method with 3D readout.

Materials and Methods:

A T2‐ASL method is introduced to measure the water transfer processes between arterial blood and brain tissue based on a 3D‐GRASE (gradient and spin echo) pulsed ASL sequence with multiecho readout. An analytical mathematical model is derived based on the General Kinetic Model, including blood and tissue compartment, T1 and T2 relaxation, and a blood‐to‐tissue transfer term. Data were collected from healthy volunteers on a 3 T system. The mean transfer time parameter T_bl→ex (blood to extravascular compartment transfer time) was derived voxelwise by nonlinear least‐squares fitting.

Results:

Whole‐brain maps of T_bl→ex show stable results in cortical regions, yielding different values depending on the brain region. The mean value across subjects and regions of interest (ROIs) in gray matter was 440 ± 30 msec.

Conclusion:

A novel method to derive whole‐brain maps of blood to tissue water transfer dynamics is demonstrated. It is promising for the investigation of underlying physiological mechanisms and development of diagnostic applications in cerebrovascular diseases. J. Magn. Reson. Imaging 2013;37:332–342. © 2012 Wiley Periodicals, Inc.     

Modulated repetition time look‐locker (MORTLL): A method for rapid high resolution three‐dimensional T1 mapping

Purpose

To demonstrate a modification of the Look‐Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three‐dimensional (3D) balanced steady‐state free precession (b‐SSFP) acquisition (for high signal‐to‐noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization.

Materials and Methods

Two modifications to the Look‐Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b‐SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques.

Results

T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 ± 10 ms, 1202 ± 9 ms, and 4482 ± 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements.

Conclusion

High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin‐echo imaging. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Myocardial T2 quantitation in patients with iron overload at 3 Tesla

Purpose

To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients.

Materials and Methods

A single‐breathhold electrocardiogram‐triggered black‐blood multi‐echo spin‐echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients. Their values, together with the T2* values measured using a breathhold multi‐echo gradient‐echo sequence, were compared with those at 1.5T in the same patients.

Results

At 3T, myocardial T2 was found to be 39.6 ± 7.4 ms in normal subjects. In patients, it ranged from 12.9 to 50.1 ms. T2 and T2* were observed to correlate in heart (ρ = 0.93, ρ < 0.0001) and liver (P = 0.95, P < 0.0001). Myocardial T2 and T2* at 3T were also highly correlated with the 1.5T measurements. Preliminary results indicated that myocardial T2 quantitation was relatively insensitive to B1 variation, and reproducible with 3.2% intra‐exam and 3.8% inter‐exam variations.

Conclusion

Myocardial T2 quantitation is feasible at 3T. Given the substantially decreased T2* and increased B0 inhomogeneity, the rapid myocardial T2 measurement protocol demonstrated here may present a robust alternative to study cardiac iron overload at 3T. J. Magn. Reson. Imaging 2009;30:394–400. © 2009 Wiley‐Liss, Inc.     

Simultaneous temperature and magnetization transfer (MT) monitoring during high‐intensity focused ultrasound (HIFU) treatment: Preliminary investigation on ex vivo porcine muscle

Purpose

To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high‐intensity focused ultrasound (HIFU) treatment.

Materials and Methods

This study proposed an interleaved dual gradient‐echo technique to monitor the heat and tissue damage brought to the heated tissue. The technique was applied to tissue samples to test its efficacy.

Results

Ex vivo experiments on the porcine muscle demonstrated that both temperature changes and MTR exhibited high consistency in localizing the heated regions. As the heat dissipated after the treatment, the temperature of the heated regions decreased rapidly but MTR continued to be elevated. Moreover, thermal dose (TD) maps derived from the temperature curves demonstrated a sharp margin in the heated regions, but MTR maps may show a spatial gradient of tissue damage, suggesting complimentary information provided by these two measures.

Conclusion

In a protocol of spot‐by‐spot heating over a large volume of tissue, MTR provides additional values to mark the locations of previously heated regions. By continuously recording the locations of heated spots, MTR maps could help plan the next target spots appropriately, potentially improving the efficiency of HIFU treatment and reducing undesirable damage to the normal tissue. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Magnetization transfer ratio and volumetric analysis of the brain in macrocephalic patients with neurofibromatosis type 1

The purpose of the study was to evaluate brain myelination by measuring the magnetization transfer ratio (MTR) and to measure grey (GMV) and white matter volume (WMV) in macrocephalic children with neurofibromatosis type 1 (NF1). Seven NF1 patients (aged 0.65–16.67 years) and seven age- and gender-matched controls were studied. A three-dimensional (3D) gradient echo sequence with and without magnetization transfer (MT) prepulse was used for MTR assessment. Volume measurements of GM and WM were performed by applying segmentation techniques on T2-weighted turbo spin echo images (T2WI). MTR of unidentified bright objects (UBOs) on T2WI in cerebellar white matter (52.8±3.3), cerebral peduncles (48.5±1.5), hippocampus (52.6±1.1), internal capsule (55.7±0.3), globus pallidus (52.7±3.9), and periventricular white matter (52.6±1.2) was lower than in the corresponding areas of controls (64.6±2.5, 60.8±1.3, 56.4±0.9, 64.7±1.9, 59.2±2.3, 63.6±1.7, respectively; p<0.05). MTR of normal-appearing brain tissue in patients was not significantly different than in controls. Surface area (mm²) of the corpus callosum (809.1±62.8), GMV (cm³) (850.7±42.9), and white matter volume (WMV) (cm³) (785.1±85.2) were greater in patients than in controls (652.5±52.6 mm², 611.2±92.1 cm³, 622.5±108.7 cm³, respectively; p<0.05). To conclude, macrocephaly in NF1 patients is related to increased GMV and WMV and corpus callosum enlargement. MTR of UBOs is lower than that of normal brain tissue.     

Impact of T2 decay on carotid artery wall thickness measurements

Purpose:

To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness.

Materials and Methods:

The common carotid artery wall was imaged using a spin echo sequence acquired at four echo times (17 ms to 68 ms) in 65 participants as part of VALIDATE study. Images were acquired transverse to the artery 1.5 cm proximal to the flow divider. Mean wall thickness, mean wall signal intensity, lumen area, and outer wall area were measured for each echo. Contours were also traced on the image from the fourth echo and then propagated to the images from the preceding echoes. This was repeated using the image from the first echo. Mean wall signal intensity measurements at the four echo times were fit to a mono‐exponential decay curve to derive the mean T2 relaxation time for each set of contours.

Results:

Mean wall thickness decreased with increasing echo time, with an average thickness reduction of 8.6% between images acquired at the first and last echo times (TE) (0.93 mm at TE 17 ms versus 0.85 mm at TE 68 ms, P < 0.001). Average T2 relaxation time of the carotid wall decreased by 3% when the smaller contours from the last echo were used, which excluded the outer‐most layer (54.3 ± 7.6 ms versus 52.7 ± 6.6 ms, P = 0.03).

Conclusion:

Carotid wall thickness measurements decrease with echo time as expected by the fast T2 relaxation time of the outer‐most layer, namely the adventitia. A short echo time is needed for thickness measurements to include adventitia, which plays an important role in plaque development. J. Magn. Reson. Imaging 2013;37:1493–1498. © 2012 Wiley Periodicals, Inc.     

Non-invasive myocardial iron assessment in thalassaemic patients. T2 relaxometry and magnetization transfer ratio measurements

PURPOSE: To compare T2 relaxometry and magnetization transfer ratio (MTR) measurements of myocardial tissue in normal volunteers and thalassaemic patients for assessment of the myocardial iron levels. MATERIAL AND METHODS: All examinations were done on a 1 T MR system using a multi-echo spin-echo sequence with 8 echoes for T2 measurements and a gradient echo sequence for MTR measurements. Diastolic cardiac triggering was used in both sequences. Ten patients and 10 normal subjects were included in the study. T2 and MTR measurements were correlated with serum ferritin levels. RESULTS: Regression analysis between T2 and MTR measurements and ferritin demonstrated a reversed linear relationship, (r=-0.932, p<0.05) and (r= -0.824, p<0.05), respectively. Mean T2 relaxation time and mean MTR of the normal subjects (57.95+/-4.9 ms and 43.70+/-3.3%) was significantly higher than that of the thalassaemic patients (38.8+/-6.2 ms and 26.40+/-6.1%) (p<0.01), respectively. CONCLUSION: MTR measurements can be used to complement T2 measurements for non-invasive myocardial iron assessment.     

Implementation of vascular‐space‐occupancy MRI at 7T

Vascular‐space‐occupancy (VASO) MRI exploits the difference between blood and tissue T₁ to null blood signal and measure cerebral blood volume changes using the residual tissue signal. VASO imaging is more difficult at higher field because of sensitivity loss due to the convergence of tissue and blood T₁ values and increased contamination from blood‐oxygenation‐level‐dependent (BOLD) effects. In addition, compared to 3T, 7T MRI suffers from increased geometrical distortions, e.g., when using echo‐planar‐imaging, and from increased power deposition, the latter especially problematic for the spin‐echo‐train sequences commonly used for VASO MRI. Third, non‐steady‐state blood spin effects become substantial at 7T when only a head coil is available for radiofrequency transmit. In this study, the magnetization‐transfer‐enhanced‐VASO approach was applied to maximize tissue‐blood signal difference, which boosted signal‐to‐noise ratio by 149% ± 13% (n = 7) compared to VASO. Second, a 3D fast gradient‐echo sequence with low flip‐angle (7°) and short echo‐time (1.8 ms) was used to minimize the BOLD effect and to reduce image distortion and power deposition. Finally, a magnetization‐reset technique was combined with a motion‐sensitized‐driven‐equilibrium approach to suppress three types of non‐steady‐state spins. Our initial functional MRI results in normal human brains at 7T with this optimized VASO sequence showed better signal‐to‐noise ratio than at 3T. Magn Reson Med 69:1003–1013, 2013. © 2012 Wiley Periodicals, Inc.     

Quantitation of brain tissue changes associated with white matter hyperintensities by diffusion‐weighted and magnetization transfer imaging: The LADIS (leukoaraiosis and disability in the elderly) study

Purpose

To explore the value of diffusion‐weighted imaging (DWI) and magnetization transfer imaging (MTI) for the improved detection and quantification of cerebral tissue changes associated with ageing and white matter hyperintensities (WMH).

Materials and Methods

DWI (n = 340) and MTI (n = 177) were performed in nine centers of the multinational Leukoaraiosis And DISability (LADIS) study investigating the impact of WMH on 65‐ to 85‐year‐old individuals without prior disability. We assessed the apparent diffusion coefficient (ADC) and magnetization transfer ratio (MTR) of normal appearing brain tissue (NABT) and within WMH and related them to subjects' age and WHM severity according to the Fazekas score.

Results

ADC and MTR values showed a significant inter‐site variation, which was stronger for the MTR. After z‐transformation multiple regression analysis revealed WMH severity and age as significant predictors of global ADC and MTR changes. Only lesional ADC, but not MTR was related to WMH severity.

Conclusion

ADC and MTR are both sensitive for age and WMH related changes in NABT. The ADC is more sensitive for tissue changes within WMH and appears to be more robust for multicenter settings. J. Magn. Reson. Imaging 2009;29:268–274. © 2009 Wiley‐Liss, Inc.     

Aging effects on human calf muscle properties assessed by MRI at 3 Tesla

Purpose

To determine age‐related changes in MR properties as T2 and T2* relaxation times, fat content, and magnetization transfer in the human calf, and comparison of these effects in different muscle groups.

Materials and Methods

Studies were performed on 12 “younger” (mean, 31.2 ± 6.1 years) and 11 “older” healthy adult individuals (mean, 66.1 ± 7.8 years). The tibialis anterior muscle, the soleus muscle and the gastrocnemius muscle were examined at rest in a 3 Tesla whole‐body MR unit. T2 and T2*, muscular fat content and magnetization transfer ratios (MTR) were determined. Results of the two age groups were compared, and differences between the muscle groups were investigated.

Results

Increase of T2 and muscular fat was detected with age with significant difference between the age groups. The extent of fatty infiltration was much more variable for the “older” group. For both age groups, the tibialis anterior muscle showed the lowest fat content with 1.2 ± 0.4% in the “young” group and 2.3 ± 0.7% in the “older” group. A strong correlation between fat content and T2 was found, while the groups did not significantly differ regarding T2*. Decrease in the MTR could only be shown for the tibialis anterior muscle with age.

Conclusion

Age‐related changes in healthy human calf musculature were found. Further studies might show possible correlations of age‐dependent changes with physical efficiency and susceptibility to diseases like type 2 diabetes. J. Magn. Reson. Imaging 2009;29:1346–1354. © 2009 Wiley‐Liss, Inc.     

Is the magnetization transfer ratio a marker for myelin in multiple sclerosis?

Purpose

To investigate the correlation between water content (WC) and magnetization transfer ratio (MTR) in normal and multiple sclerosis (MS) brain. The MTR has been proposed as a marker for myelin in central nervous system tissue. However, changes in WC due to inflammation and edema may also affect the MTR.

Materials and Methods

Seven MS subjects with active disease and seven age‐ and gender‐matched controls were scanned using quantitative magnetic resonance techniques. WC, myelin water content, T₁ relaxation time, and MTR were calculated from areas of lesion (divided into new lesions less than 2 months old, isointense T₁ lesions, and hypointense T₁ lesions), contralateral normal‐appearing white matter (NAWM), and location‐matched normal white matter (NWM) in controls. Linear regression was used to determine the correlation between WC and MTR.

Results

A significant correlation was found between WC and MTR across all tissue (R = ?0.65, P < 0.0005).

Conclusion

MTR was correlated with WC in MS tissue, indicating that inflammation and edema influence MTR. Therefore, caution should be used when associating MTR exclusively with myelin content. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Development of a novel optimized breathhold technique for myocardial T2 measurement in thalassemia

Purpose

To develop a reproducible fast spin‐echo (FSE) technique for accurate myocardial T2 measurement with application to iron overload assessment in thalassemia.

Materials and Methods

An FSE sequence was developed to permit acquisition of multiple TE images in one breathhold (BH‐FSE). A dynamic black‐blood scheme was introduced to better cancel blood signal. A nonselective refocusing train was also adopted to suppress stimulated echoes. The optimized technique was tested on phantoms and then applied to 10 normal volunteers and 10 thalassemia patients. Interstudy reproducibility was measured on all the 20 subjects.

Results

The mean difference in T2 values was 1.7% from phantom experiments between BH‐FSE and the conventional spin‐echo (SE) technique. High contrast BH‐FSE images were acquired from human subjects, with minimal stimulated echoes and effective blood suppression (P = 0.0005). The coefficient of variation for interstudy reproducibility was 4.3%. T2 values from thalassemia patients were substantially lower than those from the normal subjects (45.2 ± 26.1 msec vs. 56.9 ± 8.4ms, P = 0.02).

Conclusion

The dynamic black‐blood T2 sequence is a fast reproducible acquisition that compares favorably with conventional techniques, is robust to motion artifacts, and yields high blood‐myocardium contrast. This technique may provide a useful tool in thalassemia and other scenarios requiring myocardial T2 quantification. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

Potential of magnetization transfer MRI for target volume definition in patients with non‐small‐cell lung cancer

Purpose

To develop a magnetization transfer (MT) module in conjunction with a single‐shot MRI readout technique and to investigate the MT phenomenon in non‐small‐cell lung cancer (NSCLC) as an adjunct for radiation therapy planning.

Materials and Methods

A total of 10 patients with inoperable NSCLC were investigated using a 1.5T MR scanner. MT ratio (MTR) maps of several slices throughout the tumor were assessed. Each MTR‐map was acquired within a short breathhold. Fluorodeoxyglucose positron emission tomography (FDG‐PET) investigations were performed in addition to the MRI protocol. A total of 60 structures appearing conspicuous in FDG‐PET were compared with structures appearing conspicuous in corresponding MTR maps. Quantification of similarity between both modalities was performed using similarity index calculation.

Results

MTR‐maps showed different contrast than FDG‐PET images. However, structures that appeared conspicuous in FDG‐PET images, either by a marked signal enhancement or signal decrease, were found to be similarly present in MTR maps. A mean similarity index of 0.65 was calculated. MTR values of suspected atelectasis were on average lower than MTR values of tumor tissue.

Conclusion

The proposed MT‐MRI technique provides a high MT efficiency, while being robust and fast enough for breathhold acquisition. The results obtained encourage for further exploration of MT‐MRI as an adjunct for radiotherapy planning in NSCLC. J. Magn. Reson. Imaging 2008;28:1417–1424. © 2008 Wiley‐Liss, Inc.     

Quantitative evaluation of liver cirrhosis using T1 relaxation time with 3 tesla MRI before and after oxygen inhalation

Purpose:

To quantify liver T1 relaxation times before and after oxygen inhalation in patients with and without liver cirrhosis using a 3 Tesla (T) MRI.

Materials and Methods:

Institutional Review Board approval and written informed consent were obtained. Ninety‐two noncirrhotic patients and 87 patients with hepatitis B viral liver cirrhosis (72 Child‐Pugh class A and 15 Child‐Pugh class B or C) underwent MRI with a 3.0T system before and after the supply of 100% oxygen at a rate of 15 L/min by means of a nonrebreather ventilation mask for 3 min. T1 maps were acquired using three‐dimensional spoiled gradient echo sequences with two different flip angles (2° and 14°) and a fixed TR/TE (2.54 ms/0.95 ms). Liver T1 values were obtained using a T1 processing tool (MapIT software). The mean baseline T1 values of three groups (control, Child‐Pugh class A, and Child‐Pugh class B/C) were compared using an analysis of variance test. Liver T1 value before and after oxygenation was compared using a paired t‐test for each group.

Results:

The baseline liver T1 value was significantly higher in the control group (941 ± 136 ms) than in Child‐Pugh A (858 ± 143 ms) and Child‐Pugh B/C (783 ± 164 ms) group (P < 0.001 and P < 0.0001). The reduction in the liver T1 value after oxygen inhalation was significant in the control group (P = 0.012) but not significant in Child‐Pugh class A (P = 0.079) and Child‐Pugh class B/C (P = 0.752).

Conclusion:

The baseline liver T1 relaxation time was significantly different between the patients with and without liver cirrhosis. The shortening effect of oxygen on the liver T1 value was significant in the control group but not in the cirrhotic patients. J. Magn. Reson. Imaging 2012;36:405–410. © 2012 Wiley Periodicals, Inc.     

Model-based nonlinear inverse reconstruction for T2 mapping using highly undersampled spin-echo MRI

Purpose:

To develop a model‐based reconstruction technique for T2 mapping based on multi‐echo spin‐echo MRI sequences with highly undersampled Cartesian data encoding.

Materials and Methods:

The proposed technique relies on a nonlinear inverse reconstruction algorithm which directly estimates a T2 and spin‐density map from a train of undersampled spin echoes. The method is applicable to acquisitions with single receiver coils but benefits from multi‐element coil arrays. The algorithm is validated for trains of 16 spin echoes with a spacing of 10 to 12 ms using numerical simulations as well as human brain MRI at 3 Tesla (T).

Results:

When compared with a standard T2 fitting procedure using fully sampled T2‐weighted images, and depending on the available signal‐to‐noise ratio and number of coil elements, model‐based nonlinear inverse reconstructions for both simulated and in vivo MRI data yield accurate T2 estimates for undersampling factors of 5 to 10.

Conclusion:

This work describes a promising strategy for T2‐weighted MRI that simultaneously offers accurate T2 relaxation times and properly T2‐weighted images at arbitrary echo times. For a standard spin‐echo MRI sequence with Cartesian encoding, the method allows for a much higher degree of undersampling than obtainable by conventional parallel imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Short TE 7Li‐MRS confirms Bi‐exponential lithium T2 relaxation in humans and clearly delineates two patient subtypes

Purpose:

(i) To develop an MRS technique to measure ⁷Li levels in human brain in a reasonable scan time, (ii) to develop a technique to quantify ⁷Li T2 relaxation times as measured from human brain in patients taking lithium for the treatment of their bipolar disorder, and (iii) to confirm or refute the presence of bi‐exponential ⁷Li T2 relaxation in human brain.

Materials and Methods:

We modified a spin‐echo MRS pulse sequence to decrease its minimum echo time. With IRB approval, we performed lithium MRS with the modified pulse sequence on 13 euthymic bipolar patients stable on long‐term lithium to treat their disease.

Results:

We were able to achieve a total scan time per sample of 8:20; total scan time including imaging, calibration and MRS was approximately 1 h 15 min. We observed bi‐exponential T2 relaxation in the majority of patients, with an average short decay time of 5.3 ± 1.4 ms and an average long decay time of 68.2 ± 10.2 ms. However, in two patients we observed strongly mono‐exponential T2 relaxation with an average decay time of 47.4 ± 1.3 ms.

Conclusion:

⁷Li relaxation patterns may prove useful to distinguish between lithium‐responsive and lithium nonresponsive bipolar patients. J. Magn. Reson. Imaging 2013;37:1451–1459. © 2012 Wiley Periodicals, Inc.