T2-weighted MR imaging of focal hepatic lesions: Comparison of various RARE and fat-suppressed spin-echo sequences

The authors prospectively compared four T2-weighted magnetic resonance (MR) sequences, including high-resolution 512 × 512 (matrix size) RARE (rapid acquisition with relaxation enhancement), 256 × 256 RARE, 128 × 256 breath-hold RARE, and 192 × 256 fat-suppressed spin-echo (T2FS) sequences, in the evaluation of 16 patients with focal hepatic masses. MR images were evaluated by quantitative lesion-liver signal difference-to-noise ratios (SDNRs) and subjective evaluation of image artifact and image quality. No significant differences were observed between RARE sequences in SDNR values. The T2FS sequence had a significantly higher SDNR than the 512 × 512 RARE sequence (24.6 ± 15.0 vs 14.5 ± 9.7) (P =.008). Image quality was rated highest for the 512 × 512 RARE and T2FS sequences (P =.006). The inherent advantage of high spatial resolution suggests that the 512 × 512 RARE sequence may be of value in detecting hepatic lesions.     

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

The effect of off-resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatin/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between ±10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a long T₂ relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off-resonance preirradiation. Possible interpretations of these results are discussed.     

Optimization of high-resolution USPIO magnetic resonance imaging at 4.7 T using novel phantom with minimal structural interference

Purpose:

To characterize the effect of ultrasmall superparamagnetic iron oxides (USPIOs) on magnetic resonance imaging (MRI) signal at 4.7 T, and to find the highest sensitivity pulse sequence for high‐resolution USPIO MRI.

Materials and Methods:

A novel phantom was constructed for optimization of sequence parameters for neuroradiological MR applications, and a wide range of dilutions of the USPIO ferumoxtran‐10 was imaged using T₂/T₁‐, T₁‐, T₂‐, T* ₂‐, and PD‐weighted sequences. The effect of varying sequence parameters was investigated using phantom measurements and simulations.

Results:

The relaxivities r₁, r₂, and r*₂ of ferumoxtran‐10 at 4.7 T (21°C) were 5.1, 82.2, and 148.4 mmol^?1 L s^?1, respectively. Gradient echo sequences produced superior susceptibility artifacts at high concentrations; susceptibility artifacts were seen down to a concentration of 137 nmol Fe/mL. A concentration of 17.5 μmol Fe/mL caused a signal void independently of sequence and parameters, and at concentrations ≤273 nmol Fe/mL no signal void was caused. Signal enhancement on T₁‐weighted imaging was seen only at concentrations 137–547 nmol Fe/mL. For the same effective echo time T₂‐weighted rapid acquisition with relaxation enhancement (RARE) yielded significantly higher contrast‐to‐noise ratio with RARE factor 16 than with RARE factor 8.

Conclusion:

At nanomolar concentrations of USPIO, steady‐state free precession offers an alternative to T₂‐ and T* ₂‐weighted sequences. Optimum parameters depend highly on USPIO concentration. J. Magn. Reson. Imaging 2010;32:1184–1196. © 2010 Wiley‐Liss, Inc.

     

Fast imaging of phosphocreatine using a RARE pulse sequence

A technique is described for acquiring phosphocreatine (PCr) images of skeletal muscle using a rapid acquisition with relaxation enhancement (RARE) pulse sequence. All of the phosphorus metabolites other than PCr are forced to dephase within the first few echoes, whereas the Carr-Purcell Mei-boom-Gill (CPMG) pulse sequence maintains a high PCr signal long enough to acquire 64 echoes in a single shot. Axial PCr images of a human forearm with a signal-to-noise ratio of 9 were acquired in 2 min. The effect of the refocusing pulse section profile on the ratio of desired to undesired metabolite signal is demonstrated.     

Phosphocreatine resynthesis during recovery in different muscles of the exercising leg by 31P‐MRS

To investigate the high‐energy phosphate metabolism by ³¹P‐nuclear magnetic resonance spectroscopy during off‐transition of exercise in different muscle groups, such as calf muscles and biceps femoris muscles, seven male long‐distance runners (LDR) and nine untrained males (UT) performed both submaximal constant and incremental exercises. The relative exercise intensity was set at 60% of the maximal work rate (60%Wmax) during both knee flexion and plantar flexion submaximal constant load exercises. The relative areas under the inorganic phosphate (P_i) and phosphocreatine (PCr) peaks were determined. During the 5‐min recovery following the 60%Wmax, the time constant for the PCr off‐kinetics was significantly faster in the plantar flexion (LDR: 17.3 ± 3.6 s, UT: 26.7 ± 6.7 s) than in the knee flexion (LDR: 29.7 ± 4.7 s, UT: 42.7 ± 2.8 s, P < 0.05). In addition, a significantly faster PCr off‐kinetics was observed in LDR than in UT for both exercises. The ratio of P_i to PCr (P_i/PCr) during exercise was significantly lower during the plantar flexion than during the knee flexion (P < 0.01). These findings indicated that the calf muscles had relatively higher potential for oxidative capacity than that of biceps femoris muscles with an association of training status.     

Assessment of 31P relaxation times in the human calf muscle: A comparison between 3 T and 7 T in vivo

Phosphorus (³¹P) T₁ and T₂ relaxation times in the resting human calf muscle were assessed by interleaved, surface coil localized inversion recovery and frequency‐selective spin‐echo at 3 and 7 T. The obtained T₁ (mean ± SD) decreased significantly (P < 0.05) from 3 to 7 T for phosphomonoesters (PME) (8.1 ± 1.7 s to 3.1 ± 0.9 s), phosphodiesters (PDE) (8.6 ± 1.2 s to 6.0 ± 1.1 s), phosphocreatine (PCr) (6.7 ± 0.4 s to 4.0 ± 0.2 s), γ‐NTP (nucleotide triphosphate) (5.5 ± 0.4 s to 3.3 ± 0.2 s), α‐NTP (3.4 ± 0.3 s to 1.8 ± 0.1 s), and β‐NTP (3.9 ± 0.4 s to 1.8 ± 0.1 s), but not for inorganic phosphate (Pi) (6.9 ± 0.6 s to 6.3 ± 1.0 s). The decrease in T₂ was significant for Pi (153 ± 9 ms to 109 ± 17 ms), PDE (414 ± 128 ms to 314 ± 35 ms), PCr (354 ± 16 ms to 217 ± 14 ms), and γ‐NTP (61.9 ± 8.6 ms to 29.0 ± 3.3 ms). This decrease in T₁ with increasing field strength of up to 62% can be explained by the increasing influence of chemical shift anisotropy on relaxation mechanisms and may allow shorter measurements at higher field strengths or up to 62% additional signal‐to‐noise ratio (SNR) per unit time. The fully relaxed SNR increased by +96%, while the linewidth increased from 6.5 ± 1.2 Hz to 11.2 ± 1.9 Hz or +72%. At 7 T ³¹P‐MRS in the human calf muscle offers more than twice as much SNR per unit time in reduced measurement time compared to 3 T. This will facilitate in vivo ³¹P‐MRS of the human muscle at 7 T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Measurement of temperature dependent changes in bone marrow using a rapid chemical shift imaging technique

Purpose:

To provide quantitative temperature monitoring for thermal therapies in bone marrow by measuring temperature‐dependent signal changes in the bone marrow of ex vivo canine femurs heated with a 980‐nm laser at 1.5T and 3.0T.

Materials and Methods:

Using a multi‐gradient echo (≤16) acquisition and signal modeling with the Stieglitz–McBride algorithm, the temperature sensitivity coefficients (TSC, ppm/°C) of water and multiple lipid components' proton resonance frequency (PRF) values are measured at high spatiotemporal resolutions (1.6 × 1.6 × 4 mm³, ≤5 seconds). Responses in R₂* and amplitudes of each peak were also measured as a function of temperature simultaneously.

Results:

Calibrations demonstrate that lipid signal may be used to compensate for B₀ errors to provide accurate temperature readings (<1.0°C). Over a temperature range of 17.2–57.2°C, the TSCs after correction to a bulk methylene reference are ?0.87 × 10^?2 ± 4.7 × 10^?4 ppm/°C and ?0.87 × 10^?2 ± 4.0 × 10^?4 ppm/°C for 1.5T and 3.0T, respectively.

Conclusion:

Overall, we demonstrate that accurate and precise temperature measurements can be made in bone marrow. In addition, the relationship of R₂* and signal amplitudes with respect to temperature are shown to differ significantly where conformal changes are predicted by Arrhenius rate model analysis. J. Magn. Reson. Imaging 2011;33:1128–1135. © 2011 Wiley‐Liss, Inc.

     

Single-shot half-Fourier RARE sequence with ultra-short inter-echo spacing for lung imaging

Purpose

To improve the image quality of pulmonary magnetic resonance (MR) imaging using an ultra‐short inter‐echo spacing half‐Fourier single shot rapid acquisition with relaxation enhancement (USHA‐RARE) sequence.

Materials and Methods

Pulmonary MR images were acquired by USHA‐RARE sequence with various inter‐echo spacings. The sequence parameters were as follows: repetition time (TR)/effective TE: infinite/39–41 msec; section thickness: 10 mm; acquisition matrix: 128 × 128; field of view: 450 × 450 mm. Inter‐echo spacing varied (2.5 msec, 3.0 msec, 3.5 msec, 4.0 msec, 4.5 msec, 5.0 msec), and the respective phase‐encoding steps were 80, 77, 75, 74, 73, and 72. Signal‐to‐noise ratios (SNRs), the signal ratios between lung and fat (lung‐to‐fat ratio: LFRs), and the signal ratios between the lung and the serratus anterior muscle (lung‐to‐muscle ratio: LMRs) of each inter‐echo spacing were calculated, and statistically evaluated.

Results

The SNRs at inter‐echo spacings of ≤ 3.0 msec were significantly higher than those ≥ 4.0 msec (P < 0.05). The LFRs and LMRs at inter‐echo spacing ≤ 3.0 msec were significantly higher than those ≥ 4.0 msec (P < 0.05).

Conclusion

USHA‐RARE sequence does improve signal intensity from the lung. J. Magn. Reson. Imaging 2004;20:336–339. © 2004 Wiley‐Liss, Inc.

     

Magnetically labeled cells can be detected by MR imaging

To determine the feasibility of MR imaging of magnetically labeled cells, different cell lines were labeled with monocrystalline iron oxide (MION) particles. Phantoms containing MION labeled cells were then assembled and imaged by MR at 1.5 T using T1-weighted and T2-weighted pulse sequences. MION uptake ranged from 8.5 × 10⁴ to 2.9 × 10⁵ particles/cell for tumor cells (9L and LX1, respectively) to 1.5 × 10⁶ to 4.8 × 10⁸ particles/cell for “professional phagocytes” (J774 and peritoneal macrophages, respectively). On the T1-weighted images, cell-internalized MION appeared hyperintense relative to agar and similar to MION in aqueous solution. On T2-weighted images, signal intensity varied according to concentration of MION within cells. Cell-internalized MION caused similar MR signal changes of cells as did free MION; however, at a dose that was an order of magnitude lower, depending on the pulse sequence used. The detectability of MION within cells was approximately 2 ng Fe, which corresponded to 10⁵ tumor cells/well or 5 × 10³ macrophages/well. We conclude that a variety of cells can be efficiently labeled with MION by simple incubation. Intracellular labeling may be used for MR imaging of in vivo cell tracking.     

Phosphorus‐31 magnetic resonance spectroscopy of skeletal muscle in maternally inherited diabetes and deafness A3243G mitochondrial mutation carriers

Purpose

To investigate high‐energy phosphate metabolism in striated skeletal muscle of patients with Maternally Inherited Diabetes and Deafness (MIDD) syndrome.

Materials and Methods

In 11 patients with the MIDD mutation (six with diabetes mellitus [DM] and five non‐DM) and eight healthy subjects, phosphocreatine (PCr) and inorganic phosphate (Pi) in the vastus medialis muscle was measured immediately after exercise using ³¹P‐magnetic resonance spectroscopy (MRS). The half‐time of recovery (t1/2) of monoexponentially fitted (PCr+Pi)/PCr was calculated from spectra obtained every 4 seconds after cessation of exercise. A multiple linear regression model was used for statistical analysis.

Results

Patients with the MIDD mutation showed a significantly prolonged t1/2 (PCr+Pi)/PCr after exercise as compared to controls (13.6±3.0 vs. 8.7±1.3 sec, P = 0.01). No association between the presence of DM and t1/2 (PCr + Pi)/PCr was found (P = 0.382).

Conclusion

MIDD patients showed impaired mitochondrial oxidative phosphorylation in skeletal muscle shortly after exercise, irrespective of the presence of DM. J. Magn. Reson. Imaging 2009;29:127–131. © 2008 Wiley‐Liss, Inc.     

Quantification of the 31P metabolite concentration in human skeletal muscle from RARE image intensity.

A method is described for quantifying the cellular phosphorus-31 (31P) concentration in human skeletal muscle based on RARE (rapid acquisition with relaxation enhancement) image intensities. The 31P concentrations were calculated using relaxation rates, RF coil spatial characteristics, and RARE signal intensities from foot muscle and an external 31P standard. 31P RARE and 1H T2-weighted images of the foot muscles in 11 normal subjects were acquired at 3.0 T using a double-tuned (31P/1H) birdcage coil. 31P PRESS (point-resolved spectroscopy) spectra were acquired to verify the measurable 31P concentrations in a multiecho acquisition. The mean measured concentration was 26.4 +/- 3.1 mM (mean +/- SD) from RARE signal intensities averaged over the entire imaged foot anatomy and 27.6 +/- 4.1 mM for a 3 x 3 pixel region-of-interest measurement. The 31P RARE image acquisition time was 4 min with a 0.55 cm3 voxel size. These results demonstrate that the 31P concentration can be accurately measured noninvasively in human muscle from RARE images acquired in short scan times with relatively high spatial resolution.     

Human cardiac high-energy phosphate metabolite concentrations by 1D-resolved NMR spectroscopy

We have developed a method that can measure high-energy phosphate metabolite concentrations in humans with 1D resolved surface-coil NMR spectroscopy. The metabolites are measured by phosphorus (³¹P) NMR spectroscopy, and the tissue water proton (¹H) resonance from the same volume serves as an internal concentration reference. The method requires only the additional acquisition of a ¹H data set, and a simple calibration, performed separately, to determine the ratio of the signal per proton to the signal per phosphorus nucleus. The quantification method is particularly useful for human cardiac spectroscopy, where it eliminates image-based tissue volumetry and the corrections for signal sensitivity and phase nonuniformity necessary in prior approaches. Corrections are introduced to account for blood and fat contributions to the spectra. The method was validated on phantoms of phosphate of varying concentrations and on the human calf muscle. In calf, the adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were 5.6 ± 1.6 (mean ± SD) and 26 ± 4 mmol/kg wet wt, respectively. In normal heart, [ATP] was 5.8 ± 1.6 and [PCr] was 10 ± 2 mmol/kg wet wt. These values are in excellent agreement with prior NMR studies and biopsy data. The protocol is easily accommodated within existing 1D cardiac patient protocols, and the same approach is advantageous for eliminating tissue volumetry and sensitivity corrections when measuring concentrations by 2D and 3D resolved spectroscopy.     

Single-shot diffusion-weighted RARE sequence: Application for temperature monitoring during hyperthermia session

A diffusion-sensitive single-shot RARE (rapid acquisition with relaxation enhancement) sequence was implemented on a 2T whole-body MRI system. The sequence was optimized for diffusion-based MR thermometry, both on a conventional whole-body gradient system and on a high-performance gradient insert. The use of spin-echo versus stimulated-echo diffusion weighting is discussed as a function of gradient performance. Diffusion-based temperature mapping was used to observe the effect of the geometry of the antenna used for radiofrequency (RF) hyperthermia on the temperature distribution. Temperature changes of ±.5°C in gel and ±2°C in a muscle sample in vitro could be detected within 16 seconds (gel) or 1 minute (muscle) at a spatial resolution of 2 × 2 × 8 mm. Temperature changes in vivo were also observed on human muscle cooled with ice with comparable sensitivity for the measured apparent diffusion coefficient (ADC) values.     

Multiband multislice GE‐EPI at 7 tesla,with 16‐fold acceleration using partial parallel imaging with application to high spatial and temporal whole‐brain fMRI

Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k‐space coverage in the phase‐encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4‐fold phase‐encoding undersampling, resulting in 16‐fold acceleration and up to 16‐fold maximal aliasing, was investigated. Task/stimulus‐induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single‐band excitation and longer pulse repetition times. Robust, whole‐brain functional mapping at 7 T, with 2 × 2 × 2mm³ (pulse repetition time 1.25 sec) and 1 × 1 × 2mm³ (pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 × 256 × 176mm³ and 192 × 172 × 176mm³, respectively, was demonstrated with current gradient performance. Magn Reson Med 63:1144–1153, 2010. © 2010 Wiley‐Liss, Inc.     

胶体32P-磷酸铬间质给药对犬累积损伤效应的研究

目的 探讨胶体³²P-磷酸铬(³²P-CP)在正常Beagle犬的肝叶或臀大肌行间质注射的安全性。方法 10只Beagle犬,随机分成间质给药不同剂量(185和370MBq)、不同部位(臀大肌和肝脏)及冷胶体对照5组(n＝2)。术后不同时间点称量体重,行血液生化学检查,ECT轫致辐射显像,组织形态学动态观察及连续测量体表、血液、尿液和粪便放射性计数率值。计量数据以均数±标准差(±s)表示,采用SPSS13.0软件进行统计分析。结果 给药后ECT示肝脏组全肝显影,放射性分布呈团块状不均匀,肌肉组局部放射性持续浓聚,肝脏未见显影。术后第4组犬体重进行性减少,45d时较术前减少2.7kg,余组体重增值均数依序为3.0、1.6、0.8和3.1kg。第4组血小板、红细胞术后有明显减少。分别于给药后23和45d死亡,死亡前谷草转氨酶和谷丙转氨酶均有急剧升高;其余组间血液和血生化学差异无统计学意义。术后体表分区测定以注射部位放射性计数率值为最高,其次为膀胱、脾。肝脏组血液峰时为5min,峰值分别为0.5×10⁷/min和1.0×10⁷/min;肌肉组持续在3×10⁵/min左右。组织学表现肌肉组和肝脏185MBq组4周内有充血水肿改变,8周后组织结构恢复正常;肝脏370MBq组4周内部分肝细胞坏死,6周时见大量肝细胞气球样变,充血水肿明显,肝小叶结构不清。尿液、粪便中放射性计数率肌肉组峰时均数分别为13和12d,峰值为(42.0±3.3)×10⁴/min和(29.6±4.5)×10⁴/min;肝脏组峰时为5和9d,峰值为(49.0±10.2)×10⁴/min和(28.5±7.1)×10⁴/min。至30d肌肉组从尿液和粪便中累积排泄率为36.58%和10.62%,肝脏组为23.48%和8.76%。吸收剂量肝脏组肝脏为(30.6±2.3)、(55.6±4.4)Gy;肌肉组肌肉注射部位为(53.4±3.1)、(98.1±3.3)Gy,肝脏为(2.3±1.3)、(6.5±1.2)Gy。结论 Beagle犬肝脏间质注射794.39MBq/m²,肝脏吸收剂量为56Gy时有较强肝毒性及全身毒副作用,是其致死剂量。肌肉给药463.98～772.93MBq/m²是安全剂量范围。³²P-CP间质给药是适用于治疗凡穿刺所能到达的乏血供及中等血供实体瘤的安全手段。     

3D 23Na MRI of human skeletal muscle at 7 Tesla: initial experience

Objective

To evaluate healthy skeletal muscle pre- and post-exercise via 7 T ²³Na MRI and muscle proton T₂ mapping, and to evaluate diabetic muscle pre- and post-exercise via 7 T ²³Na MRI.

Methods

The calves of seven healthy subjects underwent imaging pre- and post-exercise via 7 T ²³Na MRI (3D fast low angle shot, TR/TE?=?80 ms/0.160 ms, 4 mm?×?4 mm?×?4 mm) and 1 week later by ¹H MRI (multiple spin-echo sequence, TR/TE?=?3,000 ms/15–90 ms). Four type 2 diabetics also participated in the ²³Na MRI protocol. Pre- and post-exercise sodium signal intensity (SI) and proton T₂ relaxation values were measured/calculated for soleus (S), gastrocnemius (G), and a control, tibialis anterior (TA). Two-tailed t tests were performed.

Results

In S/G in healthy subjects post-exercise, sodium SI increased 8–13% (p?<?0.03), then decreased (t _1/2?=?22 min), and ¹H T₂ values increased 12–17% (p?<?0.03), then decreased (t _1/2?=?12–15 min). In TA, no significant changes in sodium SI or ¹H T₂ values were seen (?2.4 to 1%, p?>?0.17). In S/G in diabetics, sodium SI increased 10–11% (p?<?0.04), then decreased (t _1/2?=?27–37 min) without significant change in the TA SI (?3.6%, p?=?0.066).

Conclusion

It is feasible to evaluate skeletal muscle via 3D ²³Na MRI at 7 T. Post-exercise muscle ¹H T₂ values return to baseline more rapidly than sodium SI. Diabetics may demonstrate delayed muscle sodium SI recovery compared with healthy subjects.     

Rapid 3D‐imaging of phosphocreatine recovery kinetics in the human lower leg muscles with compressed sensing

The rate of phosphocreatine (PCr) resynthesis following physical exercise is an accepted index of mitochondrial oxidative metabolism and has been studied extensively with unlocalized ³¹P‐MRS methods and small surface coils. Imaging experiments using volume coils that measure several muscles simultaneously can provide new insights into the variability of muscle function in healthy and diseased states. However, they are limited by long acquisition times relative to the dynamics of PCr recovery. This work focuses on the implementation of a compressed sensing technique to accelerate imaging of PCr resynthesis following physical exercise, using a modified three‐dimensional turbo‐spin‐echo sequence and principal component analysis as sparsifying transform. The compressed sensing technique was initially validated using 2‐fold retrospective undersampling of fully sampled data from four volunteers acquired on a 7T MRI system (voxel size: 1.6 mL, temporal resolution: 24 s), which led to an accurate estimation of the mono‐exponential PCr resynthesis rate constant (mean error <6.4%). Acquisitions with prospective 2‐fold acceleration (temporal resolution: 12 s) demonstrated that three‐dimensional mapping of PCr resynthesis is possible at a temporal resolution that is sufficiently high for characterizing the recovery curve of several muscles in a single measurement. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Temporal and anatomical variations of brain water apparent diffusion coefficient in perinatal cerebral hypoxic-ischemic injury: Relationships to cerebral energy metabolism

Cerebral apparent diffusion coefficients {ADCs) were determined in nine newborn piglets before and for 48 h after transient hypoxia-ischemia. Phosphorus MRS revealed severely reduced cerebral energy metabolism during the insult and an apparently complete recovery 2 h after resuscitation commenced. At this time, mean ADC over the imaging slice (ADC_global) was 0.88 (0.04) × 10^{? 9} m² · s^{? 1} (mean (SD}), which was close to the baseline value of 0.92 (0.4) × 10^{? 9} m² · s^{? 1}. In seven of the animals, a “secondary” failure of energy metabolism then evolved, accompanied by a decline in ADC_global to 0.64 (0.17) × 10^{? 9} m² · s^{? 1} at 46 h postresuscitation (P < 0.001 versus baseline). For these seven animals, ADC_global correlated linearly with the concentration ratio [phosphocreatine (PCr)][inorganic phosphate (Pi)] (0.94 r < 0.99; P > 0.001). A nonlinear relationship was demonstrated between ADC_global, and the concentration ratio [nucleotide triphosphate (NTP)]/ [Pi + PCr + 3 NTP]. The ADC reduction commenced in the parasagittal cortex before spreading in a characteristic pattern throughout the brain. ADC seems to be closely related to cerebral energy status and shows considerable potential for the assessment of hypoxic-ischemic injury in the newborn brain.     

Diffusion-weighted MRI in cystic or necrotic intracranial lesions

Our purpose was to investigate the signal intensities of cystic or necrotic intracranial lesions on diffusion-weighted MRI (DWI) and measure their apparent diffusion coefficients (ADC). We examined 39 cystic or necrotic intracranial lesions in 33 consecutive patients: five malignant gliomas, seven metastases, two other necrotic tumours, a haemangioblastoma, three epidermoids, an arachnoid cyst, seven pyogenic abscesses, 12 cases of cysticercosis and one of radiation necrosis. DWI was performed on a 1.5 T unit using a single-shot echo-planar spin-echo pulse sequence with b 1000 s/mm². The signal intensity of the cystic or necrotic portion on DWI was classified by visual assessment as markedly low (as low as cerebrospinal fluid), slightly lower than, isointense with, and slightly or markedly higher than normal brain parenchyma. ADC were calculated in 31 lesions using a linear estimation method with measurements from b of 0 and 1000 s/mm². The cystic or necrotic portions of all neoplasms (other than two metastases) gave slightly or markedly low signal, with ADC of more than 2.60 × 10⁻³ mm²/s. Two metastases in two patients showed marked high signal, with ADC of 0.50 × 10⁻³ mm²/s and 1.23 × 10⁻³ mm²/s, respectively. Epidermoids showed slight or marked high signal, with ADC of less than 1.03 × 10⁻³ mm²/s. The arachnoid cyst gave markedly low signal, with ADC of 3.00 × 10⁻³ mm²/s. All abscesses showed marked high signal, with ADC below 0.95 × 10⁻³ mm²/s. The cases of cysticercosis showed variable signal intensity; markedly low in five, slightly low in three and markedly high in four. Received: 17 November 1999/Accepted: 3 February 2000     

Fast 31P chemical shift imaging using SSFP methods.

Steady-state free precession (SSFP) methods have been very successful due to their high signal and short imaging times. These properties make them good candidates for applications that intrinsically suffer from low signal such as low gamma nuclei imaging. A new chemical shift imaging (CSI) technique based on the SSFP signal formation has been implemented and applied to (31)P. The signal properties of the SSFP CSI method have been evaluated and the steady-state signal of (31)P has been measured in human muscles. Due to the T(2) and T(1) signal dependence of SSFP, the steady-state signal mainly consists of phosphocreatine (PCr). The technique allows fast CSI acquisitions with high SNR of the PCr signal. The SNR gain for PCr over a FLASH-based CSI method is approx. 4-5. Fast in vivo CSI of human muscle with subcentimeter resolution and high SNR is demonstrated at 2 T.