Suppression of lipid artifacts in amide proton transfer imaging.

Amide proton transfer (APT) imaging is a type of chemical exchange saturation transfer imaging in which the amide protons of cellular proteins and peptides are saturated and detected via the water resonance. To study this effect, conventional magnetization transfer and direct saturation effects in the frequency-dependent water saturation spectrum (z-spectrum) need to be removed by asymmetry analysis with respect to the water frequency offset. When using echo planar imaging, it was found that unequal pericranial fat saturation at equidistant higher and lower frequencies with respect to water leads to a lipid artifact in APT asymmetry images. It is demonstrated that a chemical-shift-selective refocusing pulse in combination with crusher gradients can suppress this artifact and provide high-quality images.     

7 Tesla imaging of cerebral radiation necrosis after arteriovenous malformations treatment using amide proton transfer (APT) imaging

Arteriovenous malformations (AVM) can be treated with stereotactic radiosurgery. An infrequent, but important complication of this treatment is radionecrosis, which can be detected by MRI. However, the imaging characteristics of necrosis are unspecific in conventional MRI. Here, we report a case of necrosis after radiotherapy of an AVM to illustrate the potential of 7 Tesla MRI including amide proton transfer (APT) for necrosis imaging.     

脑小血管病与首次症状性脑出血的相关性MRI研究

目的 回顾性分析首次症状性脑出血(pICH)与脑小血管病(cSVD)的相关关系,以进一步理解脑微出血(CMBs)预测脑出血风险的重要性.方法 收集连续性pICH住院患者202例为研究组,及连续性非脑出血门诊患者234例为对照组.2组患者均行MR检查后,观察并分析CMBs的发病率、部位及分级,以及脑出血的部位、大小.并且对2组的相关cSVD影像表现进行对比分析.用Logistic回归方法对CMBs及脑出血进行相关性分析.同时,对脑出血的大小与CMBs的数量/分级关系进行分析.结果 原发性脑出血组中检出140例(69.3 ％)CMBs,而对照组中检出62例(26.5％).原发性脑出血的CMBs发病率较对照组明显增高(P＜0.000 1).Logistic回归分析结果显示,CMBs是脑出血的相关危险因素,调节OR值为8.363(95％CI 5.210～13.421).脑出血伴CMBs的血肿体积大小为(12.57±17.23) mL,脑出血不伴CMBs的血肿体积大小为(17.77±26.97) mL.脑出血体积大小与CMBs的数量呈负相关关系(rs=-0.176 9,P=0.011 8),与CMBs的分级亦呈负相关关系(rs=-0.118 5,P=0.155 7).结论 CMBs是原发性pICH的独立危险因素,与不同阶段及类型的cSVD相关.     

MR pattern of hyperacute cerebral hemorrhage

Magnetic resonance (MR) pattern of cerebral hemorrhage relates mainly to the relaxation and susceptibility effects of iron-containing hemoglobin degradation products, as well as to their intra- or extracellular location. The purpose of this article is to report two acute stroke patients who underwent thrombolytic therapy and developed hyperacute cerebral hemorrhage during their admission cerebral MR survey. They constitute the earliest MR appearance of hyperacute intracerebral bleeding reported in the literature, featuring increased diffusion properties and persistent susceptibility effect on perfusion-weighted imaging (PWI)-series.     

脑血管淀粉样变性颅内出血的临床及MRI分析

目的:探讨脑血管淀粉样变性脑出血的临床特点及MRI表现,提高对本病的认识及活体诊断水平。方法:对12例经手术病理证实的脑血管淀粉样变性脑出血患者的临床资料与MRI表现进行回顾性分析。12例均行常规T1WI和T2WI检查及磁敏感加权成像(SWI)。结果:12例中,男7例,女5例,年龄47~78岁,平均年龄68岁。临床主要表现为头痛(12例)和脑膜刺激征(7例)。其出血主要位于脑叶的表面,呈分叶状或不规则形,具有多发性和容易复发的特点。常规T1WI和T2WI表现为急性、亚急性和慢性出血灶混合存在,SWI显示为多发性低信号灶。7例合并蛛网膜下腔出血,2例合并脑室出血。结论:脑血管淀粉样变性脑出血在临床和MRI上具有一定的特征,SWI能够提供比常规MRI更加详细、准确的诊断信息,但确诊需要病理学诊断。     

Practical data acquisition method for human brain tumor amide proton transfer (APT) imaging

Amide proton transfer (APT) imaging is a type of chemical exchange–dependent saturation transfer (CEST) magnetic resonance imaging (MRI) in which amide protons of endogenous mobile proteins and peptides in tissue are detected. Initial studies have shown promising results for distinguishing tumor from surrounding brain in patients, but these data were hampered by magnetic field inhomogeneity and a low signal‐to‐noise ratio (SNR). Here a practical six‐offset APT data acquisition scheme is presented that, together with a separately acquired CEST spectrum, can provide B₀‐inhomogeneity corrected human brain APT images of sufficient SNR within a clinically relevant time frame. Data from nine brain tumor patients at 3T shows that APT intensities were significantly higher in the tumor core, as assigned by gadolinium‐enhancement, than in contralateral normal‐appearing white matter (CNAWM) in patients with high‐grade tumors. Conversely, APT intensities in tumor were indistinguishable from CNAWM in patients with low‐grade tumors. In high‐grade tumors, regions of increased APT extended outside of the core into peripheral zones, indicating the potential of this technique for more accurate delineation of the heterogeneous areas of brain cancers. Magn Reson Med 60:842–849, 2008. © 2008 Wiley‐Liss, Inc.     

Detection of hyperacute parenchymal hemorrhage of the brain using echo-planar T2*-weighted and diffusion-weighted MRI

We investigated the usefulness of echo-planar imaging (EPI) as well as T2^*-weighted and diffusion-weighted MRI (DWI) to identify hyperacute hemorrhage (within 24 h after ictus) in the brain. Seven patients were examined 3.5 to 24 h after onset of symptoms using a whole-body 1.5-T MR system. Two diffusion-weighted sequences were run to obtain isotropic and anisotropic diffusion images. Apparent diffusion coefficients (ADC) were calculated from the isotropic diffusion images. All DWI images as well as the T2*-weighted EPI images showed the hematomas as either discrete, deeply hypointense homogeneous lesions, or as lesions of mixed signal intensity containing hypointense areas. We conclude that even in the early phase after hemorrhage, sufficient amounts of paramagnetic deoxyhemoglobin are present in intracerebral hemorrhages to cause hypointensity on EPI T2^*-weighted and DWI images; thus, use of ultrafast EPI allows identification of intracerebral hemorrhage. Received: 21 March 2000 Revised: 26 July 2000 Accepted: 27 July 2000     

Relaxation-compensated fast multislice amide proton transfer (APT) imaging of acute ischemic stroke.

Amide proton transfer (APT) imaging is a variant form of chemical exchange saturation transfer (CEST) imaging that is based on the magnetization exchange between bulk water and labile endogenous amide protons. Given that chemical exchange is pH-dependent, APT imaging has been shown capable of imaging ischemic tissue acidosis, and as such, may serve as a surrogate metabolic imaging marker complementary to perfusion and diffusion MRI. In order for APT imaging to properly diagnose heterogeneous pathologies such as stroke and cancer, fast volumetric APT imaging has to be developed. In this study the evolution of CEST contrast after RF irradiation was solved showing that although the CEST steady state is reached by the apparent longitudinal relaxation rate, the decreases of CEST contrast after irradiation is governed by the intrinsic relaxation constant. A volumetric APT imaging sequence is proposed that acquires multislice images immediately after a single long continuous wave (CW) RF irradiation, wherein the relaxation-induced loss of CEST contrast is compensated for during postprocessing. The proposed technique was verified by numerical simulation, a tissue-like dual-pH phantom, and demonstrated on an embolic stroke animal model. In summary, our study has established a fast volumetric pH-weighted APT imaging technique, allowing further investigation to fully evaluate its diagnostic power.