Array compression for MRI with large coil arrays.

Arrays with large numbers of independent coil elements are becoming increasingly available as they provide increased signal-to-noise ratios (SNRs) and improved parallel imaging performance. Processing of data from a large set of independent receive channels is, however, associated with an increased memory and computational load in reconstruction. This work addresses this problem by introducing coil array compression. The method allows one to reduce the number of datasets from independent channels by combining all or partial sets in the time domain prior to image reconstruction. It is demonstrated that array compression can be very effective depending on the size of the region of interest (ROI). Based on 2D in vivo data obtained with a 32-element phased-array coil in the heart, it is shown that the number of channels can be compressed to as few as four with only 0.3% SNR loss in an ROI encompassing the heart. With twofold parallel imaging, only a 2% loss in SNR occurred using the same compression factor.     

Optimization of localized 19F magnetic resonance spectroscopy for the detection of fluorinated drugs in the human liver.

Fluorine MR spectroscopy ((19)F MRS) is an indispensable tool for assessing the pharmacokinetics of fluorinated drugs. Since the metabolism of 5-fluorouracil (5FU), a frequently used cytotoxic drug, is expected to be different in normal liver and in tumor tissue, spatial localization is required for detection by MRS. In this study, three independent signal-to-noise ratio (SNR) optimizations were combined to enable chemical shift imaging (CSI) as a localization method in the detection of 5FU and its metabolites in tumor tissue. First, the hardware was optimized by using circularly polarized coils together with integrated preamplifiers. Second, the optimal pulse angle (Ernst angle) was determined on the basis of T(1) relaxation time measurements of 5FU. Finally, averaging of CSI phase-encoding steps was optimized by using the applied Hamming filter as a weighting function. The combination of these three methods enables the in vivo detection of 5FU and alpha-fluoro-beta-alanine (FBAL) by (19)F MRS, localized in three dimensions in tumor and liver tissue at a time resolution of 4 min at 1.5 Tesla.     

电解可脱式微弹簧圈栓塞治疗颅内动脉瘤

目的　探讨电解可脱式微弹簧圈 (GDC)栓塞治疗颅内动脉瘤的方法。方法　采用美国波士顿公司GDC栓塞治疗 1 7例患者中 1 8个颅内动脉瘤 ,其中 1 5例蛛网膜下腔出血 (SAH)发病者 ,术前Hunt和Hess分级 :Ⅰ～Ⅱ级1 0例 ;Ⅲ级 3例 ;Ⅳ级 2例。结果　 1例死亡 ,3例轻度短期神经功能障碍 ,1 3例痊愈。结论　GDC栓塞治疗颅内动脉瘤较为理想 ,但还需随访观察     

眼球孤立性脉络膜血管瘤的HR-MRI表现

目的　探讨眼球孤立性脉络膜血管瘤的高分辨率磁共振 (HR MRI)影像学特征 ,进一步提高诊断水平。资料与方法　回顾性分析诊断明确的孤立性脉络膜血管瘤 16例共计 17个病灶的位置、数目、形态、大小、MRI信号、强化情况、有无合并视网膜脱离及有无视神经和眼外侵犯等。所有病例均行HR MRI及增强扫描 ,部分病例行脂肪抑制。结果　 17个病灶中的 16个呈扁丘状位于眼球内壁的后极。 15个病灶厚度 <5mm ,平均厚度为2 .9mm。病灶边缘清晰 ,T1WI上呈轻度高信号者 16个 ,T2 WI上呈等信号者 15个 ,增强扫描显著强化者有 12个。 3例合并视网膜脱离 ,在T2 WI上多呈等信号 ,T1WI上呈轻度高信号者 ,均无强化。无视神经及眼外侵犯病例。结论　 94 %孤立性脉络膜血管瘤的HR MRI表现具有特征性 ,表现为位于眼球内壁后极的较小、基底较宽、边缘清晰的扁丘状病灶。其T1WI信号高于玻璃体 ,T2 WI信号等于玻璃体 ,增强扫描瘤体显著强化。明确其HR MRI影像学特征有助于临床与恶性葡萄膜黑色素瘤相鉴别 ,避免不必要的眼球摘除     

Whole-brain 3D perfusion MRI at 3.0 T using CASL with a separate labeling coil.

A variety of continuous and pulsed arterial spin labeling (ASL) perfusion MRI techniques have been demonstrated in recent years. One of the reasons these methods are still not routinely used is the limited extent of the imaging region. Of the ASL methods proposed to date, continuous ASL (CASL) with a separate labeling coil is particularly attractive for whole-brain studies at high fields. This approach can provide an increased signal-to-noise ratio (SNR) in perfusion images because there are no magnetization transfer (MT) effects, and lessen concerns regarding RF power deposition at high field because it uses a local labeling coil. In this work, we demonstrate CASL whole-brain quantitative perfusion imaging at 3.0 T using a combination of strategies: 3D volume acquisition, background tissue signal suppression, and a separate labeling coil. The results show that this approach can be used to acquire perfusion images in all brain regions with good sensitivity. Further, it is shown that the method can be performed safely on humans without exceeding the current RF power deposition limits. The current method can be extended to higher fields, and further improved by the use of multiple receiver coils and parallel imaging techniques to reduce scan time or provide increased resolution.     

眶骨的改变在眶部疾病HR-MRI诊断中的作用

目的:探讨眶骨的影像学所见及其在眶部疾病诊断中的作用。方法:回顾性分析诊断明确的眶部疾病80例的HR-MRI影像表现。80例中良性囊肿18例，外伤6例，炎性疾病6例，蝶骨嵴脑膜瘤9例，其他肿瘤41例。磁共振扫描采用1．5T GE Signa及Siemens Magnetom Sp63磁共振扫描机，用眶部表面线圈，SE系列常规轴位、冠状位及矢状位扫描，部分病例行脂肪抑制及增强扫描。结果：正常眶骨的HR-MRI表现为结构完整，边缘光整，皮质骨在T1WI及。T2WI上均为无信号区。15例眶骨受压迫性改变全见于良性囊肿的病例，骨质增生改变主要见于蝶骨脑膜瘤，2例骨折见于外伤病例，21例骨质破坏大多见于不同的恶性肿瘤病变中。结论：不同的眶部病变对眶骨的影响有差异，良性囊肿主要表现为眶骨受压迫性改变，蝶骨脑膜瘤多表现为骨质增生，外伤病例伴有眶骨骨折，恶性肿瘤病例常伴有眶骨的破坏。眶骨的改变对眶部疾病HR-MRI的诊断和鉴别诊断有重要作用。     

颅内后循环远端动脉瘤的介入治疗

目的回顾性分析20例以电熔断解脱弹簧圈栓塞的后循环远端动脉瘤的治疗结果,探讨颅内动脉后循环远端动脉瘤的介入治疗方法与安全性。方法20例患者(其中18例以自发性蛛网膜下腔出血起病,2例以头痛起病)经造影证实大脑后动脉、小脑上动脉、小脑前下动脉、小脑后下动脉之远端动脉瘤分别为2例、4例、4例、10例。其中小脑上动脉供血之动静脉畸形1例,伴有血流相关破裂动脉瘤。小脑后下动脉远端多发动脉瘤1例。所有动脉瘤均采用GDC、EDC或Matrix弹簧圈栓塞。其中单纯栓塞动脉瘤2例;栓塞动脉瘤同时栓塞载瘤动脉18例。结果所有病例栓塞操作均顺利完成,无手术相关的死亡,术后出现一过性功能障碍2例;载瘤动脉栓塞后多数可见侧支供血,未见叫显的小脑供血减少。结论后循环远端动脉瘤由于动脉瘤特性、载瘤动脉细小、动脉瘤与载瘤动脉比例等因素,多需要闭塞载瘤动脉。为避免可能造成的侧支血管的闭塞,建议用弹簧圈栓塞。     

Eight-channel transmit/receive body MRI coil at 3T.

Multichannel transmit magnetic resonance imaging (MR) systems have the potential to compensate for signal-intensity variations occurring at higher field strengths due to wave propagation effects in tissue. Methods such as RF shimming and local excitation in combination with parallel transmission can be applied to compensate for these effects. Moreover, parallel transmission can be applied to ease the excitation of arbitrarily shaped magnetization patterns. The implementation of these methods adds new requirements in terms of MRI hardware. This article describes the design of a decoupled eight-element transmit/receive body coil for 3T. The setup of the coil is explained, starting with standard single-channel resonators. Special focus is placed on the decoupling of the elements to obtain independent RF resonators. After a brief discussion of the underlying theory, the properties and limitations of the coil are outlined. Finally, the functionality and capabilities of the coil are demonstrated using RF measurements as well as MRI sequences.     

Transceive surface coil array for MRI of the human prostate at 4T.

A novel torso transceive surface coil array for prostate magnetic resonance imaging (MRI) and spectroscopy (MRS) at 4T is presented. It is shown that with the use of a conformal transceive surface coil array with 50 Omega transmitter amplifiers and receiver preamplifiers, one can perform whole-volume torso imaging while maintaining the high signal-to-noise ratio (SNR) inherent to surface coil designs. Recent theoretical considerations have shown that by focusing the infringing radiofrequency (RF) electromagnetic field, one can achieve increased penetration and signal homogeneity compared to a conventional circularly polarized driving scheme. A variation of this driving scheme particular to the proposed coil design resulted in a twofold increase in SNR in the prostate compared to that achieved with a conventional circularly polarized driving scheme. The novel transceive surface coil array presented is capable of full-volume imaging of the human torso at 4T while maintaining signal penetration in the deep region of the prostate gland.     

体部表面线圈磁共振成像对肛瘘的术前诊断价值

目的:探讨体部表面线圈MRI对肛瘘的术前诊断价值。材料和方法:回顾性分析42例肛瘘患者,均于术前进行非增强MRI检查,将MRI结果与手术结果对照。结果:MRI诊断结果与手术结果一致,其中23例为括约肌间型,5例经括约肌型,5例括约肌上型,9例括约肌外型,所有病例中有12例可见肛周脓肿形成。结论:MRI作为一种安全、准确的肛瘘检查方法,对于肛瘘的术前诊断具有非常重要的价值。