影响短T2成分MR三维超短回波时间双回波脉冲序列成像质量因素的探讨

目的 探讨3D超短回波时间(UTE)舣回波脉冲序列成像的相关成像参数及后处理技术对图像质量的影响.方法 对主要含短T2成分的人于燥股骨标本及一组健康志愿者的胫骨、膝关节、踝部肌腱行MR 3D UTE舣回波脉冲序列成像.通过计算、比较图像的信噪比(SNR)或对比噪声比(CNR)及对图像伪影的分析,探讨系统内部不同轨道延迟时间(-6、-3、-2、-1、0、1、2、3 s)、不同反转角(4°、8°、12°、16°、20°、24°)、不同TE1(0.08、0.16、0.24、0.35 ms)及不同后处理技术(超短回波减影差异图、容积超短回波减影差异图)对图像质量的影响.结果 骨皮质、骨膜、半月板、肌腱、韧带等在UTE图像上表现为高信号.所设的不同轨道延迟时间中,获得最佳SNR的轨道延迟时阳间为2 s.活体人UTE成像的最佳反转角为8°～12°.不同TE1时间的图像质量不同,TE1为0.08 ms时,图像的CNR最佳.随TE1时阳延长,图像伪影逐渐增多.将原始双回波图经多平面重组后再相减(容积超短回波减影差异图),图像SNR明显增加.结论 短T2成分在3D UTE双回波脉冲序列成像上表现为高信号.通过改变反转角和将2次回波图像经MPR后再相减可增加图像SNR.缩短TE1时间可增加图像质量.

Abstract：

Objective To investigate the effect of imaging parameters and postprocessing methods on the quality of MR imaging of short T2 components with 3D ultrashort TE (UTE) double echo pulse sequence. Methods 3D UTE double echo pulse sequence was performed on dry human femoral specimen and the tibial diaphyses, knee joints, and tendons of ankles of a group of healthy volunteers. To investigate the effect of different trajectory delays of the imaging system(-6, -3, -2, - 1,0, 1,2, 3 s), different flip angles(4°, 8°, 12°, 16°, 20°, 24°), different TEs (0. 08, 0. 16, 0. 24, 0. 35 ms)and different postprocessing methods(difference imaging of subtracted volume and non-volume UTE)on the 3D UTE MR imaging quality, the SNR and CNR were calculated and compared, and the artifacts of the images were analysed. Results The cortical bone, periosteum, tendon and meniscus showed high signal intensity on the images of UTE pulse sequence. The best SNR was acquired with 2 s trajectory delay. The best flip angle was 8° to 12° for the human UTE imaging in vivo. The highest CNR was obtained from the TE of 0. 08 ms. The longer the TE was, the more artifacts appeared. The SNR of difference imagewas improved when image subtraction was performed afer multiplanar reconstruction (MPR) of the primary double echo images.Conclusions The short T2 components show high signal intensity on the MRI of 3D UTE double echo pulse sequence. The imaging quality can be improved by shortening TE, using appropriate flip angle and performing subtraction for difference image after MPR of the primary double echo images.     

三维超短回波时间MR成像检测犬肺栓塞的实验性研究

正摘要目的评估自由呼吸状态三维(3D)径向超短回波时间(UTE)MR成像检测肺栓塞(PE)的同时高质量评价肺实质的可行性。材料与方法该研究获得了动物保护委员会的许可。共12只猎兔犬在用自体血凝块诱发肺栓塞前后均进行了MRI及CT检查。在3 T MR进行了屏气3D血管成像及自由呼吸状态3D径向超短回波时间成像(1.0 mm各向同性空间分辨率;回波时间为0.08 ms)。2位放射医师采用盲法将MR血管成像及UTE成像获得的所有肺栓塞进行标记并按     

半月板片状层厚度与多参数超短回波MRI所测压痕刚度的相关性及正常和异常半月板厚度比较

摘要目的确定超短回波(UTE)MRI上半月板片状层厚度与压痕刚度的关系,并比较片状层厚度正常与异常两组之间的MR定量值。方法研究符合HIPAA标准,并经伦理委员会批准。所用的9个半月板来自7例无大体病理结果的志愿者[平均年龄(57.4±14.5)岁],行UTE MR成像并获得T_2、     

利用PET/MR系统超短回波序列检测肿瘤病人的肺小结节

正摘要目的利用混合PET/MR成像系统的自由呼吸式超短回波序列(UTE)评估肿瘤病人的肺小结节,探讨其功用并比较UTE与常用的三维GRE技术对小结节的检出率。材料与方法这一前瞻性研究经HIPAA准许及机构伦理委员会批准。研究组在8例胸腔外恶性肿瘤病人中确诊82个肺内结节。病人在临床PET/CT检查后立即在混合PET/MR成像系统上进行自由呼吸UTE和双回波三维GRE肺成像。CT     

3.0T磁共振乳腺成像扫描参数的优化

目的 探讨不同参数对乳腺MRI图像质量及扫描时间的影响.方法 (1)采用GE Signa Excite 3.0T MR成像系统和8通道乳腺线圈,对3个新鲜手术乳腺标本进行多序列、多参数扫描,根据图像质量及扫描时间选择适合乳腺MR成像的扫描序列和参数.(2)对10名健康志愿者采用FSE-IR、抑脂和非抑脂 FSE-XL T1WI和抑脂FSE-XL T2WI序列及不同参数进行乳腺MR成像,测量比较不同参数图像的信噪比.结果 其它参数相同时,采用以下序列和参数进行乳腺MR成像可在较短的扫描时间内获得较高的图像质量,包括FSE-IR序列:TR 6000 ms、TI 190 ms、TE 42 ms、带宽62.50 kHz、NEX 1、扫描层数18;FSE-XL T1WI序列:TR 500 ms、TE 11.5 ms、带宽50 kHz、NEX 2、扫描层数18;FSE-XL T2WI序列:TR 4200 ms、TE 80 ms、带宽41.67 kHz、NEX 1、扫描层数18.结论 3.0T MR乳腺成像,通过扫描参数的优化可节约扫描时间、提高图像质量.     

正常兔膝关节的三维UTE动态增强MRI实验研究

【摘要】目的：探讨三维超短回波时间（UTE）双回波脉冲序列在主要含短T2成分组织的动态增强MRI中的应用。方法：采用随机数字对照表对6只新西兰大白兔的6个膝关节行MR平扫及UTE动态增强检查。分析正常兔的髌韧带、股骨下段或胫骨上段骨皮质、髓腔的动态增强特点,并与病理结果对照。采用t检验比较未成年兔与成年兔骨皮质的中央管计数。结果：正常兔髌韧带的UTE动态增强信号强度 时间曲线表现为缓慢上升型。未成年兔骨皮质动态增强曲线表现为缓慢上升至峰值时,稍有下降后维持于较高水平;成年兔骨皮质UTE动态增强特点表现为速升速降型。成年兔与未成年兔髓腔的UTE动态增强特点均表现为速升缓降型,组织内对比剂浓度持续较高水平。骨皮质的动态增强曲线差异与组织学所见基本匹配。结论：三维UTE双回波脉冲序列成像可用于主要含短T2成分组织的动态增强检查。     

脊椎关节炎病人的跟腱成像:超声与增强前、后的常规以及短和超短回波时间MRI的比较

目的比较常规、超短回波时间MRI和超声评估脊椎关节炎病人跟腱病变的范围。方法应用MRI和超声研究25例脊椎关节炎并有跟腱症状的病人。静脉注射对比剂前后分别使用T1加权自旋回波、梯度回波和超短回波时间序列(TE选择0.07～16ms)来获得跟腱的MR影像。同时也进行     

MR灌注成像的回波时间和对比剂剂量的选择

目的　研究回波时间 (TE)和对比剂剂量对MR灌注成像 (PWI)的图像质量和计算参数的影响作用 ,确定二者的最适值。方法　 35例健康志愿者 ,分别以TE =2 0、30、4 0ms和 0 1、0 2mmol/kg的钆喷替酸葡甲胺 (Gd DTPA)及TE =30ms、0 3mmol/kg的对比剂行PWI ,观察PWI图像的质量 ,计算脑白质的最大信号强度下降百分率 (SRRmax)和平均通过时间 (MTT)。结果　未用对比剂的PWI图像 ,TE =2 0、30、4 0ms时各组间脑白质信噪比差异有显著意义 (q2 0ms,3 0ms=18 3,q2 0ms,40ms=2 5 9,q3 0ms,40ms=7 5 ,P <0 0 1)。剂量相同或TE相同时各组白质的SRRmax间差异有显著意义 (F0 1mmol/kg=31 5 ,F0 2mmol/kg=131 5 ,F2 0ms=12 1 9,F3 0ms=4 6 9,F40ms=91 4 ,P <0 0 1) ,但MTT间差异无显著意义 (F =0 0 9,P >0 0 5 )。对比剂剂量为 0 3mmol/kg、TE =30ms时与 0 2mmol/kg、TE =30ms方案相比SRRmax差异无显著意义 (F =0 91,P >0 0 5 ) ,而MTT则差异有显著意义 (F =10 2 ,P <0 0 5 )。结论　TE =30ms和 0 2mmol/kg的对比剂剂量 ,可获得最优化的PWI结果     

1.5T MR超短回波三维成像诊断颅骨骨折可行性

正摘要目的探讨MR三维超短回波(3D-UTE)成像诊断颅骨骨折可行性。方法采用CT、UTE和常规MRI扫描10例巴马猪和364例颅脑外伤病人颅骨骨折模型。用ROC曲线、Mc Nemar’s检验和Kappa值分析UTE显示颅骨骨折的准确性。用单因素方差分析和单样本配对t检验对比CT和UTE成像差异以及线性骨折(LF)和凹陷性骨折(DF)解剖值。结果 UTE影像清楚显示颅骨结构和骨折。MR 3D-UTE成像的准确性、有效性及可靠性有优势,与专家阅片无明显差异(P0.05,κ=0.899)。从10个样本中42处线性骨折与13处凹     

超短回波时间MR成像对髌骨的双组分分析:组织病理与偏振光镜结果的关系

摘要目的通过超短回波时间(TE)MR成像,使用半定量组织病理学及偏振光镜(PLM)技术评价人类尸体髌骨软骨,得出短T2*及长T2*水成分的关系。材料与方法得到临床评估委员会同意后,我们使用超短回波时间MR成像、自旋回波成像、组织病理分析及PLM来评估20例人类尸体髌骨。通过对超短-TE信号衰减使用双组分适应,我们分析了每个髌骨短T2*及长T2*水成分。     

Contrast enhancement of short T2 tissues using ultrashort TE (UTE) pulse sequences

AIM: To review the effects of contrast administration on tissues with short T2s using a pulse ultrashort echo time (UTE) sequence. MATERIALS AND METHODS: Pulse sequences were implemented with echo times of 0.08 ms and three later gradient echoes. A fat-suppression option was used and later echo images were subtracted from the first echo image. Contrast enhancement with gadodiamide (0.3 mmol/kg) was used for serial studies in a volunteer. The images of 10 patients were reviewed for evidence of contrast enhancement in short T2 tissues. RESULTS: Contrast enhancement was seen in normal meninges, falx, tendons, ligaments, menisci, periosteum and cortical bone. In addition more extensive enhancement than with conventional pulse sequences was seen in meningeal disease, intervertebral disc disease, periligamentous scar tissue and periosteum after fracture. Subtraction of an image taken with a longer TE from the first image was of value in differentiating enhancement in short T2 tissues from that in long T2 tissues or blood. CONCLUSION: Contrast enhancement can be identified in tissues with short T2s using UTE pulse sequences in health and disease.     

Value of subtraction technique in Gd-DTPA-enhanced magnetic resonance angiography of the thoracic aorta.

AIM: To assess routine image subtraction in 3D gadopentate dimeglumine (Gd-DTPA)-enhanced magnetic resonance (MR) angiography of the thoracic aorta. MATERIALS AND METHODS: This was a prospective study of 22 consecutive patients referred for magnetic resonance imaging (MRI) of the thoracic aorta. All patients had 3D MR aortography (TR/TE/FA; 5/2 ms/25 degrees ) performed before and after bolus intravenous injection of Gd-DTPA. The Gd-DTPA enhanced and unenhanced data sets were subtracted and maximum intensity projections (MIP) projections of the thoracic aorta were performed. The standard unsubtracted MIP images were initially evaluated. These were then reviewed together with the subtracted images to assess for additional diagnostic information. Signal to noise ratios (SNR) and contrast to noise ratios (CNR) were measured. RESULTS: In four cases there was mild image degradation due to patient movement. In no case did subtraction alter the diagnosis. The mean SNR in the unsubtracted MIP images was 10.8 +/- 4.0 (median 11.1) and on the subtracted images was 21.2 +/- 9.9 (median 20.7;P < 0.0001). The mean aorta-to-mediastinal fat CNR was 3.9 +/- 2.8 (median 3.9) on the unsubtracted images and 15.0 +/- 10.6 (median 13) on the subtracted images (P < 0.0001). The mean aorta-to-vertebral body CNR was 5.2 +/- 3.1 (median 4.4) on the unsubtracted images and 15.1 +/- 9.3 on the subtracted images (P < 0.0001). CONCLUSION: Image subtraction significantly improved both the SNR and CNR, but did not alter the final diagnosis, and does not appear warranted in routine practice.     

Centrically reordered inversion recovery half-Fourier single-shot turbo spin-echo sequence: improvement of the image quality of oxygen-enhanced MRI

PURPOSE: The purpose of the study presented here was to determine the improvement in image quality of oxygen-enhanced magnetic resonance (MR) subtraction imaging obtained with a centrically reordered inversion recovery half-Fourier single-shot turbo spin-echo (c-IR-HASTE) sequence compared with that obtained with a conventional sequentially reordered inversion recovery single-shot HASTE (s-IR-HASTE) sequence for pulmonary imaging. MATERIALS AND METHODS: Oxygen-enhanced MR imaging using a 1.5 T whole body scanner was performed on 12 healthy, non-smoking volunteers. Oxygen-enhanced MR images were obtained with the coronal two-dimensional (2D) c-IR-HASTE sequence and 2D s-IR-HASTE sequence combined with respiratory triggering. For a 256x256 matrix, 132 phase-encoding steps were acquired including four steps for phase correction. Inter-echo spacing for each sequence was 4.0 ms. The effective echo time (TE) for c-IR-HASTE was 4.0 ms, and 16 ms for s-IR-HASTE. The inversion time (TI) was 900 ms. To determine the improvement in oxygen-enhanced MR subtraction imaging by c-IR-HASTE, CNRs of subtraction image, overall image quality, and image degradation of the c-IR-HASTE and s-IR-HASTE techniques were statistically compared. RESULTS: CNR, overall image quality, and image degradation of c-IR-HASTE images showed significant improvement compared to those s-IR-HASTE images (P<0.05). CONCLUSION: Centrically reordered inversion recovery half-Fourier single-shot turbo spin-echo (c-IR-HASTE) sequence enhanced the signal from the lung and improved the image quality of oxygen-enhanced MR subtraction imaging.     

Selective water excitation for faster MR imaging of articular cartilage defects: initial clinical results

Our objective was to compare a water-excitation (WE) 3D fast low-angle shot (FLASH) MR sequence for faster imaging of articular cartilage defects of the knee to a conventional fat-saturated (FS) 3D FLASH MR sequence. This prospective study included 16 knees of 16 patients with suspected cartilage lesions. The MR imaging in transverse and sagittal planes included (a) FS 3D FLASH (TR/TE: 45 ms/11 ms, scan time 8 min, flip angle 50°), and (b) WE 3D FLASH (TR/TE: 28 ms/11 ms, scan time 4 min 58 s, flip angle 40°). For each sequence signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were quantified. The detected cartilage lesions were evaluated using a semi-quantitative four-scale scoring system (grades 0–III). The data were compared between the sequences using the paired Student's t-test. No statistically significant differences between the sequences were found for SNR, CNR, and cartilage defect grading (p=0.14–0.8). The WE 3D FLASH MR imaging seems to be promising for fast imaging of articular cartilage lesions of the knee. Electronic Publication     

T2* and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging.

OBJECTIVE: To obtain T2* and proton density measurements of normal human lung parenchyma in vivo using submillisecond echo time (TE) gradient echo (GRE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Six normal volunteers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-holding with acquisition times of 7-16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding measurements of T2* and proton density relative to chest wall muscle. Measurements in supine and prone position were compared, and effects of the level of lung inflation on lung signal were also evaluated. RESULTS: The signal from the lung parenchyma diminished exponentially with prolongation of TE. The measured T2* in six normal volunteers ranged from 0.89 to 2.18 ms (1.43 +/- 0.41 ms, mean +/- S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29 +/- 0.08, mean +/- S.D.). Calculated T2* values of 1.46 +/- 0.50, 1.01 +/- 0.29 and 1.52 +/- 0.18 ms, and calculated relative proton densities of 0.20 +/- 0.03, 0.32 +/- 0.13 and 0.35 +/- 0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior-posterior proton density gradient was reversed in the prone position. There was a pronounced increase in signal from lung parenchyma at maximum expiration compared with maximum inspiration. The ultrashort TE GRE technique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise. CONCLUSION: Quantitative in vivo measurements of lung T2* and relative proton density in conjunction with high-signal parenchymal images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence.     

3D MR sialography protocol for postradiotherapy follow-up of the salivary duct system

PURPOSE: To develop and evaluate an MR sialography protocol that reproducibly images the parotid and submandibular ducts over time, in 3D. Such a protocol is needed in order to investigate the possible radiation-induced changes to the salivary ducts in patients receiving radiotherapy to the head-and-neck. MATERIALS AND METHODS: MR sialography was performed on a 1.5-T MR scanner. Sequence parameters were optimized on 11 healthy volunteers. A 3D water-selective turbo spin echo (TSE) pulse sequence (TR/TE = 6000 msec/190 msec), using a two-element circular surface coil was applied twice in one MR session. In order to assess the reproducibility, the same procedure was repeated four to six months later. The quality of the MR sialograms was measured subjectively by developing a visibility scoring system and objectively by the means of contrast-to-noise ratio (CNR) of the ducts vs. fat (CNR(duct-fat)). RESULTS: High-quality, 3D MR sialographic images were obtained. The quality of the MR sialograms and the subjective visibility score of the salivary ducts were constant over time. The CNR(duct-fat) varied between volunteers (standard deviation, SD 26%) but it was relatively constant per volunteer (SD 5%). CONCLUSION: The MR sialography protocol presented in this study provides good quality 3D imaging of the major salivary ducts, submandibular duct, and the parotid duct and it can be used for the comparison of the salivary duct system of an individual over time.     

Dual-Echo Interleaved Echo-Planar Imaging of the Brain

An interleaved echo-planar imaging (EPI) technique is described that provides images from 20 sections of the brain at two echo times (27 and 84 ms) in 1:05. Six echoes per image per repetition are collected in 24 repetitions of the pulse sequence. MR images of the brain obtained from five volunteers using the dual-echo EPI sequence, fast spin-echo (FSE), and conventional dual-echo spin-echo were evaluated qualitatively for diagnostic use and quantitatively for relative signal-to-noise ratio (SNR), contrast, and contrast-to-noise ratios (CNR).     

Free-breathing renal magnetic resonance angiography with steady-state free-precession and slab-selective spin inversion combined with radial k-space sampling and water-selective excitation.

The impact of radial k-space sampling and water-selective excitation on a novel navigator-gated cardiac-triggered slab-selective inversion prepared 3D steady-state free-precession (SSFP) renal MR angiography (MRA) sequence was investigated. Renal MRA was performed on a 1.5-T MR system using three inversion prepared SSFP approaches: Cartesian (TR/TE: 5.7/2.8 ms, FA: 85 degrees), radial (TR/TE: 5.5/2.7 ms, FA: 85 degrees) SSFP, and radial SSFP combined with water-selective excitation (TR/TE: 9.9/4.9 ms, FA: 85 degrees). Radial data acquisition lead to significantly reduced motion artifacts (P < 0.05). SNR and CNR were best using Cartesian SSFP (P < 0.05). Vessel sharpness and vessel length were comparable in all sequences. The addition of a water-selective excitation could not improve image quality. In conclusion, radial k-space sampling reduces motion artifacts significantly in slab-selective inversion prepared renal MRA, while SNR and CNR are decreased. The addition of water-selective excitation could not improve the lower CNR in radial scanning.     

Sodium imaging optimization under specific absorption rate constraint.

The concept of sodium imaging RF pulse parameter optimization for signal-to-noise ratio (SNR) under specific absorption rate (SAR) constraints is introduced. This optimization concept is unique to sodium imaging, as sodium exhibits ultrarapid T(2) relaxation in vivo, and involves minimizing echo time (TE). For 3D radial k-space acquisition, minimizing TE (and T(2) loss) requires minimizing the RF pulse length. SNR optimization also involves exploiting rapid T(1) relaxation with shortened repetition time (TR) values. However, especially at higher fields, both RF pulse length and TR are constrained by SAR, which is also dependent on the flip angle. Quantum mechanical simulations were performed for SAR equivalent sets of RF pulse length, TR, and flip angle. It was determined that an SNR advantage is associated with a spoiled steady-state approach to sodium imaging with radial acquisition even though significantly longer RF pulses (and TE) are required to implement this approach under the SAR constraint at 4.7T. This advantage, compared to RF pulse sequences implementing ultrashort echo times, 90 degrees flip angles, and longer repetition times, was confirmed in healthy volunteers (measured SNR increase of approximately 38%) and used to produce excellent quality sodium images of the human brain.