自动移床3D CES MRA在下肢动脉检查中的初步应用

目的：探讨自动移床3维增强减影MR血管造影(3DCES MRA)在下肢动脉疾病检查中的应用价值。方法：16例临床怀疑下肢动脉性病变者进行了自动移床3D CES MRA认检查，原始图像经减影后作最大密度投影(MIP)重建。结果：所有病例的血管均显示满意，其中11例可见不同部位和分支动脉狭窄或闭塞，阳性诊断率为68．7％。结论：初步结果表明，自动移床3D CES MRA检查技术对下肢动脉病变有重要诊断价值。     

Interventional MR angiography with a floating table

A floating table was integrated into a setup for performance of interventional magnetic resonance (MR) angiography procedures with actively visualized catheters and biplanar real-time image fusion. The setup was evaluated by performing catheterizations in eight pigs. The floating table enabled the authors to follow actively visualized instruments in the pigs' vasculature during MR imaging-guided interventional angiography procedures while performing real-time biplanar MR imaging. Interventional MR angiography with a floating table enables the field of view to be moved along with the instrument tip to the region of interest and thus enhances the usability and flexibility of the interventional MR imaging setup.     

Conventional MRA and contrast- enhanced MRA of extracranial vessel segments

Summary The introduction of fast gradient systems allows a reliable visualization of the extracranial carotid vessels by the magnetic resonance angiography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF) technique, vessels can be imaged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences, the first-pass evaluation of an intravenous bolus-injection of Gadolinium in the carotids from the aortic arch up to the skull base can be performed in less than 30 s. In this study, advantages and disadvantages of both techniques are discussed. For a qualitatively optimal contrast enhanced MRA (CE-MRA) timing parameters like injection delay, flow rate and the adjustment of sequence parameters have to be considered in relation to the fast venous return from the sinus to the jugular veins. First, the optimal time point of the data acquisition have been determined at a model and with a computer simulation in reference to the presence of CA in the arteries. As a result, 90 % of the contrast contribution is defined by 16 % of the symmetrically acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution, measuring time and CA-injection parameters and was proved in normal volunteers and patients. An exact determination of the bolus-arrival-time by means of a test-bolus injection was acquired. The best qualitative results were achieved by a double-dose injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in the improvement of the spatial resolution. To date, further investigations related to the problem of optimal CA-application may improve the potentials of CE-MRA procedures.      

动态增强MRA的临床研究

目的与常规ＭＲＡ比较，并以手术或ＤＳＡ作为金标准，评估动态增强磁共振血管成像（ＤＣＥＭＲＡ）的图像质量和应用价值。方法４０例共１３２条体部血管同时作了常规ＭＲＡ和ＤＣＥＭＲＡ检查，前者以二维时间飞跃法（２ＤＴＯＦ）ＭＲＡ为主，后者以三维（３Ｄ）ＤＣＥＭＲＡ为主，部分病例屏气扫描（２０～３０秒），快速注射ＧｄＤＴＰＡ２０ｍｌ（０．１５～０．２ｍｍｏｌ／ｋｇ），造影剂注射速度和扫描时间依据靶血管的性质、部位、范围而定。结果４０例中３５例发现有血管病变，与手术或其他影像学方法检查结果一致。３０例主动脉弓及弓上分支、腹主动脉、腔静脉及门静脉的显示满意率，２ＤＴＯＦＭＲＡ为４０％，ＤＣＥＭＲＡ为９６％，颈动脉及下肢血管则分别为９０％、７０％。利用配对计数资料χ２检验，前者两种方法有显著性差异（χ２＝１６．６５，Ｐ＜０．００１），后者无显著性差异（精确卡方检验：χ２＝０．５８，Ｐ＞０．０５）。结论ＤＣＥＭＲＡ为新的磁共振血管成像技术，克服了常规ＭＲＡ的许多缺点，尤其对胸腹部血管，两种方法血管显示满意率有极显著性差异。屏气薄层３ＤＤＣＥＭＲＡ技术，几乎达到与ＤＳＡ相仿的结果，其临床应用潜能极大。     

Fully automated floating table MR angiography of pelvic and leg arteries: initial clinical results]

The aim of this study was to obtain first clinical experiences with magnetic resonance angiography (MRA) with digital subtraction (MR-DSA) using an automatic floating table for visualization peripheral arteriosclerotic occlusive disease (paod). We examined 10 patients on a 1.5 T MR unit applying a fast MRA technique (3D FLASH) with intravenous application of positive contrast agent. MR-DSA examinations were compared with the gold standard intraarterial (i.a.) DSA. MR-DSA proved to be useful for routine application which could be performed sufficiently in all patients. MR-DSA and i.a. DSA showed comparable results for imaging of the pelvic and upper leg arteries. Looking at the thighs image quality of MR-DSA did not match the image quality of i.a. DSA in every case. This was due to venous overlap and in comparison to i.a. DSA reduced signal-to-noise ratios. However, clinical findings, obtained with MR-DSA, were sufficient for adequate therapy planning. Our preliminary results reveal the potential of this new technique to become a realistic, robust, and non-invasive alternative to i.a. DSA in the diagnosis of paod.     

Continuously moving table MRI with SENSE: application in peripheral contrast enhanced MR angiography.

An integration of SENSitivity Encoding (SENSE) with continuously moving table (CMT) MRI for extended field-of-view (FOV) acquisitions is described. In this work, the approach in which receiver coils are attached to the object and move in synchrony with the scanner table is considered. Technical issues dealing with the implementation of SENSE-CMT are addressed, including coil calibration, correction for non-uniform magnetic gradients, and specific reconstruction steps. An explanation of combining SENSE with gradient non-linearity correction is given, as the latter becomes necessary in CMT acquisitions where a large sampling FOV is used. It is hypothesized that SENSE can provide at least a 2-fold improvement in lateral spatial resolution compared to non-accelerated CMT acquisitions. The hypothesis is tested in phantoms, where the effectiveness of both SENSE and gradient non-linearity correction to improve spatial resolution is shown. The SENSE-CMT technique is further demonstrated in vivo with contrast-enhanced MR angiography of the peripheral vasculature.     

Changes in visibility of intracranial arteries on MRA with normal ageing

We investigated age-related changes in the visibility of intracranial arteries on magnetic resonance angiography (MRA) and the influence of risk factors for stroke. We studied 230 adult patients without specific neurological deficits. MRA was performed using the three-dimensional time-of-flight technique with a spoiled gradient-recalled acquisition sequence. We classified internal carotid artery (IC) and the horizontal (M1) and distal (beyond M2) middle cerebral segments into 4 grades. Linear regression revealed a significant negative relation between age and the quality of demonstration on MRA. For IC and M1, the score was significantly lower in subjects with risk factors than in those without. The distal MCA was poorly seen in patients without a history of hypertension or lacunar infarcts. A marked correlation was observed between visibility and age patients with no history of hypertension, diabetes mellitus and hyperlipidaemia. We suggest that atherosclerotic change and decline in flow velocity with normal ageing are factors leading to decreased visibility on MRA. Received: 13 January 1998 Accepted: 6 January 1999     

腹主动脉、髂动脉及下肢动脉的MR数字减影血管造影

目的探讨增强ＭＲ血管造影的方法,评价快速梯度回波序列增强ＭＲ数字减影血管造影对腹主动脉、髂动脉及下肢动脉病变的诊断价值。方法３６例临床疑有腹主动脉、髂动脉或下肢动脉疾病的病人进行增强３Ｄ快速梯度回波扫描（重复时间１２或２０毫秒、回波时间４或５毫秒、反转角６０°）。对比剂用量０．２ｍｍｏｌ／ｋｇ。原始图像先进行减影处理,再进行最大信号强度投影（ＭＩＰ）重建。结果所有３６例患者（包括６例正常）均满意地显示了感兴趣区的血管。其中,腹主动脉夹层动脉瘤４例,肾动脉狭窄２例,人工血管移植术３例,腹主动脉瘤２例,髂动静脉瘘１例,髂动脉及下肢动脉狭窄１８例。结论三维磁共振数字减影血管造影是腹部及外周血管成像可靠的、充满活力的方法。     

Segmentation with gray-scale connectedness can separate arteries and veins in MRA

PURPOSE: To describe and present some preliminary results for a novel algorithm for segmentation with gray-scale connectedness as a means to separate arteries and veins in magnetic resonance angiography (MRA). MATERIALS AND METHODS: The proposed algorithm, SeparaSeed, uses the gray-scale degree of connectedness as a tool to find the zone surrounding each vessel, in order to split the original volume into its different vessel components. In contrast to traditional segmentation methods, no gray-scale information is lost in the process. The segmentation is performed in one step, resulting in a partition of the initial volume into a chosen number of regions of interest (ROIs). Finally, visualization is achieved by projecting the 3D vessel trees to 2D using the common maximum intensity projection (MIP). The algorithm was tested in two MRA data sets of the vessels of the pelvis acquired after injection of an intravascular contrast agent and in one data set of the vessels of the neck with gadolinium. RESULTS: In all data sets, a large proportion of the venous signal was removed while preserving that of the arteries, thus improving visualization of the relevant vessels. CONCLUSION: Separation of arteries and veins is feasible with the proposed algorithm with a moderate amount of interaction.     

3D time-resolved MR angiography (MRA) of the carotid arteries with time-resolved imaging with stochastic trajectories: comparison with 3D contrast-enhanced Bolus-Chase MRA and 3D time-of-flight MRA

BACKGROUND AND PURPOSE: Time-resolved MR angiography (MRA) offers the combined advantage of large anatomic coverage and hemodynamic flow information. We applied parallel imaging and time-resolved imaging with stochastic trajectories (TWIST), which uses a spiral trajectory to undersample k-space, to perform time-resolved MRA of the extracranial internal carotid arteries and compare it to time-of-flight (TOF) and high-resolution contrast-enhanced (HR) MRA.MATERIALS AND METHODS: A retrospective review of 31 patients who underwent carotid MRA at 1.5T using TOF, time-resolved and HR MRA was performed. Images were evaluated for the presence and degree of ICA stenosis, reader confidence, and number of pure arterial frames attained with the TWIST technique.RESULTS: With a consensus interpretation of all sequences as the reference standard, accuracy for identifying stenosis was 90.3% for TWIST MRA, compared with 96.0% and 88.7% for HR MRA and TOF MRA, respectively. HR MRA was significantly more accurate than the other techniques (P < .05). TWIST MRA yielded datasets with high in-plane spatial resolution and distinct arterial and venous phases. It provided dynamic information not otherwise available. Mean diagnostic confidence was satisfactory or greater for TWIST in all patients.CONCLUSION: The TWIST technique consistently obtained pure arterial phase images while providing dynamic information. It is rapid, uses a low dose of contrast, and may be useful in specific circumstances, such as in the acute stroke setting. However, it does not yet have spatial resolution comparable with standard contrast-enhanced MRA.

Stroke has an estimated prevalence of 5.7 million (2.6%) adults in the United States, where it is the third most common cause of mortality.¹ Atherosclerotic carotid artery disease is an important risk factor for anterior circulation ischemic stroke. Imaging evaluation is essential for optimal management and stroke prevention, as demonstrated in studies of symptomatic^2,3 and asymptomatic populations.^4,5 Carotid dissection is another potential cause of anterior circulation ischemia, which also requires high-spatial-resolution imaging for definitive diagnosis.Digital subtraction angiography (DSA) remains the gold standard for assessment of the cervical vasculature,⁶ with excellent spatial and temporal resolution. However, risks include vascular injury, intracerebral complications, contrast nephrotoxicity, and exposure to ionizing radiation. Therefore, noninvasive techniques are typically used initially. Duplex Doppler sonography, CT angiography (CTA), and MR angiography (MRA) all have high but varying degrees of sensitivity and specificity, ranging from 70% to 99% for carotid stenosis detection.⁷ Although sonography provides excellent dynamic information and spatial resolution, insonation window limitations restrict anatomic coverage. Similarly, long imaging times with time-of-flight (TOF) MRA also limit anatomic coverage. CTA and conventional arterial contrast-enhanced MRA offer extensive coverage but provide no dynamic information and are dependent on accurate timing for optimal visualization of the arterial tree.3D time-resolved contrast-enhanced MR angiography (TR MRA) has been previously described.⁸ TR MRA offers combined anatomic and hemodynamic information and obtains pure arterial and venous phase images consistently and rapidly without a timing run. More recently, the technique has been specifically applied to the extracranial carotid arteries using parallel imaging or keyhole imaging techniques.^9,10 In this study, we report the diagnostic accuracy of TR MRA of the extracranial internal carotid artery (ICA) acquired with a combination of parallel imaging (generalized autocalibrating partially parallel acquisition [GRAPPA])¹¹ and time-resolved imaging with stochastic trajectories (TWIST), a new view-sharing technique, which undersamples the periphery of k-space depending on the radial distance from the center of k-space.^12,13 We compared TR MRA with 3D high-resolution contrast enhanced MRA (HR MRA) and 3D TOF MRA.     

小腿3.0 T MRA:非增强心电门控流动依赖MRA、连续移床MRA和时间分辨MRA的对比研究

目的对一组临床病人行小腿3.0TMRA检查分析,旨在比较3D非增强心电门控流动依赖型MRA(NE-MRA)、连续移床(CTM)MRA和时间分辨TWIST-MRA的应用价值。方法 36例外周动脉硬化闭塞症(PAOD)病人(Ⅱ～Ⅳ     

Noncontrast‐enhanced peripheral MRA: Technical optimization of flow‐spoiled fresh blood imaging for screening peripheral arterial diseases

Flow‐spoiled fresh blood imaging, a noncontrast peripheral MR angiography technique, allows the depiction of the entire tree of peripheral arteries by utilizing the signal difference between systolic‐ and diastolic‐triggered data. The image quality of the technique relies on selecting the right triggering delay times and flow‐dependent read‐out spoiler gradient pulses. ECG triggering delays were verified using manual subtraction and automated software. The read‐out spoiler gradients pulses were optimized on volunteers before utilizing the flow‐spoiled fresh blood imaging technique to screen for peripheral arterial disease. Thirteen consecutive patients with suspected peripheral arterial disease underwent both flow‐spoiled fresh blood imaging and 16‐detector‐row computed tomography angiography examinations. A total of 23 segments were evaluated in the arterial vascular system. Using computed tomography angiography as the reference standard, 56 diseased segments were detected with 22 nonsignificant stenoses (<50%) and 34 significant stenoses, 15 of which were totally occluded. Flow‐spoiled fresh blood imaging had a sensitivity of 97%, a specificity of 96%, an accuracy of 96%, a positive predictive value of 88%, and a negative predictive value of 99%. With such a high negative predictive value, flow‐spoiled fresh blood imaging has the potential to become the safest noninvasive screening tool for peripheral arterial disease, especially for patients with impaired renal function. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Quantitative and qualitative evaluation of the influence of different table feeds on visualization of peripheral arteries in CT angiography of aortoiliac and lower extremity arteries

The influence of different table feeds (TF) on vascular enhancement and image quality in patients undergoing lower extremity runoff-CTA for peripheral artery occlusive disease (PAOD), acute ischemia (AI) or abdominal aortic aneurysm (AAA) with PAOD was investigated retrospectively. One hundred eighty-five patients (PAOD: n = 132; AI: n = 40; AAA: n = 13) underwent 16-detector runoff-CTA (120 kV; 140 mAs; rotation time 0.5 s, collimation 16 x 1.5 mm) using different TF (30 mm/s: n = 25; 40 mm/s: n = 91; 48 mm/s: n = 36; 56 mm/s: n = 33). Vascular enhancement of the large arteries was measured every 10 cm along the z-axis from the upper abdomen to the toe. Arterial enhancement in the distal lower leg was compared (ANOVA, Bonferroni post-test). Qualitative assessment of bolus timing was performed independently by two radiologists. The study was IRB approved. In patients with PAOD or AI, enhancement of calf arteries using a TF of 48 mm/s (278 +/- 79 HU) was significantly higher in comparison to two slower TF (30 mm/s: 201 +/- 70 HU, P < 0.001; 40 mm/s: 251 +/- 79 HU, P < 0.05; 56 mm/s: 261 +/- 57 HU, NS) and the fewest noninterpretable arterial segments below the knee were observed with a TF of 48 mm/s (reader 1: 5/121 = 4.1%; reader 2: 4/121 = 3.3%). In patients with AAA, the fewest nondiagnostic segments occurred with a TF of 30 mm/s (2/12 = 17%, both readers) and 40 mm/s (4/24 = 17%, both readers). A TF of 48 mm/s provided the best synchronization of CT data acquisition and contrast bolus propagation and thus the best image quality in patients with PAOD and AI. In patients with AAA, a slower TF of 30 mm/s provided better image quality than faster CT protocols.