Contrast-enhanced time-resolved 4D MRA of congenital heart and vessel anomalies: image quality and diagnostic value compared with 3D MRA

Objectives

To evaluate time-resolved interleaved stochastic trajectories (TWIST) contrast-enhanced 4D magnetic resonance angiography (MRA) and compare it with 3D FLASH MRA in patients with congenital heart and vessel anomalies.

Methods

Twenty-six patients with congenital heart and vessel anomalies underwent contrast-enhanced MRA with both 3D FLASH and 4D TWIST MRA. Images were subjectively evaluated regarding total image quality, artefacts, diagnostic value and added diagnostic value of 4D dynamic imaging. Quantitative comparison included signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel sharpness measurements.

Results

Three-dimensional FLASH MRA was judged to be significantly better in terms of image quality (4.0?±?0.6 vs 3.4?±?0.6, P?<?0.05) and artefacts (3.8?±?0.4 vs 3.3?±?0.5, P?<?0.05); no difference in diagnostic value was found (4.2?±?0.4 vs 4.0?±?0.4); important additional functional information was found in 21/26 patients. SNR and CNR were higher in the pulmonary trunk in 4D TWIST, but slightly higher in the systemic arteries in 3D FLASH. No difference in vessel sharpness delineation was found.

Conclusions

Although image quality was inferior compared with 3D FLASH MRA, 4D TWIST MRA yields robust images and added diagnostic value through dynamic acquisition was found. Thus, 4D TWIST MRA is an attractive alternative to 3D FLASH MRA.

Key Points

? New magnetic resonance angiography (MRA) techniques are increasingly introduced for congenital cardiovascular problems. ? Time-resolved angiography with interleaved stochastic trajectories (TWIST) is an example. ? Four-dimensional TWIST MRA provided inferior image quality compared to 3D FLASH MRA but without significant difference in vessel sharpness. ? Four-dimensional TWIST MRA gave added diagnostic value.     

New developments in MRA: time-resolved MRA

For many clinical questions, less invasive angiography methods have at least in part already replaced digital subtraction angiography (DSA) as a routine diagnostic procedure. However, temporal resolution achievable with DSA is still indispensable in some patients. Recent advances in MR hardware performance and imaging techniques permit sub-second frame rate MR angiographies to be performed using a rapidly repeated fast T1 weighted gradient echo sequence during administration of a contrast bolus, and subsequent complex subtraction in k-space to emphasise the difference in phase between stationary tissue and contrast-enhanced blood. This technique allows two-dimensional projection angiograms to be obtained at a temporal frame rate of three images per second and with a spatial in-plane resolution of about one square millimetre. This time-resolved information is important for (a) the detection and follow-up of arteriovenous malformations, including their arterial feeders, the size of the nidus and their venous drainage patterns, (b) the demonstration of dural arteriovenous fistulas, recognised as an early filling of a dural sinus during the early arterial phase, and (c) the characterization of the vascularisation of brain tumours. With regards to vascular malformations, the direction of venous drainage and therefore the most pressing clinical questions concerning the need for therapeutic intervention can be ascertained. This technique is the only MR imaging method able to provide dynamic information on the cerebral vasculature. It therefore constitutes a helpful adjunct to the imaging armentarium in many clinical situations.     

Contrast-enhanced 3D MRA using SENSE

Sensitivity encoding (SENSE) was used to improve the performance of three-dimensional contrast-enhanced magnetic resonance angiography (3D CE-MRA). Utilizing an array of receiver coils for sensitivity encoding, the encoding efficiency of gradient-echo imaging was increased by factors of up to three. The feasibility of the approach was demonstrated for imaging of the abdominal vasculature. On the one hand, using a SENSE reduction factor of two, the spatial resolution of a breath-hold scan of 17 seconds was improved to 1.0 x 2.0 x 2.0 mm(3). On the other hand, using threefold reduction, time-resolved 3D CE-MRA was performed with a true temporal resolution of 4 seconds, at a spatial resolution of 1.6 x 2.1 x 4.0 mm(3). CE-MRA with SENSE was performed in healthy volunteers and patients and compared with a standard protocol. Throughout, diagnostic quality images were obtained, showing the ability of sensitivity encoding to enhance spatial and/or temporal resolution considerably in clinical angiographic examinations.     

Computer-based imaging and interventional MRI: applications for neurosurgery.

Advances in computer technology and the development of open MRI systems definitely enhanced intraoperative image-guidance in neurosurgery. Based upon the integration of previously acquired and processed 3D information and the corresponding anatomy of the patient, this requires computerized image-processing methods (segmentation, registration, and display) and fast image integration techniques. Open MR systems equipped with instrument tracking systems, provide an interactive environment in which biopsies and minimally invasive interventions or open surgeries can be performed. Enhanced by the integration of multimodal imaging these techniques significantly improve the available treatment options and can change the prognosis for patients with surgically treatable diseases.     

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.     

Contrast-enhanced peripheral MRA: technique and contrast agents

In the last decade contrast-enhanced magnetic resonance angiography (CE-MRA) has gained wide acceptance as a valuable tool in the diagnostic work-up of patients with peripheral arterial disease. This review presents current concepts in peripheral CE-MRA with emphasis on MRI technique and contrast agents. Peripheral CE-MRA is defined as an MR angiogram of the arteries from the aortic bifurcation to the feet. Advantages of CE-MRA include minimal invasiveness and lack of ionizing radiation. The basic technique employed for peripheral CE-MRA is the bolus-chase method. With this method a paramagnetic MRI contrast agent is injected intravenously and T1-weighted images are acquired in the subsequent arterial first-pass phase. In order to achieve high quality MR angiograms without interfering venous contamination or artifacts, a number of factors need to be taken into account. This includes magnetic field strength of the MRI system, receiver coil configuration, use of parallel imaging, contrast bolus timing technique, and k-space filling strategies. Furthermore, it is possible to optimize peripheral CE-MRA using venous compression techniques, hybrid scan protocols, time-resolved imaging, and steady-state MRA. Gadolinium(Gd)-based contrast agents are used for CE-MRA of the peripheral arteries. Extracellular Gd agents have a pharmacokinetic profile similar to iodinated contrast media. Accordingly, these agents are employed for first-pass MRA. Blood-pool Gd-based agents are characterized by prolonged intravascular stay, due to macromolecular structure or protein binding. These agents can be used for first-pass, as well as steady-state MRA. Some Gd-based contrast agents with low thermodynamic stability have been linked to development of nephrogenic systemic fibrosis in patients with severe renal insufficiency. Using optimized technique and a stable MRI contrast agent, peripheral CE-MRA is a safe procedure with diagnostic accuracy close to that of conventional catheter X-ray angiography.     

Experimental models in interventional neuroradiology.

Various experimental models have been developed to test interventional neuroradiologic techniques. Most have been used to test various devices and embolic materials, and a small number of models have been designed for teaching or training purposes. Experimental models in endovascular techniques have seldom been used to stimulate disease processes in order to facilitate their understanding.     

Magnetization transfer: applications in neuroradiology

Magnetization transfer imaging is a technique that was introduced into clinical radiology in the early nineteen nineties and which has gained in popularity ever since, particularly in the field of neuroradiology. This paper presents an overview of the clinical and scientific applications of magnetization transfer imaging in neuroradiology.     

Standards of practice in interventional neuroradiology

The growing importance of INR has resulted in the need to define and promote professional standards of clinical practice. Several professional organizations have published guidelines recently for the neurointerventional treatment of cerebrovascular diseases, including technical and personal recommendations, but detailed definitions of technical and organizational conditions needed for the safe and effective performance of such treatments are lacking. To fill this gap ESNR, ESMINT and the UEMS Division for Neuroradiology established a working group, to develop a consensus paper on “Standards of Practice in Interventional Neuroradiology”. This document is the result of the Consensus Working Group and has following review gained approval by the Executive Boards of ESNR and ESMINT and by the members of the UEMS Division for Neuroradiology in 2017.

     

动态增强磁共振血管成像技术及应用优势

目的 探讨动态增强磁共振血管成像(DCE MRA)技术要点及临床应用优势。资料与方法 对35例疑有血管性病变的患者，行DCEMRA扫描，最大信号强度投影(MIP)重建。结果35例均获得了清晰的血管图像，其中8例正常，27例异常。结论 DCE MRA为新的MRA技术，克服了常规MRA及对比增强MRA的缺点，成像效果与DSA相仿，因此具有极大的临床应用价值。     

Isolated oculomotor nerve palsy in interventional neuroradiology

Background

Isolated oculomotor nerve palsy (IOP) can be annoying for a patient and can also be the only clue to a potentially devastating and life-threatening disease. In order to understand its clinical spectrum and management better we analyzed the files of 13 patients seen at our institution over a 3-year period.

Methods

Thirteen consecutive patients with IOP between January 2005 and August 2008 presented to our hospital. Magnetic resonance imaging and angiography were employed as investigations tailored to the individual patient. A vascular disorder [i.e. arteriovenous fistula, aneurysm of the posterior communicating artery (Pcoma)] was found in 7 patients (63%), most commonly a dural carotid-cavernous sinus fistula (DCCF) or a Pcoma aneurysm.

Results

In 7 patients with a vascular abnormality (4 DCCFs; 3 Pcoma aneurysms), IOP was the presenting symptom. Pcoma aneurysms were coiled endovascularly and DCCFs were managed transvenously. Of the patients with more than 1 year (6 months to 2 years) of follow-up, all 7 endovascular patients recovered completely. Time to complete resolution of ONP was 6 months.

Conclusion

Patients with IOP should be investigated with noninvasive techniques (MRI and MRA). If these are negative or to clarify abnormal findings of noninvasive techniques, selective angiography is needed for diagnosis and to guide treatment.     

Rui Liao's work on patient-specific 3-D model guidance for interventional and hybrid-operating-room applications

Compared to surgery,interventional and hybrid-operating-room(OR) approaches diagnose or treat pathology with the most minimally invasive techniques possible.By minimizing the physical trauma to the patient,peripheral or hybrid approaches can reduce infection rates and recovery time as well as shorten hospital stays.Minimally invasive approaches therefore are the trend and often the preferred choice,and may even be the only option for the patients associated with high surgery risks.Common interventional imaging modalities include 2-D X-ray fluoroscopy and ultrasound.However,fluoroscopic images do not display the anatomic structures without a contrast agent,which on the other hand,needs to be minimized for patients’ safety.Ultrasound images suffer from relatively low image quality and tissue contrast problems.To augment the doctor’s view of the patient’s anatomy and help doctors navigate the devices to the targeted area with more confidence and a higher accuracy,high-resolution pre-operative volumetric data such as computed tomography and/or magnetic resonance can be fused with intra-operative 2-D images during interventions.A seamless workflow and accurate 2-D/3-D registrationas well as cardiac and/or respiratory motion compensation are the key components for a successful image guidance system using a patient-specific 3-D model.Dr.Liao’s research has been focused on developing methods and systems of 3-D model guidance for various interventions and hybrid-OR applications.Dr.Liao’ s work has led to several Siemens products with high clinical and/or market impact and a good number of scientific publications in leading journals/conferences on medical imaging.     

Fabrication of microballoons for interventional neuroradiology: preliminary report

A simple and inexpensive method of making latex microballoons for neuroradiologic procedures is described. The balloons have been tested in experimental animals and used in human clinical procedures. Preliminary experience and results are presented.     

Combined time-resolved and high-spatial-resolution 3D MRA using an extended adaptive acquisition

PURPOSE: To combine the benefits of time-resolved dynamic imaging and single elliptical centric acquisitions in a reasonable scan time. MATERIALS AND METHODS: A time series of images with moderate spatial resolution was acquired using the 3D Time-Resolved Imaging of Contrast KineticS (3D TRICKS) technique with elliptical centric encoding during contrast arrival. Following venous opacification, a complete large centrically encoded k-space volume was acquired. The high-spatial-frequency portions of this volume were combined with a 3D TRICKS time frame to form a high-resolution image. An additional single image is formed by suppressing background and signal averaging all acquired data, including post-venous low-spatial-frequency data. For this image, 2D temporal correlation analysis is used to suppress low-spatial-frequency vein contributions. Arrival time and spatial correlations are used to suppress background. RESULTS: The 3D TRICKS time frame may be selected to ensure a combined high-resolution image that has optimal central k-space sampling for any vascular region. The single image formed by signal averaging all acquired data has increased contrast-to-noise (CNR) and signal-to-noise (SNR) ratios. CONCLUSION: The advantages of time-resolved and high-spatial-resolution imaging were combined using an extended dual-phase acquisition. Some SNR and CNR gain was achieved by signal averaging. This process is facilitated by background and vein suppression.     

Contrast-enhanced 3D-TOF MRA of peripheral vessels: Intravascular versus extracellular MR contrast media

MR contrast media have been used to improve MR angiography (MRA). Their effect has been particularly beneficial for extracranial MRA. This study evaluated the efficacy of a new formulation of ultrasmall super-paramagnetic iron oxide particles (USPIO) on three-dimensional (3D) time of flight (TOF) MRA in the pelvis and lower limb circulation. Each of six dogs received 3 mg/kg of USPIO and .2 mmol/kg of gadolinium-dieth-ylenetriamine pentaacetic acid (Gd-DTPA) bis-meth-ylamide (BMA) by intravenous infusion on separate examinations. Precontrast and postcontrast 3D-TOF MRA images of the lower extremities were acquired over the course of 45 minutes postinjection. Signal intensity (SI) was measured on axial views along the external iliac, femoral, and popliteal arteries. USPIO provided clear demarcation of the major primary, secondary, and tertiary vessels and the improved contrast-to-noise ratio (CNR) was maintained for 45 minutes. Gd-DTPA-BMA provided less signal enhancement than USPIO. The increase in CNR with this agent had significantly declined by 15 minutes after injection. The major vessels could no longer be visualized at 30 and 45 minutes after injection of Gd-DTPA-BMA. This study demonstrates the efficacy of USPIO as a contrast medium for 3D-TOF MRA. It was concluded that USPIO provided effective and persistent enhancement of the peripheral vessels.