《心血管核磁技术临床进展》由会员分享，可在线阅读，更多相关《心血管核磁技术临床进展（16页珍藏版）》请在金锄头文库上搜索。
1、CLINICAL APPROACH TO CMR TECHNIQUES 13COILS Standard body coil Standard surface coil Dedicated cardiac phased array coil constructed of multiple elements (the best alternative)further improved image qualityspatial resolutionLarger field of viewPhased array coils allow application of SENSE technique.
2、SENSE TECHNIQUE It represents a revolutionizing technology in CVMR; The principle is based on parallel imaging with use of all coil elements; Each coil has a different sensitivity profile, which can be exploited to unfold undersampled acquisitons and to reduce the density of the acquired k-space dat
3、a, thus speeding up scan time; Using SENSE, currently, a twofold increasing imaging speed can be obtained as standard; Setting higher factors were reachedCARDIAC MOTION COMPENSATION Is performed by synchronizing the image acquisition to the electrocardiogram (ECG) signals. Imaging formation in MR is
4、 based on filling k-space during data acquisition. ECG-triggering is aimed at filling k-space in multiple steps, based on the timing within the cardiac cycle. Two type of ECG triggering method Prospective triggering(image acquisition starts at a fixed delay after the QRS-complex of the ECG and stops
5、 around 80% of the cardiac cycle, the last 20% of cycle is not imaged, this technique is suitable to image systolic heart function) Retrospective ECG gating (when need to evaluate diastolic hear function. Its acquires image data irrespective of the ECG, while the ECG is recorded in parallel. Once th
6、e MR acquisition is finished, the computer calculates afterward (retrospectively)the appropriate cardiac phases, based on the stored ECG and k-space data.) (is now the standard for most CVMR imaging purpose) A major problem for clinical application of cardiac CVMR is the practical worry of obtaining
7、 a reliable ECG signal from a patient inside the MR scanner. Recently, a new approach was launched to correct this problem-the vector ECG (VCG), it based on the 3-dimensional orientation of the QRS-complex and T wave of the ECG and the distorting component, the MR acquisition can be triggered by QRS
8、-complex only and not by mistake by the T- wave or ECG distortions or the signal induced by gradient switching.RESPIRATORY MOTION COMPENSATION Past days: ROPE and PEAR techniques used. Due to development of faster MR imaging techniques, such as echo-planar imaging and trubo-field echo imaging, it be
9、came possible to acquire image data during a short breath-hold of around 15 seconds. Optimal quality can be obtained by using the respiratory navigator technique only. Usually, the navigator beam is positioned on the right hemi-diaphragm and is acquired before and after every MR data acquisition blo
10、ck, with an acquisition duration of only 30 milliseconds. Real-time prospective respiratory navigator. A window around the end-expiration position of the diaphragm is defined, determining the positions in which MR data is accepted. Respiratory navigators can also be used for slice tracking, which me
11、ans that the slice position is adjusted respective to the breathing changes detected by the navigator. The combination of these tow techniques seems, currently, the best solution. Recent techniques are combinations of turbo-field echo, echo-planar, or spiral k-space acquisition. The image spatial re
12、solution is still quite low, allowing only evaluation of ventricular volume changes and some rough estimation of wall motion abnormalities. In the future: Combination of the ultrafast acquisition schemes with SENSE may allow higher resolution imaging. A promising technique for ultrafast whole heart
13、functional imaging in a single breath-hold is the so-called k-t BLAST technique. Another promising development is real-time imaging of the heart. (recently, data has been presented showing full ventricular coverage in real-time without the need for ECG-triggering or breath-holding)SCOUT/SURVEY A dec
14、ade ago, Multi-slice spin-echo technique, sometimes in combination with turbo spin-echo used. A faster technique for acquiring survey images is, for example, a turbo- field-echo or turbo-field-echo-planar MR sequence. Recently, balanced gradient echo (bFFE, bTFE, true-FISP) techniques became availab
15、le, yielding images with high contrast between bold and myocardium. Currently, excellent images can be obtained using balanced-FFE without respiratory motion compensation, with an acquisition time of only 15 seconds.PLANSCAN Real-time planning toolAllowing routine application of cardiovascular MR Us
16、e the survey images as input for an algorithm, which plans automatically the desired imaging planes.Currently available only off-line as a research tool.THE STEPPING STONE IN CARDIOVASCULAR MR Anatomy Function Perfusion Delayed enhancement Flow Coronary MR angiography Vessel wall imagingFUNCTION Evaluation of myocardial wall motion abnormalities in patients with suspected myocardial ischemia.
