In this paper, we proposed an improved scan method of MRA, which displays lateral thoracic artery, thoracodorsal artery, and lymph nodes clearly and completely. Based on conventional DCE-THRIVE, the e-THRIVE sequence was added in coronal direction instead of transverse. After the original scanning data were obtained, we reconstructed them by MIP, MPR, VR to reflect the course of arteries and the situation of lymph nodes from various perspectives. Through reasonable statistical analysis, we had proved that the image quality of the coronal e-THRIVE sequence is superior to that of the conventional DCE-THRIVE scan, especially on displaying arteries and lymph nodes. The coronal e-THRIVE scan is feasible and has a clinical reference value. Meanwhile, these scanning had lower requirements for equipment, while the results improved significantly. It reduces the cost of imaging examination for patients and makes it easier to popularize MRA in breast screening.
Image diagnosis is one of the common methods for direct and rapid diagnosis of disease [14]. In MRA studies, the cardiovascular [15], lower extremities [16], cerebrovascular [17], carotid artery [18], etc. are the major research work. However, there are few studies on breast angiography, and the imaging of breast vessels and their branches is of great help to the diagnosis of breast diseases [19]. Vessels can also be used for surgical treatment [20]. Petrillo A. et al. [21] used contrast-enhanced MRI and a semi-automatic procedure to obtain a breast vascular map and evaluated the correlation between vessels and tumor location. Vasile et al. [22] located the position of vessels by using MRA. The position is useful for the surgery of perforator flap breast reconstruction. The imaging methods used in these studies are all transverse imaging. However, there is a problem in practice that the z-axis scan range is limited, resulting in the loss of detailed information. We conducted a coronary imaging study that showed a significant improvement in the completeness of breast artery information capture compared to conventional methods.
The conventional methods are usually transverse scanning and dynamic sequence is used to obtain the original data after plain scanning. In order to obtain better temporal resolution, the dynamic enhancement sequence should be coordinated with breast wash in and out. During the scanning process, one phase image is generated every minute. The problems of the method are as follows: the thickness of the layer is too large, which brings difficulties to the later 3D reconstruction; the coverage area in the direction from head to feet is small, usually around 170 mm, which cannot cover the beginning of arteries and the ending of branches. If the coverage area expands by increasing the number of layers, the scanning time will be too long. It brings pain to patients. If the coverage area expands by increasing the layer thickness, the resolution of the z-axis will reduce again. Whether the thickness is too large or the coverage area is too small, the information of the breast area will lose, resulting in a false-negative diagnosis, which harms the health of the patients. By adding the coronal e-THRIVE scan mentioned in this paper, the spatial resolution is improved to 0.9 × 0.9 × 0.9 mm, covering a range of about 240 mm on the z-axis of the human body with an appropriate signal-to-noise ratio. We chose an arterial phase to reconstruct Fig. 6a in the process of DCE-THRIVE. Then, in the process of coronal e-THRIVE of the same patient, we reconstruct Fig. 6b of the same area. It can be seen that coronal e-THRIVE is better in the reconstruction of coronal plane images for arteries and lymph nodes display.
In clinical practice, 16 channels MR scanning machines, which have large magnetic fields are common. These types of equipment can get high-quality images. While the proposed improved method can obtain equal image quality by 1.5 T machine with 8 channels, which is of great significance to reduce the cost of examination and promote the popularization of MRA examination. In addition, the coronal e-THRIVE sequence was added after the routine DCE-THRIVE to combine routine breast examination with angiography. Patients were injected with contrast agent only one time. They can get high-quality images of breast arteries and lymph nodes while completing the routine examination. On the one hand, it will not increase the economic burden of patients; the dosage of contrast agents will not increase, which ensures the safety of patients and reduces the pain and health burden of patients. For hospitals and doctors, it also improves work efficiency.
Limitations
In addition, this method also has some shortcomings. The main problem is that the scanning time will increase about 2 min compared with DCE-THRIVE because of adding the coronal e-THRIVE sequence. The extension of time may cause pain for some patients. The process of image reconstruction may be influenced by noise from outside or caused by the reconstruction method itself, which leads to image blurring or inaccurate [23]. For accurate measurements, these effects should be removed by preprocessing [24,25,26], which should be considered in the future of work. And the other problem is that the research results in this paper are mainly limited to the acquisition of morphology of lateral thoracic artery, thoracodorsal artery, and lymph nodes, and there is a lack of quantitative analysis in terms of location and quantity, which need more clinical practice not just imaging analysis. Besides, some other factors may affect the image quality, such as (1) the movement of patients caused by too long time and uncomfortable position; (2) motion artifact caused by heartbeat and breathing; (3) the main magnetic field is uneven caused by poor equipment state, and leading to the poor effect of fat suppression which affects the display of arteries; (4) the problems of blood circulation of patients; (5) the dosage of contrast agent is not suitable. In summary, the technique of breast MRA still has some room for improvement.
