Improving millimeter-wave imaging quality using the vortex phase method

This paper investigates a new vortex wave imaging approach to improve the imaging quality of small metal targets of size less than 1.5 mm.Antennas with different spiral phase plates are designed to efficiently transmit vortex beams with orbital angular momentums(OAMs).By analyzing the OAM spectrum of the target,it was discovered that the predominant reflection contains a particular OAM mode that carries abundant azimuthal information.This can be explained by the OAM selectivity of the target and the guidance of the vortex transmitting beam.A simple reflection vortex imaging system was designed to capture the phase information.Measurement results show that the high image contrast reaches 14.9%,which is twice as high as that of the imaging without OAM.Both of simulations and experiments demonstrate that the vortex phase imaging approach proposed in this paper can effectively improve the imaging quality at 80 GHz.This approach is suitable for other millimeter wave imaging systems and is helpful to improve the resolution in anti-terrorism security checks.

肝脏局灶性结节增生:MRI表现及其病理特征

目的探讨肝脏局灶性结节增生（focalnodular hyperplasia，FNH）确诊和误诊病例的MRI征象及其病理特征，提高对FNH的诊断和鉴别诊断的准确性。方法回顾性分析经手术病理证实的49例FNH患者（62个病灶）的MRI影像资料，总结FNH的MRI表现特点；回顾性分析12例MRI误诊为FNH（或诊断不够准确）的病例，总结FNH与其他病变MRI的鉴别诊断要点。结果FNH多分布在肝脏包膜下或部分突m于肝脏轮廓外（57／62），〉3cm的可以有分叶或浅分叶状（48／50），多数无包膜（57／62），少数可有假包膜样强化（5／62）；FNH因病灶大小不同，瘢痕显示率及其强化特征有所差异：瘢痕显示率在〉3cm的病灶中比较高（43／50），中央瘢痕强化在3～7cm的病灶中相对较高（15／39），瘢痕收缩征在〉7cm的病灶中相对较高（8／11）；大部分需要鉴别的病例，仔细阅片可以发现误诊或诊断不够准确的原因。结论充分认识瘢痕显示及其强化特征因病灶大小不同而产生的差异可以提高FNH诊断的准确性；注意影像细节并结合临床资料，可以提高对不典型FNH与其他病变的鉴别诊断的准确性。