1. Introduction
Strokes are the leading cause of adult disability in the world and are the number two cause of death worldwide [1]. A stroke can be cast into two major categories, ischemic and haemorrhagic [2]. A haemorrhagic stroke occurs when a blood vessel bursts inside the brain; the blood accumulates and compresses the surrounding brain tissue. The course of treatment for ischemic and haemorrhagic strokes is different [3]. An initial examination done by a physician is typically clinical using a neurological exam. This however is not always conclusive as many non-vascular conditions can simulate stroke symptoms [4]. As such, physicians primarily rely on medical imaging systems such as the computed tomography (CT) scan and magnetic resonance imaging (MRI) for confirmation of the diagnosis. The complexity of stroke diagnosis emphasizes the vital importance played by the CT and MRI scan systems. They are however, not fast, cost effective or portable, nor are they accessible at rural medical clinics, or carried by first response paramedical teams. Microwave imaging for detecting brain abnormalities has recently been proposed [5]–[7]. Diagnostic microwave imaging exploits the differences in tissues' dielectric properties. It has been demonstrated that brain stroke changes the dielectric properties of the tissues. Haemorrhagic stroke leads to a significant increase in the dielectric properties (up to 20%) with respect to the dielectric properties of the white/grey matter [2]. Potentially, microwave imaging can supplement current diagnostic methods as it may potentially provide a fast, cost effective and portable detection system [6]. Specifically, in recent years, there has been a growing interest in the development of imaging methods such as those using the microwave imaging technique for medical applications. Its use of non-ionizing signal, low cost, low complexity and its ability to penetrate through mediums are the benefits of microwave technology which has recently attracted the attention of researchers [8]. Current research in microwave imaging can be divided mainly into tomography and linear scattering techniques. Among linear scattering techniques, the HP based technique allows to detect dielectrics inhomogeneities in frequency domain [6]. In addition, HP requires a very simple hardware set-up, i.e., one transmitting antenna and one receiving antenna (coupled through a Vector Network Analyser) which rotate around the object to collect the signals in a multi-bistatic fashion. Up to now, HP has been used for breast cancer and skin cancer detection. The aim of this paper is to provide initial results on the efficacy of HP microwave imaging for haemorrhagic stroke detection. This is done using both simulations and measurements in an anechoic chamber. This paper is organized as follows: Section 2 explains the antenna design and simulation. In Section 3, the measurements are demonstrated. Results are discussed in Section 4, and finally Section 5 concludes the paper.