Microwave Detection For Large Vessel Occlusion
Doctoral thesis, 2025
Stroke is the second leading cause of death worldwide, placing a substantial burden on patients and healthcare systems. Early treatment is crucial for patient outcomes, particularly in the case of large-vessel occlusions, where thrombectomy is indicated but only performed in a limited number of hospitals. Consequently, rapid and accurate prehospital detection is essential to expedite proper treatment.
This work proposes a microwave-based diagnostic approach enhanced by saline as a contrast enhancement agent to identify large-vessel occlusions. By exploiting the asymmetry in cerebral blood flow caused by partial or complete arterial blockage, the system detects conductivity variations via microwaves transmitted and received by antennas placed on the head. Three antennas are used, and a new dielectric rod antenna design is introduced to reduce multipath interference through surface waves. Compared to a self-grounded bow-tie antenna, the dielectric rod antenna decreases surface wave power by up to 10 dB and expands bandwidth by 72%.
An exploratory animal study was conducted to establish realistic measurement protocols for replicating large-vessel occlusions. Two signal processing algorithms were developed: one detects deviations based on signal power changes, and the other interprets these changes in the context of conductivity enhancement and pathophysiology. Data analysis demonstrated statistically significant changes in measured asymmetry due to saline injection, aligning with expected physiological responses.
These findings suggest that microwave-based prehospital detection of large vessel occlusions is feasible. The proposed method holds promise for improving stroke triage by enabling faster, more reliable identification of thrombectomy candidates, ultimately reducing treatment delays and improving patient outcomes.
This work proposes a microwave-based diagnostic approach enhanced by saline as a contrast enhancement agent to identify large-vessel occlusions. By exploiting the asymmetry in cerebral blood flow caused by partial or complete arterial blockage, the system detects conductivity variations via microwaves transmitted and received by antennas placed on the head. Three antennas are used, and a new dielectric rod antenna design is introduced to reduce multipath interference through surface waves. Compared to a self-grounded bow-tie antenna, the dielectric rod antenna decreases surface wave power by up to 10 dB and expands bandwidth by 72%.
An exploratory animal study was conducted to establish realistic measurement protocols for replicating large-vessel occlusions. Two signal processing algorithms were developed: one detects deviations based on signal power changes, and the other interprets these changes in the context of conductivity enhancement and pathophysiology. Data analysis demonstrated statistically significant changes in measured asymmetry due to saline injection, aligning with expected physiological responses.
These findings suggest that microwave-based prehospital detection of large vessel occlusions is feasible. The proposed method holds promise for improving stroke triage by enabling faster, more reliable identification of thrombectomy candidates, ultimately reducing treatment delays and improving patient outcomes.
An- tenna
Biomedical Signal Procsseing
Large Vessel Occlusion
Microwave
Stroke
Brain Edema.
Thrombectomy
EE, Hörsalsvägen 11, Chalmers
Opponent: Prof. Francesca Vipiana, Politecnico di Torino
Author
Seyed Moein Pishnamaz
Chalmers, Electrical Engineering, Signal Processing and Biomedical Engineering
Seyed Moein Pishnamaz, Xuezhi Zeng, Hana Dobšíček Trefná, Mikael Persson, Andreas Fhager, “Microwave-Based Detection of Large Vessel Occlusion Using Contrast Enhancement
Seyed Moein Pishnamaz, Xuezhi Zeng, Hana Dobšíček Trefná, Mikael Persson, Andreas Fhager, “Microwave-Based Detection of Large Vessel Occlusion Using Contrast Enhancement- A Frequency-Derivative Analysis
Seyed Moein Pishnamaz, Xuezhi Zeng, Hana Dobšíček Trefná, Mikael Elam, Andreas Fhager, Mikael Persson, “Investigating the Effects of Saline Injection as a Contrast Enhancement Agent in Microwave Diagnostics of Large Vessel Occlusion
112 Dispatcher: What is your emergency?
Caller: I think someone is having a stroke! Their face is drooping on one side, and they can’t smile properly. Their left arm is really weak, and they can’t lift it up.
112 Dispatcher: Stay calm! Help is on the way.
20 minutes later in the ambulance...
Paramedic 1: We have confirmed stroke symptoms. What is your guess? Is it a large or small infarction? or even a bleeding?
Paramedic 2: Alright. We need a hospital with a stroke center for this case. The closest is Hospital A, but it doesn’t have a thrombectomy-capable unit that can handle large clots. Hospital B is 1 hour further away, and they have one. Which hospital should we go to?
Paramedic 1: If it is a large vessel occlusion, Hospital A won’t be able to remove the clot, and transferring later to Hospital B could cost valuable time!
Paramedic 2: But if it’s not a large vessel occlusion, we’d be bypassing a closer hospital where they could already be getting a clot-resolving medication. It’s a tough call!
The purpose of this research is to help make a better-informed decision in such scenarios. The focus is on developing a fast and portable method based on microwaves that can help detect large vessel occlusions before patients reach the hospital. The method is tested on sheep where the blood flow to one side of the brain is blocked. An injection of salt solution into a blood vessel creates a detectable asymmetry that can be measured by microwaves and used in a detection algorithm.
The research contains several different parts, from antenna system design to analyses of microwave measurements. Several physiological processes in the brain that potentially can interfere with the measurements were studied and modeled, for example, swelling of the brain due to a stroke-induced water buildup (edema).
Overall, this research indicates that early detection of large vessel occlusion is feasible and opens the door for future clinical trials. With the help of microwaves, paramedics will no longer need to guess which hospital to transport the patient to.
Caller: I think someone is having a stroke! Their face is drooping on one side, and they can’t smile properly. Their left arm is really weak, and they can’t lift it up.
112 Dispatcher: Stay calm! Help is on the way.
20 minutes later in the ambulance...
Paramedic 1: We have confirmed stroke symptoms. What is your guess? Is it a large or small infarction? or even a bleeding?
Paramedic 2: Alright. We need a hospital with a stroke center for this case. The closest is Hospital A, but it doesn’t have a thrombectomy-capable unit that can handle large clots. Hospital B is 1 hour further away, and they have one. Which hospital should we go to?
Paramedic 1: If it is a large vessel occlusion, Hospital A won’t be able to remove the clot, and transferring later to Hospital B could cost valuable time!
Paramedic 2: But if it’s not a large vessel occlusion, we’d be bypassing a closer hospital where they could already be getting a clot-resolving medication. It’s a tough call!
The purpose of this research is to help make a better-informed decision in such scenarios. The focus is on developing a fast and portable method based on microwaves that can help detect large vessel occlusions before patients reach the hospital. The method is tested on sheep where the blood flow to one side of the brain is blocked. An injection of salt solution into a blood vessel creates a detectable asymmetry that can be measured by microwaves and used in a detection algorithm.
The research contains several different parts, from antenna system design to analyses of microwave measurements. Several physiological processes in the brain that potentially can interfere with the measurements were studied and modeled, for example, swelling of the brain due to a stroke-induced water buildup (edema).
Overall, this research indicates that early detection of large vessel occlusion is feasible and opens the door for future clinical trials. With the help of microwaves, paramedics will no longer need to guess which hospital to transport the patient to.
Diagnostics for stroke and brain trauma in ambulances
Swedish Research Council (VR) (2021-03756), 2022-01-01 -- 2025-12-31.
Areas of Advance
Health Engineering
Subject Categories (SSIF 2025)
Neurology
Medical Biotechnology
Electrical Engineering, Electronic Engineering, Information Engineering
ISBN
978-91-8103-164-5
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5622
Publisher
Chalmers