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Image-Guided Radiation Therapy (IGRT) and Motion Management
Published in Eric Ford, Primer on Radiation Oncology Physics, 2020
Other systems supporting IGRT include the following: CyberKnife. Stereoscopic imaging (at intervals of approximately 1 second). See Section 9.2 and AAPM Task Group 135 (Dieterich et al. 2011).ExactTrac (Varian Inc./Brainlab Inc.). Stereoscopic X-ray imaging system coupled with a standard C-arm gantry linac. See AAPM Task Group #104 (Yin et al. 2009).Ultrasound guidance. Ultrasound probe is registered to the linac isocenter and used to guide treatment. This has found use in various forms over the years especially for prostate cancer treatments.Implanted electromagnetic (EM) transponder beacons (e.g. Calypso®, Varian Inc.). The transponders are miniature antenna coils in a glass envelope which can be implanted via catheter in tissue. An RF antenna array panel is placed just above the patient during treatment which allows for the real-time tracking of the position of the beacons during treatment.Surface imaging. Examples include AlignRT (Vision RT, London, UK) and C-RAD (C‐Rad AB, Uppsala, Sweden). For further information see AAPM Task Group 147 (Willoughby et al. 2012).
Magnetic Resonance Imaging
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The RF free induction signal (often referred to as just “the signal” here) is detected by the MRI scanner using a radio receiver. The receiving antenna consists simply of coils of wire placed near the body. The RF signal induces within the antenna time-changing voltage that can be measured to determine the frequency and magnitude of the free induction signal. Scanners have built-in receiving coils, but for some imaging applications, special receiving antennae are used. Surface coils, consisting of wires covered with plastic insulation and padding, are placed directly on the body over the parts of interest (Figure 8.13). These surface coils “listen in” only on broadcasting nuclei in a hemispherical region directly underneath. Their immediate proximity to the body allows them to more efficiently collect an RF signal to produce a better quality magnetic resonance image from superficially located tissues. We will return to this subject later when considering imaging applications.
Electrodes
Published in Jeffrey A Sherman, Oral Radiosurgery, 2020
A Perma-ground electrode is a passive electrode designed to eliminate the use of a visible passive electrode. The Perma-ground is a self-adhesive mylar strip which is adhered permanently to the back of the dental chair. It can be wired to the metal base of the chair which is usually connected to the grounding system of the office. The radiosurgical unit is also connected to this system. The radio signal is returned to the radiosurgical unit using the grounding system of the office. This form of antenna is in fact the most desirable system because it is permanently connected and creates no patient awareness or apprehension.
Electromagnetic pollution alert: Microwave radiation and absorption in human organs and tissues
Published in Electromagnetic Biology and Medicine, 2021
A half-wavelength 2.4 GHz dipole antenna and a half-wavelength 28 GHz dipole antenna are individually placed in front of a human organ or tissue model in an 80 mm (for the 2.4 GHz model) and a 20 mm (for the 28 GHz model) diameter spherical shape. The perfectly matched layer (PML) or open ‘add space,’ a specific CST name, set for the system boundaries, ensures the least reflected and scattered waves from the boundaries. The estimated reflected level is 0.0001% or 0.01%. The dipole antenna is assigned as Port 1, the transmitting port, 42.5 mm or 0.34λ (the 2.4 GHz dipole), and 10.7 mm or 1λ (the 28 GHz dipole) from the observation organ or tissue. The distance is chosen as an example of users holding or carrying a cellphone, tablet, wireless earbuds, smartwatch, etc., as well as to ensure a full-wave propagation. Figure 3 shows the physical domain of the 2.4 GHz and 28 GHz dipole set-ups with the dimensions and boundaries.
CardioMEMSTM System in the Daily Management of Heart Failure: Review of Current Data and Technique of Implantation
Published in Expert Review of Medical Devices, 2020
Muhammad Asif Mangi, Zeid Nesheiwat, Rehan Kahloon, George V. Moukarbel
The CardioMEMSTM HF system is indicated in patients with New York Heart Association (NYHA) class III HF with at least one HF related hospitalization in the previous year. The system consists of an implantable PA sensor, delivery system, patient or hospital electronic system and a patient database (Figure 1). The PA sensor is permanently placed in a PA branch during a right heart catheterization procedure. The sensor measures 3.5 mm in width, 2 mm in thickness, and 15 mm in length. It has a thin curved wire at each end and does not require any batteries or additional wires. The delivery system consists of a catheter, designed to release the PA sensor in the distal end of the PA. The patient and hospital electronic system include the electronic unit, antenna, and pillow. The antenna is paddle shaped and pre-assembled inside a pillow to make it easier and more comfortable for the patient to obtain readings. The electronic system receives wireless hemodynamic signals from the PA sensor and transmits them to the provider office, clinic, hospital or patient home. The PA sensor provides PA pressure waveform, PA pressures (systolic, diastolic and mean), and heart rate. Daily readings are sent to the healthcare provider. This information is transmitted to a secure website so that it could be accessed anytime via the internet. After analyzing the information from the PA sensor, and patient signs and symptoms, the provider may advise further dietary or lifestyle modification or optimize heart failure therapy.
Multiple antenna placement in microwave ablation assisted by a three-dimensional fusion image navigation system for hepatocellular carcinoma
Published in International Journal of Hyperthermia, 2018
Dezhi Zhang, Wenzhao Liang, Min Zhang, Ping Liang, Ying Gu, Ming Kuang, Feng Cao, Xiaoling Yu, Fengyong Liu, Jie Yu
Image-guided percutaneous microwave ablation (PMWA) therapy is a relatively new technology that was been developed in the 21st century [1–4]. PMWA therapy is minimally invasive, with results comparable to those of hepatectomy [5–9]. PMWA therapy has been most widely used for the ablation of hepatocellular carcinomas (HCCs) [10–12]. A high rate of recurrence seems to be a common problem. Several studies have shown that tumor size is an independent risk factor for tumor recurrence [11–14] because large HCCs need to be treated with a larger ablation necrotic area. If the tumor is larger than 3.0 cm in diameter, a single microwave antenna for ablation may not be sufficient. Therefore, several microwave antennae are necessary to ensure an effective treatment. The ablation thermal field should cover the tumor completely in three-dimensional (3D) space, while the surrounding vital structures, such as the bile duct, large blood vessels and gastrointestinal tract, should not be damaged.