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Transmission Electron Microscopy

Transmission Electron Microscopy

In 1931, physicist Ernst Ruska—building on the idea that magnetic fields can direct an electron beam just as lenses can direct a beam of light in an optical microscope—developed the first prototype of the electron microscope. This development led to the development of the field of electron microscopy. In the transmission electron microscope (TEM), electrons are produced by a hot tungsten element and accelerated by a potential difference in an electron gun, which gives them up to 400...

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Related Experiment Video

Updated: Apr 30, 2026

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Published on: May 9, 2014

Electron contamination modeling and reduction in a 1 T open bore inline MRI-linac system.

B M Oborn¹, S Kolling², P E Metcalfe³

¹Illawarra Cancer Care Centre (ICCC), Wollongong, NSW 2500, Australia and Centre for Medical Radiation Physics (CMRP), University of Wollongong, Wollongong, NSW 2500, Australia.

Medical Physics

|May 3, 2014

Summary

An electron contamination deflector (ECD) and helium gas region effectively reduce skin dose in MRI-linac systems. This technology minimizes electron contamination focusing, a potential side effect that increases radiation dose to the skin.

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Last Updated: Apr 30, 2026

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Area of Science:

Medical Physics
Radiation Oncology
Magnetic Resonance Imaging

Background:

Inline MRI-linac systems integrate magnetic resonance imaging (MRI) with linear accelerators (linacs).
A potential side effect is electron contamination focusing, leading to elevated skin dose.
This study investigates mitigation strategies for an open bore 1 T MRI system.

Purpose of the Study:

To model the efficiency of an electron contamination deflector (ECD) in purging electron contamination.
To assess the impact of a helium gas region on reducing air-generated contamination.
To reexamine skin dose predictions for an open bore 1 T MRI system.

Main Methods:

3D magnetic field maps were generated using magnetic modeling of the 1 T MRI.
Geant4 Monte Carlo simulations were performed, incorporating linac head, ECD, and water phantom.
2D skin doses at 70 μm depth were calculated for various beam sizes and field configurations.

Main Results:

The ECD was highly efficient at purging electron contamination, though some scattering occurred.
Using helium gas significantly minimized air-generated contamination.
An optimal ECD and helium gas combination moderately increased skin dose in small hot spots (12-65% of Dmax).

Conclusions:

An efficient ECD coupled with a helium gas region can ameliorate skin dose increases in MRI-linac systems.
The ECD is practical, with correctable MRI imaging distortion and manageable mechanical forces.
This approach offers a viable solution to mitigate electron contamination side effects in MRI-guided radiotherapy.