Birdcage volume coils and magnetic resonance imaging: a simple experiment for students

Abstract

Background: This article explains some simple experiments that can be used in undergraduate or graduate physics or biomedical engineering laboratory classes to learn how birdcage volume radiofrequency (RF) coils and magnetic resonance imaging (MRI) work. For a clear picture, and to do any quantitative MRI analysis, acquiring images with a high signal-to-noise ratio (SNR) is required. With a given MRI system at a given field strength, the only means to change the SNR using hardware is to change the RF coil used to collect the image. RF coils can be designed in many different ways including birdcage volume RF coil designs. The choice of RF coil to give the best SNR for any MRI study is based on the sample being imaged. Results: The data collected in the simple experiments show that the SNR varies as inverse diameter for the birdcage volume RF coils used in these experiments. The experiments were easily performed by a high school student, an undergraduate student, and a graduate student, in less than 3 h, the time typically allotted for a university laboratory course. Conclusions: The article describes experiments that students in undergraduate or graduate laboratories can perform to observe how birdcage volume RF coils influence MRI measurements. It is designed for students interested in pursuing careers in the imaging field.

Three‐dimensional NMR microscopy of zebrafish specimens

“…Substituting the VC20 RF coil by a VC10 RF coil one would expect a signal to noise ratio (SNR) improvement by a factor of approximately 2 . However, in our own measurements of SNR in an FFPE specimen at 58°C and our calibration of RF power at 21°C with an FF specimen, we found an improvement of about 2.5‐fold.…”

A Review on the RF Coil Designs and Trends for Ultra High Field Magnetic Resonance Imaging

“…It defines the number of resonance modes that the BC coil can operate, given by (N/2) + 1 (67). The magnetic field produced by the BC coil is intrinsic LP; however, it is possible to produce circular polarization by means of quadrature excitation, which increases the S/N by a factor of √2 (68)(69)(70). BC coils can produce uniformly distributed RF magnetic fields with a high S/N if the current in the N legs is distributed as follows:…”

A study on multiple array method of birdcage coils to improve the signal intensity and homogeneity in small‐animal whole‐body magnetic resonance imaging at 7 T

“…13 Increasing the number of rungs can improve the jB 1 j-field sensitivity, but self-inductance coupling can result in jB 1 j-field interaction. 19,20 For a 7-T MR system operating at a frequency of 300 MHz, the physical wavelength is 1 m in free space, and the effective RF wavelength is rapidly reduced to 12.5 cm when a specific subject is loaded. 15 In general, the diameter of a BC coil for an animal is much smaller than that for a human; therefore, the capacitor value is larger.…”

“…18 The diameter-to-length ratio of the BC coil affects the uniformity of the magnetic field and the sensitivity of the signal and, therefore, must be optimized. 19,20 For a 7-T MR system operating at a frequency of 300 MHz, the physical wavelength is 1 m in free space, and the effective RF wavelength is rapidly reduced to 12.5 cm when a specific subject is loaded. If the BC coil configuration exceeds the effective RF wavelength value, the coil performance diminishes.…”