Date of Award

Spring 1987

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Heinen, James A.

Second Advisor

Schaefer, Daniel J.

Abstract

Within the last decade, Magnetic Resonance, MR, has been developed into a diagnostic tool for medical imaging. Similar to Computed Tomography or CT scanners, the MR scanner is capable of viewing living human anatomy without surgery or other invasive probes. Imaging with MR is useful for diagnosing diseases of the brain, spinal column, joints, heart, and abdomen to name a few. In the past, X-ray technology had to diagnose most of the diseases, but now the radiologist can use MR to distinguish not only density of tissue but also chemical composition of the tissue. MR provides another window into the human body but not without several drawbacks. At present, most clinical applications of MR require over several minutes of data collection to produce images. Since the MR process is highly susceptible to motion of the patient, they are instructed to lie as still as possible throughout the scan. Of course the patient's cardiac and respiratory systems function as they normally would. If this involuntary motion is not compensated, then the image contains noncoherent noise that is superimposed over the motionless anatomy. Due to the manner in which data is collected, the signal coming from the heart tissue is reconstructed into bands of noise that extend outside of the body image. A solution to this problem is a faster data collection that lasts only a fraction of the total cardiac cycle. However, this method produces a poorer quality image with low contrast between different types of tissue. Another solution is cardiac gating which synchronizes the data acquisition with the cardiac cycle. The common approach for cardiac gating uses the electrocardiogram. However, the use of ECG in MR is plagued by artifacts induced by the static Magnetic field and body motion, by the gradient (extremely low frequency) magnetic fields, and by the radio frequency fields. In addition, ECG instrumentation must be carefully designed to avoid patient hazards and setup time is lengthy. This thesis explores an alternative cardiac gating method that uses non-contact ultrasound technology for proximity detection. Two ultrasound transducers that are suspended above the surface of the body are used to measure the displacement of the carotid artery at the surface of the neck. The cardiac cycle is measured at the carotid pulse and converted to a gating signal for MR imaging...

Download

Share

COinS

Restricted Access Item

Having trouble?