J.M.S. Hutchison

Nuclear magnetic resonance pulse sequence and discrimination of high- and low-fat tissues

Abstract Signal size compared to independently measured T 1 is described for various pulse sequences on the Aberdeen Mk II nuclear magnetic resonance imager. The ability of these sequences to discriminate between certain tissue types, and in particular between adipose tissue and muscle, is discussed. Inversion recovery, with a t interval of 200 ms, gives the best discrimination for this purpose, with a contrast ratio of 6 between fat and muscle. Other image types, and especially T 1 , give better contrast for low-lipid soft tissues such as liver and spleen.

Instrumentation for NMR spin-warp imaging

Implementation of a new NMR imaging technique has lead to the introduction of new instrumentation in imaging machines. The authors describe magnetic field gradient drivers and microprocessor control circuits which have increased the versatility of the system. The performance of the imaging method and improved resolution whole body images are discussed.

Imaging by nuclear magnetic resonance and its bio-medical implications

The distribution of proton spin concentration (water concentration) and the proton spin-lattice relaxation time (T1) can be imaged in a sample by placing it in a magnetic field gradient, applying appropriate radio-frequency (rf) pulses, and measuring the rf radiated from the sample. The Aberdeen machine is designed to image the human body in vivo at 400 gauss and 1.7 MHz. The spatial resolution predicted is about 1 cm for a 20% difference of T1. Measurements of T1 for small samples of tissue in vitro show a five-fold range of values for some soft tissues. Breast tumours and liver metastases have shown T1 values very different from the surrounding tissue. The method has the potential of perhaps imaging any pathology which changes water concentration, forms fluid pools or affects the binding of water to macromolecules. The potential hazards, which need more investigation, seem slight.

Impedance imaging in upper arm fractures

We used the Aberdeen impedance imaging system to drive a constant current of 1 mA on a 10 kHz sine wave into the upper arm encircled by an elastic belt of 16 equi-spaced strip electrodes. The system was used to examine a normal upper arm, an upper arm with a recent humeral fracture and an upper arm with a clinically united fracture. We approximated the human upper arm to a circular cylinder and assumed bilateral symmetry of normal human limbs. We measured transverse limb resistivity ratios and reconstructed static two-dimensional images of the spatial distribution of log(resistivity) by the equipotential back projection technique using a homogeneous muscle equivalent saline reference. Our results indicate that impedance osteography provides unique information about the changing electrical characteristics at the fracture site. This information could prove a useful adjunct to clinical and radiological tests for fracture union.

NMR imaging — Method and applications

Spin and magnetic field Many nuclei exhibit the property of spin and hence possess a magnetic moment. The most commonly used nucleus in nuclear magnetic resonance (NMR) imaging is that of hydrogen, a single proton, which has a spin of l/2. In the absence of an external magnetic field the magnetic moments of the spins are randomly oriented but if a field is applied they align along the axis of this heId. Depending on the magnetic moment of the nucleus, the strength of the applied field (B) and the temperature of the system there is a small inbalance between the number of spins oriented ‘up’ and those oriented ‘down’ giving a net magnetization vector li? for the total spin system.

The Aberdeen phased array: a real-time ultrasonic scanner with dynamic focus.

A real-time ultrasonic scanner is described; it incorporates an electronic swept focusing process such that the image is optimally focused over a wide range of depths simultaneously. The scanner can be used to observe moving organs such as the heart, and internal detail is displayed on a grey scale image.

Pulse sequence and discrimination of high- and low-fat tissues

Signal size compared to independently measured T1 is described for various pulse sequences on the Aberdeen Mk II nuclear magnetic resonance imager. The ability of these sequences to discriminate between certain tissue types, and in particular between adipose tissue and muscle, is discussed. Inversion recovery, with a t interval of 200 ms, gives the best discrimination for this purpose, with a contrast ratio of 6 between fat and muscle. Other image types, and especially T1, give better contrast for low-lipid soft tissue such as liver and spleen.