Lowell Scott Smith

Signal, noise, and contrast in nuclear magnetic resonance (NMR) imaging

Calculations of the sensitivity of the saturation recovery and inversion recovery pulse sequences used in nuclear magnetic resonance imaging show the former to be superior in discriminating between tissues with the same proton density but different T1‘s. Two other pulse sequences, which are combinations of the above, have also been analyzed. These have lower T1 discrimination sensitivity, but other considerations, such as self-normalization, may still make them attractive. The calculations are only valid for selective excitation pulse sequences in which the selected slice profiles are approximately rectangular, and thus a sin(bt)/t radio frequency excitation is desirable. In order to ensure that the saturation recovery sequence gives valid results for pulse repetition times comparable to or shorter than T2 it is necessary to destroy the coherence between pulse applications. For this purpose we use a series of “spoiler” gradient pulses between pulse trains. The saturation recovery pulse sequence also has the advantage that, by the correct choice of interpulse spacing, sensitivity close to the optimum T1 discrimination can be achieved over a wide range of T1 values. This has the potential advantage to the clinician of simplifying his choice of parameters for imaging.

Fabrication of front surface matched ultrasonic transducer array

A slab of piezoelectric ceramic plated on all surfaces is bonded to quarter wavelength impedance matching layers of glass and plastic. The top surface of the ceramic is slotted and parallel cuts orthogonal to the slots are made through the ceramic and into the glass to delineate an array of elements each with a signal electrode between slots and a wrap-around ground electrode. After making ground connections and flying lead connections to the signal electrodes, the matching layers are fully cut through from the front. A covering or wear plate is attached to the front surface and a relatively large mass of acoustic damping material covers the backs of the elements.

Two-dimensional phased array of ultrasonic transducers

A two-dimensional ultrasonic phase array is a rectilinear approximation to a circular aperture and is formed by a plurality of transducers, arranged substantially symmetrical about both a first (X) axis and a second (Y) axis and in a plurality of subarrays, each extended in a first direction (i.e. parallel to the scan axis X) for the length of a plurality of transducers determined for that subarray, but having a width of a single transducer extending in a second, orthogonal (the out-of-scan-plane, or Y) direction to facilitate dynamic focussing and/or dynamic apodization. Each subarray transducer is formed of a plurality of sheets (part of a 2-2 ceramic composite) all electrically connected in parallel by a transducer electrode applied to juxtaposed first ends of all the sheets in each transducer, while a common electrode connects the remaining ends of all sheets in each single X-coordinate line of the array.

Radio-frequency spectrometer subsystem for a magnetic resonance imaging system

A radio-frequency (RF) spectrometer subsystem, for a nuclear magnetic resonance spectroscopy and imaging system, provides high-power RF pulse signals each having an envelope of minimum distortion; a portion of the actual RF magnetic field, in the sample-examination volume, is returned to the spectrometer for subsequent correction of the RF signal characteristics responsive to a comparison of the RF magnetic field sample waveform to the requested pulse envelope waveform.

Acoustic intensity monitor

A system and method are disclosed for monitoring the acoustic intensity of ultrasonic energy applied to a body by an ultrasonic probe for the purpose of diagnosing an internal target. The probe contacts a limited area of the body skin and a coupling medium, such as a coupling gel, is interposed to enhance acoustic coupling between the probe and the skin. A thermally sensitive agent in the coupling medium imparts color to the latter indicative of the heat dissipated on the skin area under the probe. Whenever a predetermined color change of the coupling medium indicates that the heat dissipation on this area exceeds a predetermined limit, the acoustic intensity of the ultrasonic energy beamed to the target is reduced.

Improved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors

The speed of sound varies with tissue type, yet commercial ultrasound imagers assume it is constant. Sound speed variation in abdominal fat and muscle layers is widely believed to be largely responsible for poor image contrast and resolution in some patients. The simplest model of the abdominal wall assumes that it adds a spatially varying time delay to the ultrasound wavefront. We describe an adaptive imaging system consisting of a GE LOGIQ 700 imager connected to a multi-processor computer. Arrival time errors for each beamforming channel, estimated by correlating each channel signal with the beamsum signal, are used to correct the imagers transmit and receive beamforming time delays at the image frame rate. A multi-row transducer provides two dimensional sampling of wavefront arrival time errors. After beamforming time delay correction, we observe significant improvement in abdominal images of healthy male volunteers, including increased contrast of blood vessels, increased brightness of liver tissue, and improved definition of the renal capsule and splenic boundary.

High-density cable and method therefor

A high-density cable of a type suitable for transmitting ultrasound signals from an ultrasonic probe to multiplexing circuitry during a medical ultrasound procedure is provided. The cable includes one or more flexible circuits arranged within a flexible sheath that surrounds and confines the flexible circuits. Each flexible circuit includes an elongate flexible substrate with oppositely-disposed surfaces and multiple conductors on at least one of these surfaces. The opposing longitudinal ends of the substrate define integral connectors for connecting with respective output connectors and/or electronic devices, such as an ultrasonic probe or multiplexing circuitry.

Method of making a two dimensional ultrasonic transducer array

An improved two-dimensional ultrasonic transducer array is provided by forming a plurality of elongated transducer strips each including a central body of piezoelectric material having mounted thereon a conducting inner matching layer and outer matching layer, a conducting inner backing layer and a nonconducting lossy outer backing layer, depositing a conducting film on the outer surface and one side surface of the outer matching layer and into electrical contact with the conducting backing layer of each strip and depositing a plurality of conducting films in space relation to one another on the back surface and one side surface of the lossy backing layer and into electrical contact with the conducting backing layer to provide an electric circuit to the front and back faces of the piezoelectric layer. The strips are then assembled in spaced parallel relation with insulating strips bonded therebetween, and grooves are cut transversely of the transducer strip through the matching layers, the piezoelectric layer, the inner backing layer and into but not through the lossy backing layer to thereby provide an array of individual transducers arranged in spaced parallel rows with conducting films extending from the face and back surfaces of each transducer to provide an independent electrical circuit to each transducer in the array.

A 1.5D transducer for medical ultrasound

The current shift to digital beamforming technology holds promise for regular and rapid increases in the number of channels in a medical imager. A 1D transducer typically utilizes 125 elements, while a fully sampled two-dimensional aperture requires of order 10000 elements. Currently, channels are still expensive, so it is of interest to evaluate how much performance can be improved with a moderate increment in channel count. How may we maximize the impact on voxel size? The number of elevational elements is constrained by how complex the interconnections can become. It is impractical to significantly degrade the azimuthal resolution from the 1D case. We present beam profiles and images from a first attempt at judicious use of a 256 channel imager. Simulations and experiments allow us to explore compromises among a number of design goals. We have fabricated a transducer with several elevational rows which reduces the slice thickness of the image while maintaining full azimuthal resolution

7.5 MHz pediatric phased-array transesophageal endoscope

This work extends the clinical benefits of phased array transesophageal echocardiography (TEE) with high detail and contrast resolution to include neonatal patients. We have built several prototype 64 element, 7.5 MHz phased array transducers housed in 6.2 mm endoscope shafts for use with commercially available imaging systems. The acoustic design is standard, but the miniaturized packaging of the electrical connections was quite challenging. The endoscopes demonstrate very good structural resolution and excellent sensitivity for color flow imaging and CW Doppler. They have been used on patients as small as 1.9 kg, frequently as an anatomical guide during catheter based interventions and during congenital-heart surgery. Array test data and representative clinical studies are shown