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Biomedical subjects

D Plewes

Publications and source records attributed to D Plewes.

11 recordsLinked to original sources
PubMed1988

Fat-suppression MR imaging of the orbit.

The effect of fat suppression on orbital MR imaging was tested by using a derivative of the Dixon method called chopper fat suppression in eight normal volunteers and eight patients with normal conventional orbital MR studies. Chopper fat suppression requires no postacquisition image processing or increased scan time and can be applied through a wide range of T1 to T2 weighting. In normal orbits, fat suppression was found to be advantageous for imaging the lacrimal gland and the optic nerve. Using fat-suppressed T1- or intermediate-weighted sequences, 2000/30 (TR/TE), the optic nerve was recognized by its high signal intensity relative to adjacent CSF, dural sheath, and surrounding fat. The technique minimized loss of anatomic detail by reducing chemical shift misregistration artifact. Disadvantages included an overall lower orbital signal/noise ratio. When used in conjunction with a TR/TE combination carefully selected for both anatomic region of interest and suspected pathology, the fat-suppression technique has the potential for improving the visualization of orbital lesions.

Adult↗
PubMed1978

Edge contrast in ionography.

The effect of Mylar foil thickness on the appearance of ionography images has been investigated. Approximate expressions for the depletion width of strips and halfplanes of charge are given with supporting experimental measurements. In microdensitometer traces of charged strips and halfplanes the density is shown to be proportional to the vertical field profile of the charge pattern near the Mylar. This work suggests a simple means of altering edge contrast for ionography by using different thicknesses of Mylar. Ionography images of a hand phantom illustrate this effect.

Radiographic Image Enhancement↗
PubMed1975

New methods of imaging in diagnostic radiology.

The basic ideas of electrostatic imaging with special reference to ionography are reviewed. The concept of edge contrast is explained in terms of calculated powder particle trajectories and methods for controlling edge contrast are presented. Also, methods for reading a foil from outside the ionography chamber using the electric field extending through the foil are described. An example of an image taken with liquid in the chamber (liquid lonography) is presented, and the possible extension of liquid ionography to nuclear medicine is discussed.

Absorptiometry, Photon↗
PubMedDate not supplied

SAR reduced pulse sequences.

Three techniques were considered for reducing the RF (radiofrequency) power deposition in the body while maintaining scan time efficiency: reducing the RF peak amplitude while increasing the pulse width, substituting gradient echoes for spin echoes, and reducing the flip angle of the phase reversal pulse. The use of gradient echoes was found to be the most efficient means to reduce the power delivered to the patient and to obtain rapid data acquisition. The effect upon SAR (specific absorption rate) and SNR (signal-to-noise ratio) was demonstrated on a phantom when the phase reversal pulse was reduced from the standard 180 degrees to 90 degrees. Data in the body indicated a fairly constant SNR down to a refocusing flip angle between 110 degrees and 135 degrees. An initial clinical evaluation was performed at three institutions using the method of reducing the flip angle of the phase reversal pulse. The scan with theta = 120 degrees was rated by readers in a blinded study as having acceptable diagnostic image quality while the 135 degrees scan had comparable image quality to a conventional 90 degrees - 180 degrees pulse sequence. The use of reduced phase reversal pulses was seen as an efficient protocol to obtain T1-weighted images at rapid data rates while reducing the power delivered to the body by about 40%.

Humans↗
PubMedDate not supplied

Electrostatic fields in ionography.

There is renewed interest in diagnostic radiology in electrostatic methods of imaging, such as xeroradiography and ionography. This is due to the fact that edge contrast can be achieved, aiding in the visualization of soft tissue tumors. In analyzing the image forming properties of these system, we chose to solve the electrostatic problems by the method of images. We present methods and recursion formulas for calculating electrostatic fields due to (a) any charge distribution on a slab of dielectric (the solution involves a single infinite series) or (b) the same as the above with the introduction of an additional ground plane parallel to the dielectric surface (the solution now involves double infinite series). Analysis of these fields suggests new methods of controlling edge contrast and development configurations where the field which penetrates through the foil is used to produce the final image rather than the field above the charged surface.

Electric Conductivity↗
PubMedDate not supplied

Theoretical and experimental determination of sensitivity and edge enhancement in xeroradiography and ionography.

A study of the factors affecting image quality and x-ray sensitivity of ionography and xeroradiography is presented. First, the relative charge sensitivities (nC/cm2mR) are compared. It is shown that high pressure xenon (10 atm cm) as used in ionography produces more than 2.5--3.5 times more charge than the selenium layers used in xeroradiography for the same x-ray exposure. The influence of development time and toner deposition on the appearance of images is investigated theoretically and experimentally. A parameter describing development sensitivity is proposed. It is shown that an increase in development sensitivity (ODcm2/nC) with increasing development time is accompanied by a loss in edge enhancement. The development sensitivity of ionography is about twice that typical of xeroradiography. This makes the total sensitivity (OD/mR) or the ionography process more than 4.5--6.5 times that of xeroradiography. The total sensitivity of ionography is about 1/2 that of par speed film screen combinations.

Polyethylene Terephthalates↗