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Biomedical subjects

R L Nicholson

Publications and source records attributed to R L Nicholson.

6 recordsLinked to original sources
PubMed1992

Correction for attenuation in technetium-99m-HMPAO SPECT brain imaging.

We present a correction technique that uses the effective bone and tissue attenuation coefficients to compensate 99mTc-HMPAO brain SPECT projections for attenuation. Transverse images of a human skull filled with a uniform mixture of 99mTc and gelatin have a greater count density at the center with respect to the periphery when corrected for attenuation with the effective water/tissue coefficient of 0.12 cm-1. An attenuation coefficient of 0.09 cm-1 produces uniform images at the expense of a reduced count density. Additional experiments with phantoms wrapped with aluminum (to simulate bone) indicate that the greater count density at the image center is a result of increased attenuation at the edges of the projections where there is a greater path length through the aluminum (or bone). SPECT projections explicitly corrected for both bone and soft-tissue attenuation result in images of improved uniformity and increased count density.

Brain↗
PubMed1991

A prospective study of magnetic resonance imaging in lymphoma staging.

In this prospective study, magnetic resonance imaging (MRI) was compared with computed tomography (CT) in patients with non-Hodgkin's lymphoma (NHDL), and with CT and laparotomy in patients with Hodgkin's disease (HD). Among 31 patients with NHDL, there was agreement between MRI and CT findings in 21 patients; MRI findings were positive and CT findings were negative in 8 patients; and MRI findings were negative and CT findings were positive in 2 patients. The false-negative findings of MRI included a laparotomy-proven mesenteric mass and a 6.6-cm lesion in the spleen, both shown by CT. In 13 evaluable patients with HD, there was agreement between MRI and laparotomy findings in 8 patients; MRI findings were positive and laparotomy findings were negative in 4 patients; and MRI findings were negative and laparotomy findings were positive in 1 patient. CT findings agreed with laparotomy findings in nine patients; CT findings were positive and laparotomy findings were negative in one patient: and CT findings were negative and laparotomy findings were positive in three patients. This suggested that MRI, although more sensitive than CT, was less specific with more false-positive findings. The spin-lattice relaxation time (T1) for the spleen was generally higher in patients with HD who had pathologically confirmed splenic involvement, and tended to increase with increasing spleen weight. This study was performed on a prototype 0.15 Tesla (Technicare Inc., Solon, OH) resistive unit at a time when methods and reporting for MRI were still being developed. Although MRI appears to have fewer false-negative findings than CT in evaluating the abdomen of lymphoma patients, the lack of a gastrointestinal contrast agent and specificity of T1 elevations in the spleen would not suggest that MRI could replace CT or laparotomy as a staging technique.

Adolescent↗
PubMed1991

Reverse oblique reconstruction for SPECT of the spine.

Anatomic localization of spine lesions, shown by Tc-99m phosphonate SPECT, to facet joint or pedicle is often difficult due to limitations in resolution. Indirect localization, relating lesion position on sagittal reconstruction to the adjacent visible vertebral bodies and also to patient spine radiographs, might be required. Some laterally placed lesions, however, cannot be visualized in the more midline slices showing the vertebral bodies. Oblique tomographic reconstruction overcomes this limitation.

Adolescent↗
PubMed1979

CT anatomy of the nasopharynx, nasal cavity, paranasal sinuses, and infratemporal fossa.

Analysis of anatomical features of the nasopharynx, nasal cavity, paranasal sinuses, and infratemporal fossa was carried out by retrospective review fo 50 CT scans. Conventional and axial anatomy are discussed, and normal size limits of selected structures are proposed on the basis of a series of measurements. Examples of early and advanced disease are shown.

Humans↗
PubMed1977

Persistent primitive sciatic artery.

Angiography revealed persistence of the primitive sciatic artery in two cases. In one, the artery supplied a large arteriovenous malformation, and the profunda femoris artery was absent. In the other, there were associated findings of neurofibromatosis, decreased left lower limb lymphatic vessels, a left subinguinal lymphocele, and absent external iliac and femoral arteries.

Adult↗