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Biomedical subjects

R L Nicholson

Publications and source records attributed to R L Nicholson.

15 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↗
PubMed1988

Evaluation of parotid lesions by magnetic resonance imaging.

The effectiveness of magnetic resonance (MR) imaging in the evaluation of parotid lesions was tested by scanning 21 patients with parotid masses. In 20 patients the lesion was visualized, and in 19 benign/malignant differentiation was accurately made, indicating sensitivity and specificity of .95. The deep extent of the lesions was readily assessed by MR but the facial nerve could not be identified.

Adenoma↗
PubMed1986

Magnetic resonance imaging for detecting lesions of multiple sclerosis: comparison with computed tomography and clinical assessment.

Eighty-two patients with known or suspected multiple sclerosis (MS) were examined by means of magnetic resonance imaging (MRI) with a 0.15-T resistive scanner. The diagnosis could be made by MRI in 34 (97%) of the 35 patients with chronic, well-documented, stable MS and by high-volume delayed x-ray computed tomography (HVD CT) in only 6 (54%) of 11 patients in this group. The stage of the disease as judged from the MRI scans correlated poorly with the clinical status of the patient and with the known duration of the disease. MRI identified 28 (88%) of the 32 patients in whom MS was subsequently diagnosed by a neurologist, whereas regular contrast or HVD CT identified only 11 (52%) of 21 such patients. MRI is the most sensitive imaging modality for MS but is of little value in assessing the severity of the disease: many of the lesions seen on MRI scans are clinically "silent", and MRI does not usually detect small lesions in the brainstem, cerebellum or spinal cord that may be clinically significant.

Brain↗
PubMed1986

Dorsal midbrain syndrome in multiple sclerosis with magnetic resonance imaging correlation.

We describe the clinical characteristics and a series of magnetic resonance imaging (MRI) studies in a patient with the features of dorsal midbrain syndrome occurring in the setting of multiple sclerosis. A T2-weighted MRI study revealed a discrete abnormality in the tectum of the midbrain whereas a high volume delayed computed tomography (CT) scan was uninformative. In parallel with remission of the clinical findings, the MRI abnormality diminished over time and was no longer visible at one year suggesting that some MRI detected MS lesions can completely disappear with time. This report demonstrates the use of MRI to detect and to follow sequentially sites of known disease activity in MS.

Brain Diseases↗
PubMed1986

Comparison of respiratory triggering and gating techniques for the removal of respiratory artifacts in MR imaging.

Respiratory movement degrades magnetic resonance (MR) images of the chest and abdomen by increasing noise through the production of "ghost" artifacts and by decreasing edge sharpness in moving structures. Respiratory gating, which limits data acquisition to end-expiration, is successful in restoring edge sharpness and reducing ghosts but increases imaging time two to three times, which limits its use to sequences with short repetition times (TRs). To overcome this limitation, an alternative technique, respiratory triggering, was developed, which triggers the acquisition of an MR section at a fixed point on the respiratory cycle. This technique restores edge sharpness and reduces ghosts, but unlike gating, it can be used to produce an image at any phase of the respiratory cycle. Triggering requires long TRs since the TR is limited to the respiratory period (TP) or one-half of TP, depending on whether the same section is triggered once or twice during a single respiratory cycle. Gating and triggering were evaluated and compared for single-section and multi-section imaging of both volunteers and patients. The authors conclude that when a chest or abdominal survey is required, triggering takes less time than gating if TRs are required that exceed one-fifth of TP.

Abdomen↗
PubMed1986

Hazards and associated recommendations for Canadian MR imaging sites.

The recent national survey reported here indicates that the use of magnetic resonance (MR) imaging in Canada for medical diagnosis may rapidly become widespread. However, the technique involves a number of potential hazards to patients, operating staff and the general public. MR involves exposure to magnetic and radiofrequency fields which may have biological effects, indicating a need for guidelines on acceptable limits of exposure for both patients and operating personnel. Other hazards include effects on cardiac pacemaker function, effects on other medical equipment important for patient management, dislodgement of metallic surgical clips, induced heating of tissue or metallic implants, danger of ferromagnetic objects becoming projectiles and a risk of asphyxiation if a superconducting magnet quenches. The recommendations in the report are practical guidelines to minimize these risks and hazards.

Accident Prevention↗
PubMed1986

Magnetic resonance imaging: a review of basic principles and potential use in otolaryngology.

Magnetic Resonance imaging (MRi) is a new imaging technique. The authors review the basic principles and present several cases comparing MRi with CT scanning and surgical findings. The major advantages of MRi include lack of ionizing radiation, non-invasiveness and absence of interpetrous artifact when visualizing the posterior fossa. Magnetic Resonance imaging of the posterior fossa, especially of the brain stem and cranial junction, has significant advantages over imaging by CT scanning.

Adolescent↗
PubMed1985

Quantitation of lung water by nuclear magnetic resonance imaging. A preliminary study.

Pulmonary edema was produced in four anesthetized dogs by saline lavage. The animals were maintained by assisted ventilation with O2/halothane and examined by a nuclear magnetic resonance (NMR) 0.15T resistive-magnet imager. The distribution of edematous fluid was clearly observed. Image contrast increased with prolongation of the cycle time (TR). Tomographic maps of spin-lattice relaxation times (T1) of the lungs were calculated from the NMR images. Comparison of T1 values with gravimetric measurements of water content of lung samples showed significant correlation (r = .7, P less than .02, n = 12) suggesting a potential for in vivo lung water quantitation by NMR imaging. This in vivo correlation is qualitatively similar to the in vitro correlation. Accurate in vivo determinations of pulmonary T2 values may require respiratory gating.

Animals↗
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↗
PubMedDate not supplied

Nuclear magnetic resonance imaging, a new approach to the investigation of refractory temporal lobe epilepsy.

Nuclear magnetic resonance is a noninvasive technique of imaging the brain using signals produced by magnetic fields and radiowaves. Sixteen patients with refractory temporal lobe epilepsy (TLE) had magnetic resonance imaging (MRI) during investigation for possible surgical management. These images plus those of 10 normal controls, were interpreted blind and the results from the TLE patients compared to the EEG and computerized tomographic (CT) scan findings. Fourteen patients compared with one normal control had one or more of the following: small temporal lobe, small mesial temporal structures, small hemisphere, and focal mesial temporal prolonged spin-spin relaxation time. These findings correlated with the electrographically determined seizure focus in 11 patients. Enlarged or asymmetrical temporal horns were seen with equal frequency in patients and controls and did not correlate with the seizure focus. CT scans were less likely to show these changes than MRI. Correlation of the MRI changes with histopathology of resected temporal lobes was poor. MRI reveals structural and possibly functional alterations which may aid in the localization of the seizure focus in the temporal lobes of patients with refractory complex partial seizures.

Adolescent↗