Biomedical subjects

M K O'Connor

Publications and source records attributed to M K O'Connor.

At least 19 recordsLinked to original sources

PubMed1996

Instrument- and computer-related problems and artifacts in nuclear medicine.

Advances in gamma-camera design over the last 5 to 10 years have improved all aspects of image quality, particularly for tomographic imaging. As system complexity increases, it becomes more important that both the technologist and physician be able to recognize the various types of artifacts that can occur in gamma-camera systems and their potential impact on clinical studies. A thorough evaluation of the system at installation and a comprehensive quality control program will detect most problems that can occur. The most sensitive indicator of gamma-camera performance is uniformity. Because this measurement is performed on a daily basis, it is the principle tool in evaluating the status of the gamma-camera. Most artifacts related to the integrity of the detector head, computer system, and hard copy device can be detected on the uniformity image. For tomographic imaging, a quantitative determination of uniformity is needed to ensure that the system will not introduce ring artifacts into the patient data. Unlike planar imaging, the complex nature of tomographic imaging requires additional checks on system performance to ensure that other components of the system, such as the collimator, gantry, and imaging table, are not a source of artifact in the reconstructed image data. Failure of a system component can occur at any time and may be subtle and difficult to recognize in modern systems. In such an environment it becomes imperative that any unexpected finding in a clinical study be questioned with respect to a possible malfunction of some aspect of data acquisition and analysis.

Artifacts↗

PubMed1996

Technical pitfalls in image acquisition, processing, and display.

Optimal image quality is an ideal in nuclear medicine that is not always realized, being subject to a variety of conditions that can act, either singly or in combination, to undermine its accomplishment. These conditions include potential defects and limitations in both the hardware and software used for the acquisition and reconstruction of nuclear medicine images. Factors relating to individual patients can contribute to these obstacles, including limitations in mobility and compliance. Importantly, suboptimal or erroneous technique is a common source of poor imaging results, with loss of diagnostic efficacy. Appropriate test selection and careful attention to patient preparation and procedural details are essential elements in avoiding image flaws and artifacts in nuclear medicine.

Artifacts↗

PubMed1996

Patient-related pitfalls and artifacts in nuclear medicine imaging.

Quality control in nuclear medicine is all important. This applies not only to preparation of the patient and acquisition of the image, but also to interpretation of the study. Although it may seem self-evident, it is important to remain aware of artifacts that are directly related to the patient and need special consideration. Furthermore, at times the distinction between normal variants and artifacts can be difficult. Commonly encountered patient-related artifacts include artifacts caused by attenuation, contamination artifacts, and artifacts caused by intravenous lines, tubes, and catheters. Less commonly, artifacts arise because of the use of multiple isotopes, the presence of fistulas or surgically altered anatomy, and pharmaceuticals and other substances interfering with expected radiopharmaceutical uptake and distribution. The diagnostic accuracy of nuclear medicine reporting can be improved by awareness of these patient-related artifacts. Both awareness and experience are also important when it comes to detecting and identifying normal (and abnormal) variants.

Artifacts↗

PubMed1996

Hyperventilation alters colonic motor and sensory function: effects and mechanisms in humans.

UNLABELLED: BACKGROUND & AIMS. Hyperventilation-induced hypocapnia affects hemodynamic function and enhances colonic motility. The aims of this study were to determine the effects of hypocapnic hyperventilation on colonic motility and sensation in health and to explore the putative neurohumoral mechanisms. METHODS: In experiment 1, colonic tone, sensation, plasma levels of cortisol, beta-endorphin, selected gut neuropeptides, norepinephrine, epinephrine, and splanchnic blood volume were measured during two sequences of hypocapnic hyperventilation. In experiment 2, colonic tone and sensation were assessed during eucapnic hyperventilation and abdominal compression. RESULTS: Hypocapnic hyperventilation, but not eucapnic hyperventilation or abdominal compression, significantly increased colonic tone and sensitivity to balloon distention (P = 0.017) without altering humoral mediators or splanchnic blood volume. Plasma norepinephrine level increased (P = 0.017) and splanchnic blood volume decreased (P = 0.028) during 5 minutes after hyperventilation, consistent with homeostatic responses. CONCLUSIONS: Increased colonic tone and sensation during hypocapnic hyperventilation are not caused by colonic compression. These effects of hyperventilation are not mediated humorally but may result from direct metabolic effects of hypocapnia on colonic muscle or from changes in central autonomic control of colonic smooth muscle.

Adult↗

PubMed1996

Single photon emission computed tomography brain imaging.

SPECT brain perfusion imaging has definite value in the evaluation of cerebrovascular disease (particularly acute stroke), dementia, epilepsy, and may have a role in the diagnosis of brain death and head trauma. SPECT with tumor tracers T1-201 and Tc-99m sestamibi shows promise for detecting tumor recurrence.

Brain↗

PubMed1995

Effects of scatter correction on the measurement of infarct size from SPECT cardiac phantom studies.

UNLABELLED: Thallium-201 and 99mTc-sestamibi images of the heart contain a significant amount of scattered events which degrade image quality. Newer generation gamma cameras exhibit enhanced energy resolution and hardware/software to perform scatter correction. The principal aim of this study was to evaluate the effects of these advances in instrumentation on the quantitation of defect size from tomographic images of the heart obtained from a cardiac phantom. METHODS: Tomographic images of a cardiac phantom containing no defect and defects of 5%-70% of total myocardial mass were acquired both with and without scatter correction for 201Tl and 99mTc studies. Data were acquired on a newer generation gamma camera with an energy resolution of 8.7% at 140 keV. From conventional short-axis slices of the heart, circumferential count profiles were generated from five representative slices. Defect size was computed from the fraction of radians that fell below a fixed threshold value in each of the five count profiles. The nadir value (min/max) of the count profiles in each study was used as an index of image contrast. RESULTS: For both 201Tl and 99mTc, threshold values between 55%-60% gave the best correlation (r > 0.99), with the lowest average absolute error in estimating defect size (< 2.1%). Scatter correction reduced the average absolute error to 0.8% for 99mTc and 1.4% for 201Tl, significantly reduced the nadir values for both isotopes (p < 0.0001 for both 201Tl and 99mTc and led to a marked improvement in image quality for both tracers. CONCLUSION: Scatter correction reduces the error associated with measurement of infarct size, increases image contrast and improves image quality for both 201Tl and 99mTc, as assessed in a phantom model.

Gamma Cameras↗

PubMed1995

Particulate silicone for use in periurethral injections: local tissue effects and search for migration.

We examined the histologic behavior and migratory tendencies of a silicone-based injectable paste (Macroplastique) with potential application in treating urinary incontinence. Thirteen female dogs were studied. Six received 2 periurethral injections of large-particle paste, with a median diameter of 110 microns, and 7 received similar injections with small-particle paste (median diameter, 73 microns). The paste was radiolabeled with cobalt-57. Histologic analysis was performed at 4 or 9 months. The pathologic appearance revealed intact large-particle injection sites. The small-particle sites had dissipated significantly. This was confirmed by nuclear imaging. Large particles produced an encapsulated fibrous sheath without local migration. There was a histiocytic reaction within the injection site but no granuloma formation. Distant migration was observed in 1 dog (short term, large particle), without an inflammatory response. Migration of silicone occurred locally and distantly in animals that received small particles. X-ray microanalysis confirmed the presence of silicone particles.

Animals↗

PubMed1995

Effects of tomographic table attenuation on prone and supine cardiac imaging.

UNLABELLED: The purpose of this study was to determine the attenuation characteristics of tomographic imaging tables and to evaluate these effects on prone and supine imaging of the heart, using a cardiac phantom. METHODS: Table attenuation as a function of imaging angle was measured in seven different types of tomographic imaging tables, by imaging 99mTc and 201TI line sources placed at various distances above the center-line of the table. Three imaging tables exhibiting low, medium and high attenuation were further studied using a cardiac phantom filled with 201TI to see the effects of attenuation on myocardial image quality. Studies were performed under three conditions: no table, table above phantom (prone imaging) and table beneath phantom (supine imaging). Circumferential count profiles were generated from short-axis slices of the myocardium. RESULTS: Most SPECT tables attenuated only 5%-10% (99mTc) and 8%-12% (201TI) at an angle of 180 degrees (face of detector parallel to table). At angles of 90 degrees and 270 degrees, however, table attenuation was highly dependent on the tables' design and material content. From the cardiac phantom studies, short-axis circumferential count profiles showed no significant difference for low-attenuation tables and a slight difference (< 5%) in the septal region for medium-attenuation tables. In prone imaging, high-attenuation tables caused a reduction in counts in the antero-lateral wall (> 10%) and in the septum (> 5%). CONCLUSION: Table attenuation characteristics should be considered when comparing studies from different systems and in establishing a normal database for 201TI polar maps. High-attenuation tables should be used with caution in cardiac studies.

Heart↗

PubMed1995

Quantitative myocardial SPECT for infarct sizing: feasibility of a multicenter trial evaluated using a cardiac phantom.

UNLABELLED: This study determined the feasibility of performing a multicenter trial using quantitative SPECT myocardial perfusion imaging in patients with acute myocardial infarction. The feasibility was assessed by a cardiac phantom. METHODS: Twenty-two gamma camera systems in 19 laboratories were evaluated. Each laboratory performed nine studies on the cardiac phantom and performed quality control tests of system uniformity, collimator quality and gantry alignment on their gamma camera system. Defects simulating "hypoperfused" myocardium of differing amounts were placed in the myocardium for eight of the nine studies. Measured defect size was compared to true defect size. RESULTS: A total of 198 studies from 22 systems were analyzed. Three studies were technically inadequate. For all 22 systems, the average correlation coefficient between true and measured defect size was 0.992 +/- 0.009, with a range from 1.00 to 0.97. Three systems were rejected due to slopes of the regression line outside the limits 1.00 +/- 0.10 and mean errors > 5% in estimating defect size. The remaining systems had a correlation coefficient of 0.995 + 0.008 with an average slope of 1.00 +/- 0.04 and an intercept of 0.11% +/- 1.57%. The mean error in estimating defect size was 2.08% +/- 0.69%. CONCLUSION: The small interlaboratory variation and the close correlation with true defect size observed in a cardiac phantom indicate the feasibility of quantitative myocardial SPECT as a useful tool in multicenter trials evaluating therapy in acute myocardial infarction. Preliminary objective testing is required, however, to identify systems with technical deficiencies.

Feasibility Studies↗

PubMed1995

Single photon emission computed tomography.

Single-photon emission computed tomography is a well established functional imaging technique in epilepsy that aids precise noninvasive localization of the seizure focus required for surgical intervention in refractory seizures. Electroencephalography with video monitoring of seizures precedes more invasive evaluation, such as cortical or depth electrodes. Positron emission tomography studies in temporal lobe epilepsy are moderately sensitive, demonstrating ipsilateral hypometabolism. Ictal single photon emission computed tomography studies in temporal lobe epilepsy demonstrate transient intense hyperemia in the anterior temporal lobe structures. Peri-ictal images show persisting mesial temporal hyperperfusion with lateral hypoperfusion developing over the next 2 to 5 minutes to be replaced by significant hypoperfusion in the postictal phase. Interictal single photon emission computed tomography with ipsilateral hypoperfusion, suffers from reduced sensitivity and accuracy, whereas ictal and, to a lesser extent, peri-ictal and postictal single photon emission computed tomography are highly sensitive and accurate in localizing temporal lobe epilepsy. New iodinated neuroreceptor single photon emission computed tomography imaging agents hold promise in localizing the seizure focus (focally reduced uptake) without ictal injection, and also may elucidate underlying mechanisms inherent to epilepsy.

Cerebrovascular Circulation↗

PubMed1994

Effect of viscosity on oropharyngeal and esophageal emptying in man.

The effect of bolus viscosity on oropharyngeal and esophageal emptying is not known. We investigated this question in 38 healthy volunteers by measuring the transit of five semisolid boluses of varying viscosities across the oropharynx and the esophagus with the aid of scintigraphy. The studies were performed twice on consecutive days. The results show that oropharyngeal and esophageal emptying are reliably reproduced from day to day. Esophageal emptying was inversely related to bolus viscosity; however, oropharyngeal emptying was not influenced by bolus viscosity. We conclude that bolus viscosity has significant, but selective, effect on oropharyngoesophageal emptying.

Adult↗

PubMed1994

The radiation dosimetry and normal value study of 99mTc-HMPAO-labeled leukocytes.

RATIONALE AND OBJECTIVES: Indium-111 (111In)-labeled leukocyte scanning has been used frequently in patients suspected of having infections. Recently, technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) has been used to label leukocytes. This study was undertaken to determine the distribution and dosimetry of 99mTc-HMPAO leukocytes in healthy subjects. METHODS: Five healthy volunteers had leukocytes labeled with 99mTc-HMPAO. After injection of the labeled leukocytes, whole body images and blood and urine samples were obtained at multiple time points. RESULTS: Visual interpretation of the images demonstrated significant bowel activity as early as 2 hours and increasing with time such that one the 8- and 24-hour images, the amount of bowel activity would preclude using 99mTc-HMPAO leukocyte scanning for abdominal processes. The dosimetry for this study is similar to that of other studies and is in an acceptable diagnostic range. CONCLUSIONS: 99mTc-HMPAO leukocyte studies are an acceptable alternative to 111In-labeled leukocyte studies in terms of dosimetry. Use of such studies in the abdomen should be limited to early images, usually before 2 hours, to avoid confusion with the normal route of excretion in the bowel.

Female↗

PubMed1994

Parathyroid imaging with technetium-99m-sestamibi: an initial institutional experience.

BACKGROUND: The ideal method for preoperative localization of abnormal parathyroid glands has yet to be determined. Technetium-99m-sestamibi, previously used for myocardial perfusion studies, has recently been introduced for parathyroid imaging. METHODS: From August 1991 to September 1993, 44 patients underwent Tc-99m-sestamibi scanning (45 scans) and surgical exploration for hyperparathyroidism at our institution. These 44 patients form the database for this retrospective study. Twenty-eight patients had persistent hyperparathyroidism, six had recurrent disease, three had prior thyroid operation, and seven underwent first time neck operations. The nature of disease was complex and varied: single gland, 26; primary hyperplasia, 5; multiple endocrine neoplasia type 1, 5; familial, 3; secondary or tertiary, 5. One patient with single gland disease and one patient with multiple endocrine neoplasia type 1 had parathyroid carcinoma. All patients had biochemical confirmation of hyperparathyroidism. RESULTS: Twenty-six (58%) of 45 scans accurately predicted the location(s) of all abnormal gland(s) involved (true positive). Surgical removal of these glands was curative. Sixteen (36%) of 45 scans were false negative because they did not show all abnormal glands involved; however, 7 of these 16 scans did localize at least one abnormal gland. The overall sensitivity of this test was 62% when all abnormal glands were considered but increased to 79% with the demonstration of at least one abnormal gland. These values increased to 80% and 90% (p = 0.03), respectively, in the last 20 patients when the injected dose of Tc-99m-sestamibi was increased from 10 to 15 mCi. Thirty-seven of 44 patients were cured after operation. Six of the seven patients who experienced surgical failure had multigland disease, one of which was malignant. Sestamibi scans correctly identified abnormal cervical glands in 18 (58%) of 31 patients and abnormal mediastinal glands in six (75%) of eight patients. CONCLUSIONS: Tc-99m-sestamibi scanning is helpful in the reoperative setting as an adjunct to localizing abnormal parathyroid tissue. A higher percentage of positive tests occurs in patients with mediastinal and single gland disease. A higher dose of Tc-99m-sestamibi (15 mCi) significantly improves test sensitivity.

Adult↗

PubMed1993

Nonspecific motor disorder of the esophagus: a real disorder or a manometric curiosity?

BACKGROUND: Nonspecific esophageal motility disorder (NEMD) has become a catchall term to describe abnormal esophageal manometric findings that do not meet strict criteria for established esophageal motility disorders. The aim of this study was to determine whether NEMD is a real esophageal motility disorder characterized by impairment of its motor function or simply a manometric disturbance with no clinical consequences. METHODS: Esophageal transit of liquid and semisolids was studied using radioscintigraphic techniques in 10 symptomatic patients with manometrically diagnosed NEMD, 26 healthy control subjects, and 40 disease control subjects. The disease controls included 24 patients with achalasia, 9 with scleroderma, and 7 with diffuse esophageal spasm. RESULTS: Patients with NEMD had no impairment of liquid emptying compared with healthy controls. Liquid emptying was markedly delayed in patients with achalasia and scleroderma. However, semisolid emptying was markedly delayed in patients with NEMD compared with healthy controls (P < 0.001), and the extent of its delayed emptying was similar to that seen in patients with achalasia, scleroderma, and diffuse esophageal spasm. CONCLUSIONS: NEMD is not a manometric curiosity but a disorder characterized by selective impairment of semisolid emptying.

Adult↗

PubMed1993

Effect of menstrual cycle on esophageal emptying of liquid and solid boluses.

The effect of the menstrual cycle on esophageal emptying is unknown. We investigated the influence of the menstrual cycle on esophageal transit of liquid and solid boluses in 30 healthy, normally menstruating women who were 20 to 46 years of age. Each subject was studied during the follicular (days 8 through 10) and the luteal (days 18 through 20) phase of the menstrual cycle. Subjects swallowed a 10-ml bolus of water and two solid boluses, each radiolabeled with 100 microCi of 99mTc sulfur colloid. Esophageal scintigraphy was used to assess esophageal emptying of the liquid and solid boluses. Our results showed no significant differences in esophageal transit of either liquid or solid material between follicular and luteal phases. We conclude that esophageal emptying is unaffected by the phases of the menstrual cycle.

Adult↗

PubMed1993

Achalasia: prospective evaluation of relationship between lower esophageal sphincter pressure, esophageal transit, and esophageal diameter and symptoms in response to pneumatic dilation.

The aims of this study were to investigate a group of patients with achalasia prospectively to determine (1) the relationship between changes in symptoms and esophageal motor function in response to pneumatic dilation and (2) the effects of the balloon size as well as the frequency and duration of inflation on the outcome of treatment. Fourteen patients with achalasia who were symptomatic for a median duration of 27 months participated in the study. The patients were randomized to one combination of the following pneumatic dilation conditions: a 30- or 35-mm balloon dilator, one or two balloon inflations, and 20, 40, or 60 seconds per balloon inflation. A comprehensive assessment of their symptoms and esophageal motility, transit, and diameter were performed before and 3 months after pneumatic dilation. Pneumatic dilation provided significant relief of dysphagia (P < 0.01), but other symptoms (heartburn, regurgitation, and chest pain) remained unchanged. Pneumatic dilation also caused a significant decrease in lower esophageal sphincter pressure and esophageal diameter and improved esophageal emptying of a solid bolus. Nevertheless, no significant association was detected between changes in the symptom score for dysphagia and changes in objective response measures as a result of pneumatic dilation. Changes in the symptom score for dysphagia or objective responses were similar regardless of the size of the dilator used or the frequency and duration of the balloon inflations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Evaluation of 99Tcm nonspecific polyclonal IgG in the detection of rejection in a single lung transplant canine model.

Acute rejection is an important cause of graft failure in single lung transplantation, however, current noninvasive tests are neither sensitive nor specific for this diagnosis. The aim of this study was to determine whether 99Tcm-labelled human nonspecific polyclonal IgG (99Tcm-IgG) may serve as a marker for acute pulmonary rejection following allotransplantation in a dog model. Seventeen mongrel dogs were studied, including four controls and thirteen dogs which underwent surgery [right autotransplant recipient (n = 4), right unmodified allotransplant recipient (n = 5), and right immunosuppressed allotransplant recipient (n = 4)]. At 6 days following surgery, all dogs received 67Ga-citrate and 99Tcm-IgG. Two days later all dogs were sacrificed. Post-mortem examination revealed acute lung rejection in nine animals. No significant difference was found in the percentage uptake of both 99Tcm-IgG and 67Ga-citrate per gram of tissue between rejecting and nonrejecting transplanted lungs. In cases of moderate to severe rejection (n = 5), only 67Ga-citrate showed a significant difference (P = 0.03) in uptake between rejecting and contralateral native lungs, respectively. We conclude that 99Tcm-IgG does not accurately identify acute lung rejection in the early postoperative period.

Animals↗

PubMed1993

Evaluation of a radiolabeled somatostatin analog (I-123 octreotide) in the detection and localization of carcinoid and islet cell tumors.

The purpose of this study was to evaluate the usefulness of a radiolabeled analog of somatostatin (iodine-123 octreotide) in the detection and localization of known carcinoid and islet cell tumors and to correlate tumor uptake with the presence or absence of somatostatin receptors. I-123 octreotide studies were performed in 28 patients. Whole-body and tomographic studies were performed over a 2-day period after injection. Twenty-two of the 28 patients underwent tumor biopsy, and samples were analyzed for the presence of somatostatin receptors. Tumors were best seen on scans obtained 1-4 hours after injection. Of the 28 patients, 22 had positive scans with uptake in tumors, three showed photon-deficient uptake in regions of known tumor, and three had negative scans. Seventeen patients in whom results of tumor biopsy were positive for somatostatin receptors had positive scans, and one patient in whom results of biopsy were negative for somatostatin receptors had a negative scan. Previously unsuspected lesions were detected on the I-123 octreotide scans in four of the 28 patients. I-123 octreotide appears to be a useful tracer for the localization of neuroendocrine tumors and, most likely, other soft-tissue tumors as well.

Adenoma, Islet Cell↗