Search PubMed⌕ Search

Biomedical subjects

J R Mayo

Publications and source records attributed to J R Mayo.

At least 37 records · Page 2Linked to original sources
PubMed1995

Bronchial arterial response to contrast medium.

RATIONALE AND OBJECTIVES: Contrast agents have been shown to produce vasodilatory responses in several vascular beds. To our knowledge, however, their effect on the bronchial vasculature has not been examined. Clinically, contrast-induced bronchial vasodilation could potentially exacerbate life-threatening pulmonary hemorrhage during bronchial angiography for hemoptysis. In the current study, we systematically measured the bronchial vasodilatory response to diatrizoate meglumine 66% and diatrizoate sodium 10% (MD-76) and examined whether vasodilation would be mediated by nitric oxide (NO). METHODS: We measured bronchial blood flow in seven anesthetized, ventilated, open-chested sheep using an ultrasonic flow probe placed around the bronchial artery. Bronchial blood flow was recorded before and after injection of 2 ml MD-76 into the bronchial artery. The protocol was repeated after 20 min infusion of N omega-nitro-L-arginine (L-NA; 10(-2) mol/l), an NO-synthase inhibitor, into the bronchial artery. RESULTS: There was a 45 +/- 8 ml/min increase (p < .01) in bronchial blood flow after injection of MD-76, which was reduced to 20 +/- 6 ml/min (p < .01) after infusion of L-NA. CONCLUSION: Bronchial arterial injection of MD-76 results in a consistent increase in bronchial blood flow that is mediated partly by NO.

Animals↗
PubMed1995

Measurement of lung water content and pleural pressure gradient with magnetic resonance imaging.

The aim of this study was to develop a magnetic resonance (MR) sequence capable of measuring water content and the gravity-dependent gradient in lung density in normal lung. First, the MR signal from excised normal pig lung was characterized using a 2.1 T nuclear magnetic resonance (NMR) spectrometer. A multiecho sequence was then developed on a 0.15 T Picker MR scanner. This sequence was validated in excised normal pig lung by comparison with gravimetric lung water content. Finally, this sequence was used in five normal volunteers in the prone and supine positions during quiet breathing and in the supine position at total lung capacity (TLC). The ratio of lung water measured by MR and gravimetric techniques was 0.95 +/- 0.03. There was no significant difference in average lung density in the prone (0.21 +/- 0.03 g/ml) and in the supine (0.20 +/- 0.03 g/ml) positions. Lung density decreased at TLC (0.12 +/- 0.01 g/ml) (p < 0.01). Gradients in lung density were visible in all prone and supine scans at functional residual capacity (FRC), and on average the gradients were decreased by 90% at TLC. The average estimated pleural pressure gradient in the prone position was 0.13 +/- 0.08 cm H2O/cm lung and in the supine position was 0.38 +/- 0.23 cm H2O/cm lung. MRI allows measurement of lung water content and pleural pressure gradient.

Adult↗
PubMed1995

Diaphragmatic rupture: CT findings in 11 patients.

PURPOSE: To determine the signs of diaphragmatic rupture at computed tomography (CT) and the frequency of preoperative diagnosis with CT. MATERIALS AND METHODS: CT scans in 11 consecutive patients with surgically proved tears of the diaphragm due to blunt trauma were reviewed by two chest radiologists. The observers assessed the presence of discontinuity of the diaphragm, herniation of abdominal viscera or omentum, and waistlike constriction of the herniated stomach or bowel (collar sign). Hospital records were reviewed to confirm surgical findings and ascertain whether the diagnosis has been suggested at CT. RESULTS: In eight of 11 patients, rupture of the diaphragm was on the left, and in three it was on the right. In nine patients, diagnostic findings were identified retrospectively on CT scans; these included discontinuity of the diaphragm (n = 9), herniation of the abdominal organs or bowel (n = 7), and constriction of the stomach (n = 3). CONCLUSION: CT enables detection of most diaphragmatic tears due to blunt trauma.

Adult↗
PubMed1995

Measurement of lung expansion with computed tomography and comparison with quantitative histology.

The total and regional lung volumes were estimated from computed tomography (CT), and the pleural pressure gradient was determined by using the milliliters of gas per gram of tissue estimated from the X-ray attenuation values and the pressure-volume curve of the lung. The data show that CT accurately estimated the volume of the resected lobe but overestimated its weight by 24 +/- 19%. The volume of gas per gram of tissue was less in the gravity-dependent regions due to a pleural pressure gradient of 0.24 +/- 0.08 cmH2O/cm of descent in the thorax. The proportion of tissue to air obtained with CT was similar to that obtained by quantitative histology. We conclude that the CT scan can be used to estimate total and regional lung volumes and that measurements of the proportions of tissue and air within the thorax by CT can be used in conjunction with quantitative histology to evaluate lung structure.

Biopsy↗
PubMed1995

CT of the chest: minimal tube current required for good image quality with the least radiation dose.

OBJECTIVE: We wanted to determine minimal tube current (mAs) required for consistently good image quality on conventional 10-mm collimation chest CT and effect of tube current reduction on detection of mediastinal and lung abnormalities. Tube current reduction is desirable to reduce patient radiation dose. SUBJECTS AND METHODS: Prospectively, 30 consecutive patients (mean weight, 68 kg; range, 34-93 kg) older than 45 undergoing conventional chest CT with standard technique (120 kVp, 400 mAs) had four additional sections imaged at reduced tube current (200, 140, 80, 20 mAs) at two levels (tracheal carina and left atrium). CT scans were evaluated in random order by two independent observers who were blinded to technical factors used. Subjective image quality was graded on a five-point scale from non-diagnostic to excellent. Visualization of mediastinal adenopathy (n = 18), pleural plaques (n = 17), effusions (n = 28), lung parenchymal nodules (n = 37), and emphysema (n = 15) were assessed. The 400 mAs scan was considered the reference standard. RESULTS: When compared with the reference technique (400 mAs), the first and second (200 mAs and 140 mAs) reduction levels showed no significant difference (p > .05) in subjective image quality. A significant difference (p < .001) was seen at the third and fourth (80 mAs and 20 mAs) reduction levels. However, no significant difference (p > .05) was seen in detection of mediastinal or lung parenchymal abnormalities with different tube currents. CONCLUSION: A twofold reduction in tube current (400-140 mAs) and resultant radiation dose did not cause a significant change in subjective image quality or in detection of mediastinal or lung abnormalities with conventional chest CT. One hundred forty milliampere-seconds is the minimal tube current required to provide good image quality in patients of average weight.

Aged↗
PubMed1995

Perforated atherosclerotic ulcer of the aorta presenting with upper airway obstruction.

The authors describe an unusual presentation of penetrating atherosclerotic ulcer of the aorta in an 84-year-old man. The ulcer perforated the aorta, and hematoma extended into the soft tissues of the neck, causing upper airway and esophageal obstruction. The results of autopsy proved the findings of prior chest radiography and computed tomography.

Aged↗
PubMed1994

MR imaging of chest wall lesions.

To assess the magnetic resonance (MR) imaging findings of chest wall lesions, images from 45 patients were reviewed by two experienced chest radiologists. The study included 14 benign and 31 malignant lesions. Images were obtained on 1.5-T imagers with use of conventional T1-, proton-density, and T2-weighted sequences in transverse, coronal, and sagittal imaging planes. Where appropriate, motion artifact was minimized with respiratory compensation, spatial presaturation, flow compensation, and cardiac gating. Twelve of 14 benign lesions showed well-defined, smooth margins compared with 10 of 31 malignant lesions (P < .05). The remaining 21 malignant lesions had irregular or ill-defined margins and evidence of muscle, bone, or vascular invasion. A capsule or pedicle was seen only in benign lesions. Characteristic MR signal intensity was seen in all four lipomas and in the only arteriovenous malformation. The remaining benign and malignant lesions showed nonspecific signal intensity characteristics. MR imaging allows the detection of muscle, bone, or vascular invasion by chest wall tumors. However, as in other musculoskeletal regions, MR imaging does not allow confident distinction of benign from malignant chest wall lesions.

Adolescent↗
PubMed1994

Pulmonary parenchymal abnormalities of vascular origin: high-resolution CT findings.

High-resolution computed tomography (HRCT) is a proved imaging modality for use in assessment of infiltrative lung disease. Findings suggestive of infiltrative lung disease on HRCT scans include ground-glass attenuation, consolidation, nodules, and interlobular septal thickening. Similar patterns, however, may be caused by various vascular abnormalities including regional or diffuse increase in blood flow, pulmonary edema, pulmonary hypertension, and thromboembolism. A correct diagnosis can usually be made by careful analysis of the pulmonary vasculature. Parenchymal abnormalities of vascular origin are associated with increased or decreased vessel diameter, vascular compression, or intraluminal filling defect.

Humans↗
PubMed1994

Chronic infiltrative lung disease: comparison of diagnostic accuracies of radiography and low- and conventional-dose thin-section CT.

PURPOSE: To compare the accuracy of low-dose thin-section computed tomography (CT), chest radiography, and conventional-dose thin-section CT in diagnosis of chronic infiltrative lung disease (CILD). MATERIALS AND METHODS: Chest radiographs and low-dose (80-mAs) and conventional-dose (340-mAs) thin-section (1.5-mm) CT scans from 50 patients with CILD and 10 healthy control subjects were randomized and analyzed retrospectively. For CT, three images were obtained: at the aortic arch, at the tracheal carina, and 1 cm above the right hemidiaphragm. Two independent observers listed three likely diagnoses and recorded the degree of confidence in their first choice. RESULTS: A correct first-choice diagnosis was made more often with either CT technique than with radiography (P < .02). A high confidence level in the diagnosis was reached in 42% of radiographic, 61% of low-dose CT, and 63% of conventional-dose CT interpretations, which were correct in 92%, 90%, and 96% of the studies, respectively. CONCLUSION: The superior diagnostic accuracy of low-dose thin-section CT was achieved without an increase in effective radiation dose.

Adult↗
PubMed1994

Magnetic resonance imaging of the chest. Where we stand.

Although the improved soft tissue contrast, multiplanar capacity, intrinsic flow sensitivity, and lack of ionizing radiation make MR an ideal thoracic imaging modality, technical problems resulting from magnetic susceptibility effects and motion have significantly limited its application. Currently, with the exception of cardiovascular applications and assessment of Pancoast tumors, MR remains a secondary imaging modality to chest CT. Research into thoracic MR undoubtedly will expand the current clinical indications. Development of specialized pulse sequences to address the unique problems of MR in the thorax will improve image quality and expand its clinical role. Additionally, MR provides unique information not easily obtainable by other noninvasive imaging modalities, such as quantitative determination of lung water. Further research in this area may provide unique insights into the pathophysiology of chronic interstitial lung disease. As a result, the role of thoracic MR should change significantly by the turn of the century.

Contraindications↗
PubMed1993

T1 lung cancer: prevalence of mediastinal nodal metastases and diagnostic accuracy of CT.

To determine the prevalence of mediastinal lymph node metastases in T1 non-small cell lung cancer and assess the sensitivity and specificity of computed tomography (CT) in detection of such metastases, the CT scans and surgical findings in 104 patients with T1 lesions were reviewed. Nodes longer than 10 mm on the short or long axis were considered abnormal. All patients underwent thorough mediastinal lymph node dissection at mediastinoscopy or thoracotomy. A total of 362 lymph nodes were sampled. Nodal metastases were present in 22 patients (21%). The sensitivity of CT for metastases to individual nodal stations was 41% for nodes measured on the short axis and 55% for those measured on the long axis. The specificity was 93% and 86%, respectively. When the adjacent nodal stations were included in the analysis, the sensitivity of CT was 59% for nodes measured on the short axis and 77% for those measured on the long axis; the specificity was 91% and 73%, respectively. T1 lung cancer has a higher prevalence of lymph node metastasis than previously reported, and CT is recommended in the preoperative staging of this disease.

Adult↗
PubMed1993

High-resolution CT of the chest: radiation dose.

OBJECTIVE: The purpose of this study was to compare the skin radiation dose to the chest produced by high-resolution CT (HRCT) with the radiation dose produced by conventional CT. Previous studies have reported that radiation doses with HRCT are equal to or higher than those with conventional CT. These results, however, were based on the assumption that in HRCT, contiguous sections were scanned without the intersection gaps of 10 or 20 mm that are used clinically. SUBJECTS AND METHODS: We used radiotherapy verification film to measure the skin radiation dose in 56 patients who had chest CT scans. Twenty-two had 1.5-mm collimation HRCT scans at 10-mm intervals, 15 had 1.5-mm collimation HRCT scans at 20-mm intervals, and 19 had 10-mm collimation conventional CT scans at 10-mm intervals. Scan parameters were identical in all cases: 120 kVp, 200 mA, 2 sec. Step wedges were used to generate calibration films with identical beam quality on the CT scanner, and exposure was measured with an ionization chamber. Calibration films and patients' radiotherapy verification films were digitized, and the radiation dose was calculated. RESULTS: Mean skin radiation dose was 4.4 (standard error [SE], 0.2) mGy for 1.5-mm HRCT scans at 10-mm intervals, 2.1 (SE, 0.1) mGy at 20-mm intervals, and 36.3 (SE, 0.9) mGy for conventional 10-mm scans at 10-mm intervals. CONCLUSION: HRCT scanning at 10- and 20-mm intervals produced 12% and 6%, respectively, of the radiation dose associated with conventional CT. This is considerably less radiation than suggested in earlier studies. Combining HRCT scans at 20-mm intervals with low-dose scan (20 mA, 2-sec scans) would result in an average skin dose comparable with the dose administered with chest radiography.

Adult↗
PubMed1993

Thoracic magnetic resonance imaging: physics and pulse sequences.

The article summarizes the basic concepts of magnetic resonance (MR) physics so that radiologists can optimize the images obtained in MR imaging of the chest. The specification of thoracic MR scan protocols is more complex than for other body regions because of cardiac and respiratory motion and blood flow. Various motion suppressing techniques such as motion compensation, respiratory compensation, and spatial presaturation have been developed, but their appropriate application is facilitated by a thorough understanding of the imaging process. Magnetic susceptibility and low proton density limit the usefulness of MR imaging in the assessment of the lung parenchyma. Nevertheless, recent studies have shown considerable improvement in image quality with the use of short echo times. Suggested imaging protocols for the evaluation of chest wall, mediastinum, hilum, heart, and great vessels are discussed.

Humans↗
PubMed1992

High-resolution computed tomography of experimental hydrostatic pulmonary edema.

To better understand the distribution and clearance mechanisms of extravascular lung water (EVLW) in pulmonary edema, computed tomographic (CT) scans of isolated canine lungs were obtained. In this model, there is no active lymphatic drainage. Fourteen isolated lobes were inflated with oxygen, and edema was induced by infusion of normal saline solution. Two volumes of saline were used, 50 percent and 150 percent of initial wet lobar weight. Six 10-mm- and 1.5-mm-collimation CT scans were obtained at 10-mm intervals from the hilum to the periphery of the lobe before and after each of the two stages of pulmonary edema. The CT scans were reviewed independently by two chest radiologists and were assessed by CT densitometry. Both subjective analysis and CT densitometry showed a predominantly central peribronchial distribution of EVLW in the isolated lungs. Airway wall thickness also increased from the control value (average thickness, 1.0 mm) to 150 percent edema (average thickness, 1.5 mm) (p less than 0.001). We postulate that the peribronchial distribution of fluid is due to a pressure gradient from the alveolar interstitium to the interstitium around the blood vessels and airways at the hilum. This gradient may play a major role in the characteristic perihilar and peribronchial distribution of EVLW seen radiologically in patients with hydrostatic pulmonary edema.

Animals↗
PubMed1992

Tuberculosis of the thymus.

Tuberculosis is increasing in prevalence in North America, mainly due to HIV infection. We describe an unusual case of TB of the thymus in a HIV sero-negative Filipino immigrant who preoperatively was thought to have a thymoma. We describe the clinical, radiologic and pathologic findings and review the literature on TB of the thymus.

Adult↗
PubMed1992

Value of MR imaging in the evaluation of chronic infiltrative lung diseases: comparison with CT.

The value of MR imaging was compared with that of high-resolution CT in assessing chronic infiltrative lung disease in 25 patients. The cases included nine patients with usual interstitial pneumonia, six with sarcoidosis, four with hypersensitivity pneumonitis, and six with miscellaneous conditions. The diagnosis was proved by biopsy (n = 17) or by means of clinical, laboratory, and radiologic criteria (n = 8). All patients had 1.5-T MR imaging and CT of the chest. Cardiac-gated T1-, proton density-, and T2-weighted spin-echo sequences were obtained. Initially, the MR images were assessed independently; later they were compared directly with the corresponding CT scans. In six patients, MR images and CT scans were obtained before open lung biopsy, and the images and scans were assessed prospectively. CT was superior to MR imaging in the anatomic assessment of the lung parenchyma and in showing fibrosis. However, areas of air-space opacification (ground-glass opacities) were seen as well on MR as on high-resolution CT. In the six patients who had open lung biopsy, areas of air-space opacification seen on MR and on CT corresponded to areas of active alveolitis or air-space infiltrates pathologically. Follow-up in six patients showed equal degrees of change in the air-space opacification over time on MR and CT. We conclude that, although MR imaging is inferior to high-resolution CT in the assessment of chronic infiltrative lung diseases, it may play a role in the assessment and follow-up of patients with air-space opacification.

Adult↗
PubMed1992

MR imaging of the lungs: value of short TE spin-echo pulse sequences.

OBJECTIVE: An experimental short echo delay (TE = 7 msec) T1-weighted spin-echo sequence was compared with a conventional (TE = 20 msec) T1-weighted spin-echo sequence in the assessment of normal and abnormal lung parenchyma. Comparison was also made with high-resolution CT of abnormal lung parenchyma. SUBJECTS AND METHOD: At 1.5 T, an experimental short echo delay T1-weighted multislice spin-echo sequence (TR = RR interval, TE = 7 msec) was compared with an optimal conventional T1-weighted spin-echo sequence (TR = RR interval, TE = 20 msec, spatial presaturation). Ten healthy volunteers were examined with both sequences. The mean signal intensity and signal-to-noise ratios were calculated in lung parenchyma for both sequences. Two radiologists compared the visualization of normal lung parenchymal structures with the two techniques. In 24 patients with diffuse lung disease, results with both MR sequences and with high-resolution CT were compared. RESULTS: The signal intensity was significantly greater (p < .001) with the TE of 7 msec than with the TE of 20 msec, resulting in a 3.5-fold improvement in the signal-to-noise ratio. The 7-msec TE improved visualization of lung parenchymal structures, including peripheral vessels, interlobular septa or veins, and centrilobular arteries. In the patients with diffuse lung disease, pulmonary parenchymal abnormalities were better visualized on the images with TEs of 7 msec than on images with TEs of 20 msec. When compared with high-resolution CT, the sequence with a TE of 7 msec provided comparable assessment of air-space opacification and dense consolidation, but it was inferior to high-resolution CT in the anatomic assessment of lung parenchyma. CONCLUSION: This experimental spin-echo sequence with a TE of 7 msec significantly improves the signal-to-noise ratio, allowing improved visualization of normal and abnormal pulmonary parenchyma when compared with conventional spin-echo images with a TE of 20 msec. Although anatomic detail remains inferior to that seen with high-resolution CT, the improved image quality with a TE of 7 msec suggests that assessment and follow-up of parenchymal lung disease might be possible with MR, thereby avoiding ionizing radiation.

Adult↗