Pulmonary MR angiography with contrast agent at 4 Tesla: a preliminary result

In this study, pulmonary MR angiography (MRA) using a tailored coil at 4 Tesla in conjunction with an intravenous injection of contrast agent is described. Three-dimensional gradient-echo images were obtained during the intravenous injection of 0.05, 0.1, and 0.2 mmol/kg body weight of gadodiamide to investigate the signal enhancement effect of the contrast agent in pulmonary arteries qualitatively and quantitatively. In the qualitative analysis, the subsegmental branches were visualized on every dose. In the quantitative analysis, the average contrast-to-noise ratios (CNRs) of the main pulmonary arteries increased in a dose-dependent manner. However, the CNRs of segmental arteries did not increase as the dose of contrast agent increased, as observed at 1.5 Tesla MRI. These observations demonstrate the feasibility of delineating the pulmonary vasculature using a contrast agent; however, our results also suggest possible high-field-related disabilities that need to be overcome before high-field (> or =4 Tesla) MRI can be used to full advantage.

Reliability of soft-copy versus hard-copy interpretation of emergency department radiographs: a prototype study

OBJECTIVE

The purpose of this study was to compare the diagnostic reliability of hard-copy and soft-copy interpretation of radiographs obtained in the emergency department using a methodology for evaluating imaging systems when independent proof of the diagnosis is not available.

MATERIALS AND METHODS

We collected radiographs from a stratified sample of 100 patients seen in the emergency department. The images were obtained using computed radiography, and the digital images were printed on film and stored for display on a workstation. A group of seven experienced radiologists reported the cases using both film and the workstation display. The results were analyzed using mixture distribution analysis (MDA).

RESULTS

The reliability expressed as the percentage of agreement of a typical observer relative to the majority was computed from the MDA. The result was 90% for both hard copy and soft copy with bootstrap confidence intervals of 86-94%.

CONCLUSION

We conclude that, in the emergency department, soft-copy interpretation is as reliable as hard-copy interpretation. The strength of this conclusion depends on the validity of the MDA approach as well as the extent to which the observer sample and case sample are representative of the emergency department.

Dynamic observation of pulmonary perfusion using continuous arterial spin-labeling in a pig model

The continuous arterial spin-labeling (CASL) method of perfusion MRI is used to observe pulmonary perfusion dynamically in an animal model. Specifically, a respiratory-triggered implementation of the CASL method is used with approximate spatial resolution of 0.9 x 1.8 x 5.0 mm (0.008 cc) and 2-minute temporal resolution. Perfusion MRI is performed dynamically during repeated balloon occlusion of a segmental pulmonary artery, as well as during pharmacological stimulation. A total of three Yorkshire pigs were studied. The results demonstrate the ability of the endogenous spin-labeling method to characterize the dynamic changes in pulmonary perfusion that occur during important physiological alterations.

Electron beam computed tomography for the quantification of aortic valvular calcification

BACKGROUND AND AIM OF THE STUDY

Calcific aortic stenosis is common in the elderly; indeed, 30-60% of patients with mild 'senile' aortic stenosis will progress to severe obstruction. Nonetheless, predictors of progression are incompletely defined, and non-invasive technologies capable of quantifying aortic valve calcium are needed. The reliability of electron beam computed tomography (EBCT) was evaluated for quantification of aortic valve calcium content.

METHODS

Nineteen patients with and without restrictive valve calcification underwent EBCT scanning. Separate calcium scores, 30 s apart, were obtained in all patients, and the Spearman correlation coefficient was calculated between measurements. The relationship between dichotomized mean calcium score and aortic valve area was also investigated.

RESULTS

There was excellent correlation between calcium scores (R = 0.99, p = 0.0001), as well as a significant inverse relationship between calcium scores in the upper and lower ranges and aortic valve area (p = 0.002).

CONCLUSION

EBCT can be used for reproducible quantitation of aortic valve calcification. While at their extremes, calcium scores are inversely related to aortic valve area, further evaluation is needed to define the precise nature of this relationship throughout the spectrum of stenosis severity. EBCT holds promise in the longitudinal assessment of valvular calcification progression and its response to potential medical therapies.

Utility of high resolution computed tomography in predicting bronchiolitis obliterans syndrome following lung transplantation: preliminary findings

This study was undertaken to evaluate the efficacy of high resolution computed tomography (HRCT) in predicting the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients. Fifty lung transplant patients who were clinically stable and without evidence of BOS were evaluated for the presence of four HRCT features reported to be associated with bronchiolitis obliterans: mosaic attenuation on inspiratory CT (mosaic perfusion), mosaic attenuation on expiratory CT (air trapping), bronchiectasis, and tree-in-bud opacities. CT exams were part of an annual surveillance process with the hope of predicting subsequent development of BOS. Diagnosis of BOS was made in 9 of 50 patients as indicated by a fall in FEV1 of greater than 20% of a stable baseline. None of the radiographic features associated with clinically established BOS were both sensitive and specific in the prediction of BOS. Air trapping demonstrated moderate sensitivity (56%, 5/9) and moderate specificity (76%, 35/46) for prediction of BOS in the year following the CT exam. Bronchiectasis, the most reliable indicator of the presence of BOS was a poor predictor of subsequent BOS with an 11% (1/9) sensitivity but had high specificity (96%, 44/46). No high resolution CT features accurately predicted the development of BOS.

Pulmonary arteriovenous malformations: three-dimensional gadolinium-enhanced MR angiography-initial experience

PURPOSE

To determine whether three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography could be used to identify pulmonary arteriovenous malformations (PAVMs) and to accurately identify the size and number of feeding arteries.

MATERIALS AND METHODS

Eight patients suspected of having PAVM were examined with three-dimensional MR angiography at 1.5 T. Images were reviewed by a single radiologist blinded to conventional angiographic findings who evaluated each image for the size, number, and location of PAVMs, as well as for the size and number of feeding arteries. Five patients underwent conventional angiography with embolization therapy, and one patient underwent lobectomy. Two patients did not undergo either surgery or angiography.

RESULTS

Three-dimensional MR angiography revealed nine (90%) of 10 PAVMs that were confirmed at conventional angiography (n = 9) or examination of a surgical specimen (n = 1). The single PAVM that was not identified prospectively at MR angiography was small (3-4 mm) and peripheral. Two additional PAVMs were identified in the two patients who did not undergo surgery or angiography.

CONCLUSION

Three-dimensional MR angiography is a promising technique for use in the diagnosis of PAVM, although small (<5-mm) PAVMs may be more difficult to identify with the technique. The technique is a particularly useful means of noninvasively demonstrating the size and number of feeding arteries prior to treatment.

Distribution of thrombi in acute lower extremity deep venous thrombosis: implications for sonography and CT and MR venography

OBJECTIVE

Our objective was to determine the typical distribution of thrombi in acute lower extremity deep venous thrombosis as a means of evaluating the validity of imaging techniques that only include the common femoral and popliteal veins, but not the superficial femoral vein.

MATERIALS AND METHODS

The results of 2704 lower extremity venous sonograms, obtained in 2026 consecutive patients over a 4-year interval, were reviewed retrospectively. The distribution of acute deep venous thromboses across various lower extremity venous segments was analyzed for this population, which consisted of both symptomatic and asymptomatic patients.

RESULTS

Of 2704 lower extremities studied with duplex sonography, acute deep venous thrombosis was identified in 269 (9.9%). Of these 269 cases, acute deep venous thrombosis was isolated to the superficial femoral vein in 60 (22.3%). The remaining 209 cases (77.7%) showed thrombus that extended into the common femoral or popliteal veins (or both).

CONCLUSION

An abbreviated imaging study that evaluates only the common femoral and popliteal veins would fail to identify more than 20% of lower extremity acute deep venous thromboses in a population like ours. Although evaluation of the superficial femoral vein requires additional time and resources, evaluation of this segment may prevent a substantial number of thrombi from being missed.

Accuracy of CT angiography versus pulmonary angiography in the diagnosis of acute pulmonary embolism: evaluation of the literature with summary ROC curve analysis

RATIONALE AND OBJECTIVES

The authors performed this study to estimate, by using published data, the sensitivity and specificity of computed tomographic (CT) angiography in the evaluation of suspected acute pulmonary embolism (PE).

MATERIALS AND METHODS

Summary receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity and specificity of CT angiography in the diagnosis of acute PE. Pulmonary angiography was used as the diagnostic standard of reference. The authors reviewed the results of 11 independent studies published in the English-language literature between January 1992 and June 1999.

RESULTS

The sensitivity of CT angiography in the diagnosis or exclusion of PE in the central pulmonary arteries (to the level of the segmental pulmonary arteries) ranged from 0.74 to 0.81 on the basis of specificities of 0.89-0.91. The sensitivity of CT angiography in the diagnosis or exclusion of PE in all pulmonary arteries (to the level of the subsegmental pulmonary arteries) was 0.68 on the basis of a specificity of 0.91.

CONCLUSION

On the basis of the studies in the current literature, most of which used 5.0-mm collimation and single-detector CT, CT angiography may be less accurate in the diagnosis of PE than previously reported. With improvements in data acquisition, particularly the use of thinner section collimation and multidetector CT, and in the increased use of workstations for data analysis, the accuracy and utility of CT angiography will require continued investigation.

Detection and localization of pulmonary air leaks using laser-polarized (3)He MRI

Pulmonary air leaks were created in the lungs of Yorkshire pigs. Dynamic, 3D MRI of laser-polarized (3)He gas was then performed using a gradient-echo pulse sequence. Coronal magnitude images of the helium distribution were acquired during gas inhalation with a voxel resolution of approximately 1.2 x 2.5 x 8 mm, and a time resolution of 5 sec. In each animal, the ventilation images reveal focal high-signal intensity within the pleural cavity at the site of the air leaks. In addition, a wedge-shaped region of increased parenchymal signal intensity was observed adjacent to the site of the air leak in one animal. (3)He MRI may prove helpful in the management of patients with pulmonary air leaks.

The costs of CT procedures in an academic radiology department determined by an activity-based costing (ABC) method

PURPOSE

The purpose of this work was to determine the costs of computed tomography (CT) procedures in a large academic radiology department, including both professional (PC) and technical (TC) components, by analyzing actual resource consumption using an activity-based costing (ABC) method and comparing them with Medicare payments.

METHOD

Over a 12 month period from July 1, 1996, to June 30, 1997, 1,011 CT procedures, representing 16 Physicians' Current Procedural Terminology (CPT) codes and 98.3% of CT studies performed, were carefully observed by a research assistant trained in ABC methodology. Information collected during these time and motion studies included personnel/machine time and direct materials used. Actual resource units used during the different activities in each CT procedure were valued using appropriate cost drivers. Unit values for both direct and overhead costs were calculated: the cost of an individual procedure equaled the sum of component costs. Costs were compared with PC and TC payments according to the 1997 Medicare Fee Schedule.

RESULTS

Total costs of CPT codes 70450 (CT Head unenhanced), 71260 (CT Chest enhanced), and 74160 (CT Abdomen enhanced), which represented 71.2% of CT studies performed, were $189.19, $273.53, and $343.20, respectively. For all 16 nonmodified CPT codes analyzed, Medicare's professional reimbursement was less than the professional cost, whereas its technical reimbursement exceeded respective cost in 14 of the 16 codes.

CONCLUSION

In the setting and time period studied, Medicare underreimbursed professional costs while overreimbursing technical costs.

Recent advances in pulmonary imaging

Recent years have witnessed an explosion in imaging technology applicable to chest medicine. These include CT and magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism, and high-resolution CT for the detection and characterization of diffuse lung diseases and the quantification of emphysema. Newly developed approaches to pulmonary functional imaging using CT and MRI have been applied to the evaluation of pulmonary ventilation and perfusion and to the detection of small airways disease. Volumetric CT imaging techniques together with advanced image processing have made possible "virtual bronchoscopy." Positron emission tomography provides an important new approach to the accurate detection and staging of chest malignancies and to the evaluation of pulmonary nodules. Finally, new digital imaging techniques, which are rapidly replacing conventional x-ray film, offer the possibility of computer-aided diagnosis.

Pulmonary perfusion: respiratory-triggered three-dimensional MR imaging with arterial spin tagging--preliminary results in healthy volunteers

The authors used a spin-tagging method of magnetic resonance perfusion imaging to measure pulmonary perfusion in eight healthy volunteers with use of a respiratory-triggered three-dimensional pulse sequence. The average signal intensity (SI) decrease upon arterial labeling was 24%. The perfusion SI increased by 21% after exercise (P = .02). Focal blood flow abnormalities were observed in a patient with chronic obstructive pulmonary disease.

Spontaneous tension pneumopericardium complicating staphylococcal pneumonia

The authors describe a patient with spontaneous pneumopericardium complicating staphylococcal pneumonia and empyema that resulted in cardiac tamponade. Spontaneous pneumopericardium is an unusual disorder. The causes and clinical findings of pneumopericardium are reviewed, as are the radiographic features that differentiate this condition from pneumomediastinum. Early recognition of pneumopericardium is important, because emergent pericardiocentesis may be required if there is clinical evidence of tamponade.

Advanced emphysema: preoperative chest radiographic findings as predictors of outcome following lung volume reduction surgery

PURPOSE

To determine whether preoperative chest radiographic findings alone can reliably predict which patients will achieve the best functional outcome of lung volume reduction surgery.

MATERIALS AND METHODS

The preoperative chest radiographs obtained in 57 patients who had undergone lung volume reduction surgery were retrospectively scored by five blinded readers for severity and distribution of emphysema, evidence of lung compression, disease heterogeneity, and other features. Comparisons were made with the 3-6-month postoperative functional outcome for each patient.

RESULTS

High disease heterogeneity (score > 2) and unequivocal lung compression (score 1) both were 100% predictive of a favorable outcome (FEV1 increase, > or = 30%). Low heterogeneity (score < 1) was 94% predictive of an unfavorable outcome (FEV1 increase < 30%), as was a lack of lung compression, which was 92% predictive of an unfavorable outcome. These two features also correlated with an improved 6-minute walk test result, although this correlation was weaker.

CONCLUSION

Chest radiography alone may be sufficient for initial screening. High disease heterogeneity and lung compression on chest radiographs are highly predictive of a favorable functional outcome.

T2* and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging

OBJECTIVE

To obtain T2* and proton density measurements of normal human lung parenchyma in vivo using submillisecond echo time (TE) gradient echo (GRE) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Six normal volunteers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-holding with acquisition times of 7-16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding measurements of T2* and proton density relative to chest wall muscle. Measurements in supine and prone position were compared, and effects of the level of lung inflation on lung signal were also evaluated.

RESULTS

The signal from the lung parenchyma diminished exponentially with prolongation of TE. The measured T2* in six normal volunteers ranged from 0.89 to 2.18 ms (1.43 +/- 0.41 ms, mean +/- S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29 +/- 0.08, mean +/- S.D.). Calculated T2* values of 1.46 +/- 0.50, 1.01 +/- 0.29 and 1.52 +/- 0.18 ms, and calculated relative proton densities of 0.20 +/- 0.03, 0.32 +/- 0.13 and 0.35 +/- 0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior-posterior proton density gradient was reversed in the prone position. There was a pronounced increase in signal from lung parenchyma at maximum expiration compared with maximum inspiration. The ultrashort TE GRE technique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise.

CONCLUSION

Quantitative in vivo measurements of lung T2* and relative proton density in conjunction with high-signal parenchymal images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence.

Fast magnetic resonance imaging of the lung

The impact of fast MR techniques developed for MR imaging of the lung will soon be recognized as equivalent to the high-resolution technique in chest CT imaging. In this article, the difficulties in MR imaging posed by lung morphology and its physiological motion are briefly introduced. Then, fast MR imaging techniques to overcome the problems of lung imaging and recent applications of the fast MR techniques including pulmonary perfusion and ventilation imaging are discussed. Fast MR imaging opens a new exciting window to multi-functional MR imaging of the lung. We believe that fast MR functional imaging will play an important role in the assessment of pulmonary function and disease process.

MRI study of regional variations of pharyngeal wall compliance in cats

Upper airway compliance indicates the potential of the airway to collapse and is relevant to the pathogenesis of obstructive sleep apnea. We hypothesized that compliance would vary over the rostral-to-caudal extent of the pharyngeal airway. In a paralyzed isolated upper airway preparation in cats, we controlled static upper airway pressure during magnetic resonance imaging (MRI, 0.391-mm resolution). We measured cross-sectional area and anteroposterior and lateral dimensions from three-dimensional reconstructed MRIs in axial slices orthogonal to the airway centerline. High-retropalatal (HRP), midretropalatal (MRP), and hypopharyngeal (HYP) regions were defined. Regional compliance was significantly increased from rostral to caudal regions as follows: HRP < MRP < HYP (P < 0.0001), and compliance differences among regions were directly related to collapsibility. Thus our findings in the isolated upper airway of the cat support the hypothesis that regional differences in pharyngeal compliance exist and suggest that baseline regional variations in compliance and collapsibility may be an important factor in the pathogenesis and treatment of obstructive sleep apnea.

State-related changes in upper airway caliber and surrounding soft-tissue structures in normal subjects

State-dependent changes in upper airway caliber were studied with magnetic resonance imaging (MRI) techniques. We hypothesized that changes in airway caliber during sleep in normal subjects would result from positional and dimensional changes in upper airway soft-tissue structures, including the lateral pharyngeal walls, tongue, and soft palate. We used MRI to study 15 normal subjects during wakefulness and sleep. Sleep was facilitated by one night of sleep deprivation prior to MRI. During sleep, the volume of the retropalatal (RP) airway was reduced by 19% (p = 0.03). The volume of the retroglossal (RG) airway was not significantly reduced during sleep, suggesting that the RP region may be more likely to collapse. The mean minimal cross-sectional airway area was reduced by 228% (p = 0.004) in the RP and by 22% (p = 0.02) in the RG region during sleep as compared with values in anatomically matched axial images during wakefulness. Airway anteroposterior (AP) and lateral dimensions were also significantly reduced in the RP region. Airway narrowing in the RP region was associated with a 7% increase in thickness of the lateral pharyngeal walls (p = 0.04). In nine subjects, sagittal data showed significant posterior displacement of the soft palate during sleep as compared with wakefulness. Multiple linear regression analyses indicated that reduction in the RP airway area during sleep resulted from posterior movement of the soft palate, thickening of the lateral pharyngeal walls, and an increase in tongue oblique distance. We conclude that the lateral pharyngeal walls play an important role in upper airway narrowing during sleep in normal subjects.

Upper airway and soft tissue structural changes induced by CPAP in normal subjects

Nasal continuous positive airway pressure (CPAP) is the treatment of choice for adults with obstructive sleep apnea. CPAP is known to increase upper airway size; however, the direct effects of CPAP on soft tissue structures surrounding the upper airway are less well understood. Magnetic resonance imaging was used to study the effect of incremental levels (0, 5, 10, and 15 cm H2O) of CPAP on the upper airway and surrounding soft tissue structures in 10 normal subjects. Progressive increases in CPAP resulted in the following major findings: (1) airway volume and airway area (measured at several different locations [midregion, minimal, maximal]) within the retropalatal and retroglossal regions increased; (2) lateral airway dimensional changes were greater than anterior-posterior changes; (3) lateral upper airway soft tissue structural changes were significantly greater than anterior-posterior changes; (4) lateral pharyngeal wall thickness decreased and the distance between the lateral parapharyngeal fat pads increased. An inverse relationship was demonstrated between CPAP level and pharyngeal wall thickness; (5) minimal changes were noted in the soft palate and tongue. These data suggest that the lateral pharyngeal walls are more "compliant" than the soft palate and tongue. This investigation provides further evidence that the lateral pharyngeal walls play an important role in mediating upper airway caliber.

Pulmonary MR angiography

Recent technical improvements have made pulmonary MR angiography (MRA) feasible. The technique is attractive because it is noninvasive, provides a full three-dimensional (3D) display of the pulmonary vasculature, and potentially can be combined with MR venography of the lower extremities and pelvis for the comprehensive diagnosis of thromboembolism. Approaches to acquiring pulmonary MR angiograms are currently being developed and include both two-dimensional and 3D time-of-flight methods, breath-hold and non-breath-hold techniques, and the use of gadolinium-based contrast enhancement. The results of initial studies using pulmonary MRA for the detection of pulmonary embolism are encouraging, but they must be evaluated in conjunction with newly developed fast CT scanning techniques. This article reviews the state of development of pulmonary MRA, the current clinical applications of the technique, and the prospects for future development.

Preoperative MR imaging in hyperparathyroidism: results and factors affecting parathyroid detection

OBJECTIVE

To determine the sensitivity of MR imaging for the detection of abnormal parathyroid glands in patients with biochemical evidence of hyperparathyroidism and to identify the factors affecting detection.

SUBJECTS AND METHODS

Between 1985, 82 patients with biochemical proof of hyperparathyroidism were referred for MR imaging of the parathyroid glands prior to surgery. Axial T1- (600/20 [TR/TE]) and T2-weighted (2500/40, 80) spin-echo images were obtained using an anterior neck surface coil. The interpretation of the MR image was compared with the findings at surgery and also correlated with gland histology, volume, and weight. Cases in which a false-positive or false-negative diagnosis was made were reviewed to determine the factors affecting detection.

RESULTS

MR imaging detected 71 of 92 (77%) surgically proven abnormal glands (sensitivity, 77%; 95% confidence interval (CI), 68-86%) and misdiagnosed five (1.6%) of 314 normal glands as abnormal. There was no difference in the detection of enlarged glands in patients presenting for the first time (n = 71) (sensitivity, 77%; 95% CI, 66-86%) compared with patients with recurrent hyperparathyroidism (n = 12) (sensitivity, 77%; 95% CI, 46-95%). There was no significant difference in the detection of adenomas (sensitivity, 77%; 95% CI, 65-86%) compared with hyperplasia (sensitivity, 71%; 95% CI, 42-92%). Of five patients with ectopic parathyroid glands (1.6%), four had had previous surgery. All five glands were successfully located (three mediastinal, two in the neck). Factors contributing to a false-negative MR imaging diagnosis included small gland size and thyroid disease. Four of five false-positive diagnoses were due to enlarged lymph nodes being mistaken for parathyroid glands.

CONCLUSIONS

MR imaging is an accurate technique for investigation of hyperparathyroidism. Pitfalls include low sensitivity for the identification of small glands, misinterpretation of enlarged lymph nodes as parathyroid adenomas, and misinterpretation because of thyroid disease. MR imaging is particularly useful in the investigation of patients who remain hypercalcemic following initial surgery.

Pulmonary thromboembolism: recent developments in diagnosis with CT and MR imaging

Recent technical advances in computed tomography (CT; helical and electron beam) and magnetic resonance (MR) imaging have spurred a renewed interest in these modalities for the diagnosis of acute and chronic pulmonary embolism (PE). These techniques can enable accurate clot detection down to segmental pulmonary arteries, with CT currently allowing more accuracy than that with MR imaging. Ongoing technical advances, particularly in MR angiography, will likely increase diagnostic accuracy. Inability to reliably detect subsegmental acute emboli may not prove to be a clinically significant limitation if lung imaging is coupled with evaluation for deep venous thrombosis. MR imaging can potentially accomplish this within a single examination. Incorporation of CT and MR imaging into diagnostic algorithms for suspected PE can be cost-effective. Evaluation of these new modalities should be based on patient outcome, not solely on clot detectability. Well-designed clinical trials are warranted before CT and MR imaging can be used routinely in the diagnosis of acute PE.

Upper airway and soft tissue anatomy in normal subjects and patients with sleep-disordered breathing. Significance of the lateral pharyngeal walls

The geometry and caliber of the upper airway in apneic patients differs from those in normal subjects. The apneic airway is smaller and is narrowed laterally. Examination of the soft tissue structures surrounding the upper airway can lead to an understanding of these apneic airway dimensional changes. Magnetic resonance imaging was utilized to study the upper airway and surrounding soft tissue structures in 21 normal subjects, 21 snorer/mild apneic subjects, and 26 patients with obstructive sleep apnea. The major findings of this investigation in the 68 subjects were as follows: (1) minimum airway area was significantly smaller in apneic compared with normal subjects and occurred in the retropalatal region; (2) airway narrowing in apneic patients was predominantly in the lateral dimension; there was no significant difference in the anterior-posterior (AP) airway dimension between subject groups; and (3) distance between the rami of the mandible was equal between subject groups, and thus the narrowing of the lateral dimension was not explained by differences in bony structure; (4) lateral airway narrowing was explained predominantly by larger pharyngeal walls in apneic patients (the parapharyngeal fat pads were not closer together as one would expect if the airway walls were compressed by fat); and (5) fat pad size at the level of the minimum airway was not greater in apneic than normal subjects. At the minimum airway area, thickness of the lateral pharyngeal muscular walls rather than enlargement of the parapharyngeal fat pads was the predominant anatomic factor causing airway narrowing in apneic subjects.

MR imaging with spatial modulation of magnetization in the evaluation of chronic central pulmonary thromboemboli

PURPOSE

To assess the diagnostic value of magnetic resonance (MR) imaging with SPAMM (spatial modulation of magnetization) in the identification of chronic central pulmonary thromboemboli.

MATERIALS AND METHODS

Twelve patients with pulmonary hypertension and five healthy volunteers were prospectively studied with a 1.5-T MR imaging system. The SPAMM technique was integrated into a conventional cardiac-synchronized spin-echo (SE) sequence. Six of the 12 patients had central thromboemboli.

RESULTS

In the healthy subjects, intravascular stripes in the central pulmonary arteries disappeared as a result of flow within 100 msec after the R wave. Areas of persistent stripes were identified in seven of eight central pulmonary arteries with thromboemboli. Conversely, in the 16 central pulmonary arteries without clot, intraluminal stripes disappeared despite the presence of flow-related signal (sensitivity = 88%, specificity = 100%, accuracy = 96%).

CONCLUSION

SPAMM appears to be a simple and effective technique for differentiating central pulmonary arterial thromboemboli from flow-related signal frequently observed with pulmonary hypertension.

Pulmonary aspergillosis in patients with AIDS. Clinical and radiographic correlations

OBJECTIVE

To evaluate the clinical and radiographic features of pulmonary aspergillosis as they present in AIDS patients; in particular, to determine similarities and differences between Aspergillus infection in patients with AIDS vs those without AIDS.

SUBJECTS AND METHODS

Six new cases of confirmed or probable pulmonary aspergillosis were discovered during a search of hospital records. These are reviewed with 30 previously reported cases with special attention to radiographic appearance of disease and how radiographic appearance influences clinical outcome.

RESULTS

Symptoms of pulmonary aspergillosis in AIDS were nonspecific, most often including fever, cough, and dyspnea, and less commonly, chest pain or hemoptysis. Major risk factors for the development of pulmonary aspergillosis in patients with AIDS were steroid administration and neutropenia. Neutropenia was often a complication of therapies for AIDS, in particular, ganciclovir and zidovudine. Radiographic appearance of disease could be divided into three general categories. One third of the patients (13/36) presented with cavitary upper lobe disease resembling noninvasive or chronic necrotizing aspergillosis. Fatal hemoptysis occurred in 42 percent of patients with this form of disease. Twenty-two percent (8/36) of the cases presented as a nondescript focal alveolar opacity similar to invasive aspergillosis. In several patients, the focal infiltrate remained stable for several months, a feature that is unusual for aspergillosis in non-AIDS patients. The air crescent sign was present in none of the 36 reported cases. Patients with only focal disease had the best prognosis of patients with pulmonary aspergillosis. Bilateral alveolar or interstitial disease similar to invasive aspergillosis was present in 23 percent (9/36) of the patients. Bilateral disease appears to be a marker for disseminated infection and was associated with a high mortality due to aspergillosis. Two new forms of bronchial aspergillosis (5/36 cases) have been described previously. These patients presented with either obstructing fungal casts or bronchial pseudomembranes demonstrated bronchoscopically. In some patients with the bronchial forms of aspergillosis, transient alveolar opacities were seen on chest radiographs. These opacities may represent regions of atelectasis due to airway obstruction. One patient who had bilateral pneumothoraces without parenchymal opacities did not correspond to any of the three previously mentioned categories. Mortality due to aspergillosis was greater than 50 percent among AIDS patients. Death was subsequent to fatal hemoptysis or widespread pulmonary or systemic infection.

CONCLUSION

Unlike other risk groups that tend to contract only one form of pulmonary aspergillosis, AIDS patients can develop the whole spectrum of aspergillosis-related pulmonary disorders, including chronic cavitary, invasive, and bronchial forms of aspergillosis. Clinical symptoms are nonspecific and major risk factors include neutropenia, which is often a side effect of various therapies for AIDS, and steroid administration. Patients with the chronic cavitary form of disease have an unusually high mortality due to fatal hemoptysis. Patients with bilateral pulmonary infiltrates and aspergillosis have a high mortality due to disseminated infection.

Dynamic upper airway imaging during awake respiration in normal subjects and patients with sleep disordered breathing

The effects of respiration on upper airway caliber were studied using cine computed tomography (CT) in 15 normal subjects, 14 snorer/mildly apneic subjects, and 13 patients with obstructive sleep apnea. All subjects were scanned in the supine position during awake nasal breathing. Eight-millimeter-thick axial slices were obtained at four anatomic levels from the nasopharynx to the retroglossal region every 0.4 s during a respiratory cycle. Tidal volume measured from an integrated pneumotachograph signal was correlated with slice acquisition during inspiration and expiration to generate loops comparing upper airway area and tidal volume. In all three subject groups and at all anatomic levels studied, there were significant dimensional changes in upper airway caliber during the respiratory cycle. The major findings in this investigation include: (1) the upper airway was significantly smaller in apneic than normal subjects, especially at the retropalatal low and retroglossal anatomic levels; in apneic patients the airway had an anterior-posterior configuration unlike the normal airway, which had a horizontal configuration with the major axis in the lateral direction; (2) in all three subject groups, little airway narrowing occurred in inspiration, suggesting that the action of the upper airway dilator muscles balanced the effects of negative intraluminal pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Suspected pulmonary embolism: prospective evaluation with pulmonary MR angiography

PURPOSE

To prospectively evaluate three magnetic resonance (MR) imaging techniques for detection of pulmonary embolism.

MATERIALS AND METHODS

Eighteen patients in whom the presence of acute or chronic pulmonary emboli was suspected underwent examination with the following pulse sequences: cardiac-gated spin echo, cine spatial modulation of magnetization, and two-dimensional time-of-flight pulmonary breath-hold (PBH) MR angiography. Three radiologists independently and blindly reviewed each case and graded a total of 518 arterial segments for each pulse sequence with a continuous scale of 0%-100% for likelihood of pulmonary embolism.

RESULTS

The overall sensitivity of PBH MR angiography for detection of acute pulmonary emboli was 0.85; for chronic emboli, which were smaller in anteroposterior (AP) diameter, the overall sensitivity was 0.42. Emboli larger than 1 cm in AP diameter were typically identified with > 75% confidence with all pulse sequences.

CONCLUSION

Acute pulmonary emboli greater than 1 cm in AP diameter were as accurately identified on PBH MR angiograms obtained in 15 seconds as they were on MR images obtained with longer pulse sequences not dependent on breath holding.

Dynamic imaging of the upper airway during respiration in normal subjects

The present study was conducted to determine the effects of quiet respiration on upper airway caliber in 15 normal subjects by using cine computed tomography. The cine computed tomography (Imatron) scanner was programmed to obtain 8-mm-thick axial slices every 0.4 s during inspiration and expiration at four anatomic levels, from the nasopharynx to the retroglossal region. Airflow (pneumotachograph) was measured, and tidal volume was obtained by integration. Upper airway area, determined by an objective edge detection algorithm, was plotted as a function of tidal volume to generate a loop describing upper airway area changes at each level during a respiratory cycle. The results demonstrate a 17% change in airway size across all anatomic levels during respiration. The maximum upper airway cross-sectional area at all four anatomic levels was significantly greater during expiration than during inspiration. Other major findings include 1) upper airway cross-sectional area decreases slightly during early inspiration, enlarges toward end inspiration, and is larger at end inspiration than at the beginning of inspiration; 2) upper airway cross-sectional area enlarges from end inspiration to the first point in expiration; the airway enlarges further, reaching its maximum early in expiration, and then narrows toward end expiration; and 3) the changes in upper airway dimensions during resting tidal breathing are greater in the lateral than in the anteroposterior direction. The data suggest that during inspiration, the action of negative intraluminal pressure may be largely balanced by the action of the upper airway dilator muscles, whereas during expiration, positive intraluminal pressure produces expansion of the upper airway.

Evaluation of pulmonary vascular anatomy and blood flow by magnetic resonance

Rapidly evolving magnetic resonance (MR) imaging techniques provide noninvasive approaches to evaluating morphology and quantitative physiologic information about blood flow in the pulmonary circulation. Important clinical applications currently include the preoperative and postoperative evaluation of congenital abnormalities, assessment of vascular involvement by extrinsic and intrinsic tumors, identification of central thromboemboli, and diagnosis of vascular lung lesions. Ongoing refinements in pulmonary MR angiography may make it possible to use the technique for the noninvasive detection of acute pulmonary emboli in the near future. Quantitative measurements based upon MR flow-encoding sequences are promising for the evaluation of patients with abnormal degrees or distributions of pulmonary blood flow, for example, those with unilateral lung transplants or pulmonary arterial stenoses. MR contrast agents currently under development also show promise for quantitative measurements of regional pulmonary ventilation and perfusion. The coupling of high-resolution anatomic and functional images renders MR a uniquely attractive and powerful method for evaluating the pulmonary vasculature.

The spectrum of pulmonary aspergillosis

Aspergillus species can produce a wide range of pulmonary disorders. Classically, pulmonary aspergillosis has been categorized into invasive, saprophytic, and allergic forms, all of which differ in their manifestations and therapy. More recently, however, other types of infection by this fungus have been recognized that do not fit into these traditional categories; an example is semi-invasive (chronic necrotizing) aspergillosis. In fact, these forms have features that are intermediate between those of the invasive and saprophytic types. The various types of aspergillosis can be regarded as constituting a continuous spectrum, ranging from invasive disease in the severely immunosuppressed patient to hypersensitivity reactions such as allergic bronchopulmonary aspergillosis (and bronchocentric granulomatosis) in the hyperreactive patient. Between these extremes are chronic necrotizing disease seen in midly immunocompromised hosts, and the noninvasive aspergilloma, which is due to saprophytic growth within a previously diseased area of lung in an otherwise normal host. Other intermediate forms may be encountered, their behavior being determined by the host immune status in combination with the underlying lung morphology. The radiographic and clinical features of these various forms of pulmonary aspergillosis are reviewed, including the more recently reported forms of infection such as Aspergillus tracheobronchitis and aspergillosis associated with acquired immunodeficiency syndrome and cystic fibrosis. The proposed concept of a disease spectrum is emphasized.

Thymoma mimicking a thyroid mass

Two cases of ectopic cervical thymoma are presented. These cases both manifested as mass lesions at the thoracic inlet, displacing the trachea, and were originally misdiagnosed as thyroid masses. The masses had clinical features similar to those previously reported for cervical thymoma: preponderance in women, benign clinical course, and absence of myasthenic symptoms.

Pulmonary MR angiography utilizing phased-array surface coils

Magnetic resonance angiography of the pulmonary vasculature was evaluated in 12 subjects using breath-hold gradient echo scans and surface coils at 1.5 T. Flow-compensated GRASS, spoiled GRASS (SPGR), and WARP-SPGR sequences were utilized. Comparisons were made among flip angles of 10-60 degrees, slice thicknesses of 3-10 mm, and body coil as well as Helmholtz pair and phased-array multiple coils. With 30-40 contiguous slices encompassing the lung, intrathoracic vasculature was segmented using a UNIX/X-windows based package dubbed VIDA. Three-dimensional anatomy was visualized by a brightest voxel projection algorithm, following reduction of chest wall pixel intensities by an operator-interactive module. Both SPGR (30 degrees flip angle, 4 mm slice thickness) and WARPSPGR (15 degrees flip angle, 5 mm slice thickness) in combination with phased-array multiple coils provided the most satisfactory images, based upon observations by three radiologists and signal-to-noise ratio measurements. The MR angiograms visualized vessels as distal as sixth to seventh order branches. The technique was successfully applied to three patients with pulmonary embolism. The results of this study demonstrate that the pulmonary vascular tree can be imaged by MR angiography combining a high resolution technique utilizing phased-array multiple coils, fast gradient echo sequences with breath-holding, and postprocessing of the volumetric image data. The technique is attractive since it is noninvasive and provides a full three-dimensional portrayal of the pulmonary vasculature.

Asbestos-related chest diseases: plain radiographic findings

In summary, there are a wide range of pulmonary manifestations seen in asbestos-exposed individuals from pleural and parenchymal fibrosis to pleural and parenchymal malignancy. The chest roentgenogram has assumed an important role in the detection and surveillance of asbestos-related pleural and parenchymal changes.

Acute pulmonary edema induced by overdosage of phenothiazines

Three schizophrenic adults with previous histories of using phenothiazine derivatives developed acute pulmonary edema after taking large amounts of these drugs. The clinical manifestations included coma (three), hypothermia (two), tachycardia (two), miosis (two) and hypotension (one). All three patients underwent gastric lavage and were treated supportively. The fulminant pulmonary edema in the three cases resolved within 18 to 40 h. The etiology of pulmonary edema following overdosage of phenothiazines remains unknown. The authors hypothesize that the most likely pathogenesis is a drug-induced neurogenic pulmonary edema resulting from a disturbance of hypothalamic function.

Differential diagnosis of hepatic neoplasms: spin echo versus gadolinium-diethylenetriaminepentaacetate-enhanced gradient echo imaging

Early results are reported of hepatic neoplasms studied with dynamic gadolinium-diethylenetriaminepentaacetate (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). The purpose of this study was to evaluate the potential of the Gd enhancement pattern for characterizing these neoplasms and to compare the performance of spin-echo (SE) to SE plus dynamic Gd-enhanced gradient-echo (GRE) pulse sequences. Forty-two patients with hepatic neoplasms were examined at 1.5 T field strength. In each patient, short and long repetition time/echo time (TR/TE) SE images were obtained, followed by pre- and post-Gd-DTPA (0.1 mmol/kg body wt), single-slice, breath-hold (13 s/scan) GRE images, which were serially acquired less than or equal to 12 min postinjection. The patterns of contrast enhancement of the various hepatic lesions were documented and analyzed. The time to peak Gd signal enhancement-to-noise ratio (SE/N), contrast-to-noise ratio (C/N), contrast (defined as the signal intensity ratio [SIR]), as well as the peak values of these quantities, were determined. The C/N and SIR values on the short and long TR/TE SE and pre-Gd GRE images for all hepatic neoplasms were also obtained. The discriminating abilities (hemangiomas vs. malignant neoplasms) of these quantities were analyzed statistically. In addition, the impact of lesion characterization on the SE versus the SE plus the Gd-enhanced GRE scans was assessed by means of a blinded reader study. Malignant hepatic neoplasms could be differentiated from hemangiomas by visual inspection of their enhancement patterns (p = 0.0009), by the time to peak C/N on Gd-enhanced images (p = 0.0002), and by the magnitude of such peak (p = 0.02). Combined SE + Gd-enhanced GRE scans afforded minor, though statistically significant (p less than 0.01), improvement of the accuracy in differentiating benign from malignant hepatic neoplasms. Late scans (12 min post-Gd) may be particularly useful in identifying hemangiomas that, unlike other neoplasms, have a significant high signal of their enhancing portions on such images.

Evaluation of the upper airway in patients with obstructive sleep apnea

Multiple methods have been used to study the structure and physiological behavior of the upper airway (UA) in patients with obstructive sleep apnea (OSA). Valuable information may be obtained from the physiologic measurement of pressure and resistance along the UA, as well as from imaging techniques that include: direct or fiberoptic visualization, cephalometric roentgenograms, fluoroscopy, acoustic reflection, computerized tomography, and magnetic resonance imaging. This review summarizes the information that each of these methods has contributed to our understanding of the UA. The results obtained with these different methodologies have generally been complementary with structural narrowing being identified in the majority of patients with OSA. This narrowing is usually focal and located in the velopharyngeal or retropalatal segment of the UA. This is also the predominant site of initial UA collapse. Although obesity with enlargement of soft tissue structures is considered the predominant mechanism leading to UA narrowing, abnormal craniofacial development on a genetic or developmental basis plays an important contributory role.