Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging

In this experiment, Sprague-Dawley rats with elastase-induced emphysema were imaged using hyperpolarized (3)He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash-in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague-Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients.

A small animal model of regional alveolar ventilation using HP 3He MRI1

RATIONALE AND OBJECTIVES

The aim of this study was to establish a standardized procedure for the measurement of regional fractional ventilation in a healthy rat model as a baseline for further studies of pulmonary disorder models.

MATERIALS AND METHODS

The lungs of five healthy male Sprague-Dawley rats were imaged using hyperpolarized helium-3 magnetic resonance imaging. From these images, regional fractional ventilation was calculated and maps generated detailing the distribution of fractional ventilation in the lung. The 1.56 mm x 1.56 mm x 4 mm regions of interest were assigned on 5 cm x 5 cm field of view lung maps. Histograms were also generated showing the frequency distribution of fractional ventilation values. To compare fractional ventilation values between animals, the ventilation procedure was standardized to results from individual pulmonary function tests. Each animal's spontaneous tidal volume, respiratory rate, and inspiration percentage (percent of total respiratory cycle in inspiration) were used in their mechanical ventilation settings.

RESULTS

Results were similar among all five healthy rats based on examination of ventilation distribution maps and frequency distribution histograms. Mean (0.13) and standard deviation (0.07) were calculated for fractional ventilation in each animal. However, these values were determined to be influenced by slice selection, and therefore the maps and histograms were favored in analysis of results.

CONCLUSION

This study shows consistent results in healthy rat lungs and will serve as a baseline study for future measurements in emphysematous rat lungs.

Association of traditional risk factors with coronary calcification in persons with a family history of premature coronary heart disease: the study of the inherited risk of coronary atherosclerosis

BACKGROUND

Genetic factors strongly influence the risk of coronary heart disease (CHD), but their contribution to variation in coronary atherosclerosis beyond that measured by traditional CHD risk factors is uncertain.

METHODS

We recruited healthy subjects with family histories of premature CHD. We assessed traditional risk factors and performed electron beam tomography (EBT) to quantitate coronary artery calcification (CAC), a marker of coronary atherosclerosis. Persons with significant risk factors that included diabetes, total cholesterol >300 mg/dL, active cigarette smoking, and poorly controlled hypertension were excluded from the study. In this paper, we report on the relationship between traditional risk factors and CAC in this cohort.

RESULTS

The incidence of coronary calcification was significantly higher in this cohort than in the population-based Rochester Heart Study. In our cohort, most traditional risk factors were significantly associated with CAC on univariate analysis. On the other hand, in stepwise logistical regression, age and triglycerides were the only predictors of variation in CAC in men and accounted for only 30% of the variation; in women, age, body mass index (BMI), and triglycerides were the only traditional risk factors significantly associated with CAC variation and accounted for 22.2% of CAC variance.

CONCLUSIONS

In a cohort of subjects specifically selected for the characteristic of a family history of premature CHD, traditional risk factors accounted for less than one-third of the variation in CAC, and the most important predictors of CAC after age were plasma triglycerides. This supports the opinion that other inherited risk factors have important effects on the variation in coronary atherosclerosis and that the strategy of using EBT to phenotype clinically asymptomatic subjects with regard to coronary atherosclerosis may be a useful tool for identification of genes that are associated with CHD.

Demonstration of a compact compressor for application of metastability-exchange optical pumping of 3He to human lung imaging

Hyperpolarized gas magnetic resonance imaging has recently emerged as a method to image lungs, sinuses, and the brain. The best lung images to date have been produced using hyperpolarized 3He, which is produced by either spin-exchange or metastability-exchange optical pumping. For hyperpolarized gas MRI, the metastable method has demonstrated higher polarization levels and higher polarizing rates, but it requires compression of the hyperpolarized gas. Prior to this work, compression of hyperpolarized gas had only been accomplished using a large, complex and expensive apparatus. Here, human lung ventilation images are presented that were obtained using a compact compressor that is relatively simple and inexpensive. For this test, 1.1 bar-L of 15% hyperpolarized 3He gas was produced at the National Institute of Standards and Technology using a modified commercial diaphragm pump. The hyperpolarized gas was transported to the University of Pennsylvania in a holding field provided by a portable solenoid.

Accuracy of bedside chest hard-copy screen-film versus hard- and soft-copy computed radiographs in a medical intensive care unit: receiver operating characteristic analysis

PURPOSE

To compare the clinical diagnostic accuracy of hard-copy readings of screen-film bedside chest radiographs and both hard- and soft-copy readings of bedside chest computed radiographs obtained in a medical intensive care unit.

MATERIALS AND METHODS

Two samples of 95 cases were assembled from chest images obtained in 541 patients with either screen-film radiography or computed radiography. The cases were stratified according to the clinical problem for which the examination was ordered; the corresponding diagnosis was verified by a panel of two or three radiologists. Four radiologists blindly read the hard-copy images obtained with screen-film or computed radiography. Six months later, the radiologists read the computed radiographs by using an 8-bit, 1,684 x 2,048-pixel display. The data were analyzed by using multireader-multicase receiver operating characteristic (ROC) analysis of variance.

RESULTS

No statistically significant differences in the area under the ROC curve were found between any of the methods.

CONCLUSION

The results provide some justification for using bedside chest computed radiography and for reading soft-copy images from a high-quality display.

Multi-slice, breathhold imaging of the lung with submillisecond echo times

The signal from the lungs is heavily attenuated by T2 and T2 decay in standard MR images of the thorax. The authors utilized the capabilities of a prototype fast gradient system to develop a multi-slice gradient echo sequence that can obtain images with an echo time of 0.7 ms. Images acquired in a single breath-hold are free from respiratory motion artifacts and clearly display signal from lung parenchyma. The use of fast gradients makes short echo times possible without the use of nonstandard RF pulses and spatial encoding techniques and their associated limitations.

Asbestos-related radiographic abnormalities in elevator construction workers

Elevator construction workers are exposed to asbestos dust during construction and refurbishment work on older buildings. We screened a cohort of workers, all with greater than 20 yr of employment in the industry, with clinical examinations, chest radiography ("B" reader interpretations), and routine spirometry. Twenty of the 91 workers (22%) had evidence of pleural disease, but none of them had an interstitial process consistent with asbestosis. Of those with pleural thickening, 15 had bilateral circumscribed plaques and five had unilateral plaque formation. There were no cases of diffuse pleural thickening, benign pleural effusions, or mesothelioma identified in our cohort. The difference in the mean body mass index of those with pleural abnormalities (29.18 +/- 3.95) and those without (27.7 +/- 3.86) was not statistically significant (p = 0.135). We conclude that elevator construction workers have an increased risk for the development of asbestos-related pleural disease.

Diagnosis and imaging of gastrointestinal tract cancers

Recent trends in the diagnosis and imaging of cancers of the gastrointestinal tract include developments in screening for colorectal cancer and innovations in ultrasonography and magnetic resonance imaging of primary and metastatic hepatic tumors. Mathematical models suggest that screening for colorectal cancer will be as cost-effective as several other widely accepted screening programs, including the Papanicolaou smear for cervical cancer and screening mammography. There is considerable discussion regarding the relative roles of procedures such as fecal occult blood testing, sigmoidoscopy, colonoscopy, and radiology in screening strategies. The issue remains unsettled. In ultrasonography, the use of intraoperative ultrasound allows for the detection of more metastatic lesions in the liver than do preoperative computed tomography and ultrasound. Esophageal endoscopic ultrasonography has been used for the preoperative assessment of depth of invasion by esophageal cancer. The technique is limited in cases of stenotic cancer in which the endoscope cannot be passed through the lesion. Similarly, endorectal ultrasound can be used for staging of rectal cancer. Color Doppler ultrasound has been used for the evaluation of blood flow in relationship to hepatic neoplasms. Magnetic resonance imaging has been used not only for detecting liver tumors but also for differentiating between neoplasm and hemangioma.

Staging of renal carcinoma using magnetic resonance imaging at 1.5 Tesla

The preoperative magnetic resonance imaging (MRI) studies of 31 patients with surgically proven renal cell carcinomas obtained with a 1.5 Tesla unit were retrospectively reviewed to assess the accuracy of MRI for staging of tumor. According to the Robson classification 12 patients were found at surgery to have Stage I renal carcinoma, three patients had Stage II, ten had Stage IIIA, one had Stage IIIB, two had Stage IIIC, one had Stage IVA, and two had Stage IVB disease. Twenty-five (81%) of 31 patients were staged correctly by MRI. Clearly MRI showed venous tumor extension without the need for intravenous contrast administration. Also, MRI had a negative predictive value of 95%, and a positive predictive value of 100% for the evaluation of inferior vena cava tumor thrombus. At 1.5 Tesla MRI is an excellent staging modality in the preoperative evaluation of renal carcinoma. It is especially recommended in patients with equivocal computed tomography findings and in all patients with contraindications to the intravenous use of iodinated contrast material.

Successful localization of parathyroid adenomas by magnetic resonance imaging

Exploration of the neck for primary hyperparathyroidism is facilitated if the parathyroid glands can be localized preoperatively. Magnetic resonance imaging is a noninvasive and relatively safe procedure that is capable of distinguishing and differentiating small soft-tissue structures. Ten patients with primary hyperparathyroidism underwent preoperative diagnostic magnetic resonance imaging followed by cervical exploration. In 9 of these patients (90 percent), imaging correctly predicted the location of a single enlarged parathyroid gland, and in one patient the findings were misleading. All 10 patients proved to have single adenomas in orthotopic locations. Based on this early experience, magnetic resonance imaging appears to be a promising technique for preoperative localization of an enlarged parathyroid gland.

Tumor recurrence versus fibrosis in the female pelvis: differentiation with MR imaging at 1.5 T

Twenty-two women with previous malignancies of the pelvis were examined with magnetic resonance (MR) imaging. In 21 of 22 patients, the MR imaging findings were confirmed with laparotomy on transvaginal biopsy. Twelve of the 22 patients had recurrent tumors; ten had a localized fibrotic mass, and two were found to have coexistent local fibrotic masses and distant recurrence. In 11 of the 12 patients with recurrence, MR imaging demonstrated the recurrent tumor as an area of increased signal intensity on long repetition time, long echo time spin-echo pulse sequences. Signal intensity of localized fibrosis varied with the time since initial treatment. Separate signal intensity measurements for T1- and T2-weighted images were obtained in regions of interest in recurrent tumors, early fibrosis (1-6 months after first treatment), and late fibrosis (more than 12 months). Ratios of signal intensity of muscle to that of fat were calculated, and a statistical analysis (Student t test) was performed. On heavily T2-weighted pulse sequences, the differences in signal intensity between late fibrosis and recurrent tumors were statistically significant (P less than .001). MR imaging is useful in identifying recurrent pelvic neoplasm and distinguishing it from posttreatment fibrosis.

Painful sickle cell crisis: bone marrow patterns observed with MR imaging

Eleven patients with homozygous sickle cell anemia (SCA) undergoing painful crisis were studied with magnetic resonance (MR) imaging. The signal intensity of bone marrow was diffusely decreased in the axial and peripheral skeleton on short repetition time (TR)/echo time (TE) images and long TR/TE images, which suggested hematopoietic marrow hyperplasia and was confirmed by isotope marrow scans in five patients. Focal areas of further decrease in signal intensity were seen on short TR/TE images in 12 of the 14 (86%) painful joints and three of the five (60%) painless joints. In the painful joints, these focal areas converted to high signal intensity on long TR/TE images, presumably due to edema, which suggested acute marrow infarction. In the painless joints, these low-intensity focal areas remained as low signal on long TR/TE images, which suggested absence of edema and thus areas of old infarction or fibrosis. These results indicate that MR imaging may enable differentiation between acute and chronic marrow infarcts in patients with SCA and serve as a useful guide in monitoring and directing therapy.

Hematopoietic and fatty bone marrow distribution in the normal and ischemic hip: new observations with 1.5-T MR imaging

The conversion of hematopoietic to fatty marrow is known to correlate with physiologic decreases in intramedullary blood flow. To determine whether the chronology of conversion is altered in patients with hip ischemia, T1-weighted magnetic resonance (MR) images of the hips in 50 healthy people and 27 with documented avascular necrosis (AVN) were reviewed. The distribution of fatty (high-signal) versus hematopoietic (low-signal) marrow was noted with respect to age. All patients had fatty marrow in the femoral capital epiphysis and greater trochanter. Hematopoietic intertrochanteric marrow was seen in 95% (80 of 84) of femurs in control subjects less than 50 years old, but in only 12.5% (two of 16) of those in control subjects older than 50 years (P less than .005). Only 33% (19 of 57) of patients less than 50 years with AVN had predominantly hematopoietic intertrochanteric marrow (P less than .005). The early conversion to fatty marrow in most patients with AVN as depicted by MR imaging may be an effect of decreased vascularity of the proximal femur and may allow the identification of patients at increased risk for AVN.

MR imaging of double aortic arch

Magnetic resonance was used to demonstrate a double aortic arch in a patient initially noted to have a right aortic arch on chest radiography.

Vascular occlusions detected by magnetic resonance imaging

Early experience with magnetic resonance imaging (MRI) indicates that it is well suited as a noninvasive vascular imaging modality. Blood flow at physiologic velocities results in a low signal within the vessel lumen and this property allows the separation of flowing blood from surrounding soft tissues. While flow effects, aneurysms, and mural lesions have been emphasized in the literature, vascular occlusions have received less attention. We evaluated 21 patients with documented venous or arterial occlusions on a 0.12-T developmental resistive unit. Venous occlusions caused by thrombus generally appeared as focal regions of increased signal. In 3 of 10 cases the venous thrombus itself could not be identified but the absence of a low-signal lumen in a normal location confirmed the impression of thrombus. In 2 of 17 venous occlusions a rim of low signal was noted around the thrombus. Venous collaterals were commonly seen. Tumor thrombus tended to have signal characteristics similar to the main bulk of the tumor from which it arose. There were four arterial occlusions including two cases of emboli, one arteriosclerotic occlusion, and one case of tumor invasion. Vascular calcifications, clearly evident on plain radiographs, were not seen on MRI. MRI appears to be a potentially useful noninvasive means of detecting vascular occlusions.

Nongated cardiac magnetic resonance imaging: preliminary experience at 0.12 T

Nongated cardiac magnetic resonance imaging (MRI) has been reported previously to be inadequate for obtaining diagnostic information. This study explored the role of pulse sequence in the degradation of the nongated cardiac image. Images of diagnostic quality were obtained by using single spin-echo sequences with a very short echo time (10-20 msec TE) on a 0.12-T developmental MR unit. Marked degradation of the image was noted with longer TEs, and it is concluded that the previous unfavorable reports using a nongated technique may have been due to the longer TEs used in other units. Short-TE technique was used to examine 34 patients with a variety of cardiac diseases. Eleven patients had ventricular aneurysms. These cases showed thinning of the myocardium, and four of them showed increased signal within the aneurysm, perhaps related to regionally slower blood flow. Twenty patients had enlargement of one or more cardiac chambers. Three of these patients had thrombus within an enlarged chamber, which was readily identified on MRI. Twelve patients had left ventricular hypertrophy that was concentric in 11. One patient demonstrated asymmetric septal hypertrophy. All four pericardial effusions were low in signal intensity, but this was related to the pulse sequence used. Six patients had extrinsic masses displacing the heart and distorting the chamber contour. One patient showed intracardiac invasion of tumor; this finding was not evident on the CT. One patient with ventricular septal defect (VSD) and corrected transposition was scanned. In addition to identifying the VSD and chamber hypertrophy, the malposition of the great vessels at the base of the heart was seen. Four postoperative patients were scanned; wire suture artifact did not preclude imaging. In conclusion, diagnostic information can be obtained from nongated cardiac images provided that the TE is very short (10-20 msec). Although quantitative functional data are not available from nongated images, qualitative and diagnostic information is possible and may suffice in certain circumstances.

Magnetic resonance imaging of postoperative patients with metallic implants

Magnetic resonance imaging (MRI) examinations were reviewed in 10 postsurgical patients with metallic implants in the abdomen or pelvis. MRI scans in these patients were free of the streak artifacts commonly encountered in computed tomography. This represents a significant advantage in diagnostic imaging in postsurgical patients, and it suggests that MRI may be a valuable technique in the postoperative assessment of patients with extensive abdominal surgical clips or metallic prostheses.

MR imaging of the mediastinum: a retrospective comparison with computed tomography

Magnetic resonance (MR) imaging of the mediastinum was performed with a 0.12 T resistive magnet and compared with the results of CT. On T1 weighted images with partial saturation technique, soft tissue masses, lymphadenopathy, lipomatosis, and vascular anatomy were comparable with MR and CT imaging in 19 of 30 patients (63.3%). In the remaining 11 patients only slight differences between the two modalities were observed. Our experience suggests that MR imaging at low field strength is equivalent to CT in the morphologic assessment of the mediastinum without the need for administration of intravenous contrast medium or exposure to ionizing radiation.

Mediastinal computed tomography in myasthenia gravis

Thirty-six of 119 patients with myasthenia gravis examined by computed tomography for possible thymic mass had a thymectomy. The computed tomographic findings were compared to the findings of chest x-ray and linear tomography and then correlated with the surgical histopathologic results. Computed tomography detected all cases of thymoma or thymic enlargement due to hyperplasia. Chest x-ray correctly demonstrated 50% of thymomas present while linear tomography demonstrated 88%. Computed tomography was not able to distinguish between enlargement due to thymoma or hyperplasia unless calcification was present. The role of computed tomography is detailed and discussed in relationship to the other diagnostic modalities.