Magnetic resonance imaging of the thorax of three dogs.
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The purpose of the study was to implement a three-dimensional (3D) magnetic resonance (MR) angiographic technique with acquisition times on the order of 800 msec with use of a spoiled gradient-echo pulse sequence (repetition time, 1.60 msec; echo time, 0.65 msec) and bolus intravenous injection of contrast material doses as small as 6 mL. High-spatial-resolution conventional MR angiography performed with 30 mL of gadopentetate dimeglumine was the reference standard. As implemented, subsecond 3D MR angiography allowed temporal sampling that was rapid enough to depict short-lived processes, as illustrated in patients with shunts and dissections. With small contrast material doses and subsecond frame rates, it is also possible to measure pulmonary arteriovenous circulation times with this 3D MR angiographic technique.
A double-walled magnetic resonance (MR) imaging-compatible container with a flexible diaphragm was designed to hold freshly excised porcine heart-lung preparations. The saline contents simulate MR signal of an actual chest wall. Continuous evacuation keeps the lung inflated. A variety of experiments with different imaging modalities, including angiography, under close to in vivo conditions are feasible. Access to bronchial system and lung vessels allows for various studies.
Magnetic resonance (MR) imaging was performed in 10 children with intrathoracic disease. Entities imaged included mediastinal lymphoma and neuroblastoma, pulmonary metastases from hepatoblastoma and osteogenic sarcoma, hemorrhagic pleural effusion, and nonmalignant disease such as abscess, cystic fibrosis, and bronchogenic cyst. MR imaging was particularly valuable in delineating mediastinal and parenchymal masses from adjacent vascular structures without the need for contrast material enhancement. However, MR was insensitive to lesion calcification. Since pulmonary vessels give very low signal, differentiation of high-intensity pulmonary nodules from vessels is readily apparent. For similar reasons, MR was excellent in distinguishing endobronchial mucus plugs from peripheral pulmonary vessels.
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Currently, the effect of intrathoracoabdominal, extrapulmonary volume displacements (Vep) are not well understood. Various clinical conditions can lead to volume displacements caused by gas or liquid accumulations. To analyze the pressure and volume changes that occur by Vep, we used a mathematical model of chest wall and lung mechanics that accounts for static changes associated with rib cage, diaphragm, abdomen, and lungs. By solving the model equations, we obtained simulations of the pleural and abdominal displacements that clearly differentiate the mechanisms involved. When abdominal displacement occurs, the reduction in lung volume is less than that caused by an equal displacement in pleural space. Abdominal displacement produces an increased pressure that expands the rib cage significantly, whereas pleural displacement does not produce a comparable action. Furthermore, our model predicts the conditions under which the work of inspiration is expected to increase as a consequence of these displacements. Finally, an important distinction is predicted between abdominal displacements caused by gas or liquid accumulation. Although an abdominal gas displacement tends to decrease the resting lung volume, the weight effect of a liquid displacement tends to increase the resting lung volume by pulling down the diaphragm.