Evan K. Fram

Effects of turbulence on signal intensity in gradient echo images.

Although the appearance of laminar vascular flow in magnetic resonance (MR) images has been characterized, there is no general agreement about the effect of turbulent flow on MR signal intensity. This study uses a fast scan gradient echo pulse sequence to evaluate nonpulsatile turbulent flow in two different models. The first model simulated flow in normal vascular structure. It generated nonpulsatile, laminar and turbulent flow in straight, smooth-walled Plexiglas tubes. The second model simulated flow through a vascular stenosis. It generated nonpulsatile, laminar, and turbulent flow through an orifice. Velocities and flow rates ranged from low physiologic to well above the physiologic range (velocity = .3 to 280 cm/second, flow rate from .15 to 40 L/minute). Transition from laminar to turbulent flow was observed with dye streams. Turbulent flow in straight, smooth-walled vessels was not associated with a decrease in MR signal intensity even at the highest velocities and flow rates studied. The transition from laminar to turbulent flow through an orifice is not associated with a decrease in gradient echo signal intensity. As the intensity of the turbulent flow increases, however, there is a threshold above which signal intensity decreases linearly as turbulence increases (r = .97). This study suggests that flow in normal vascular structures should not be associated with decreased signal intensity in gradient echo images. Turbulent flow through areas such as valves, valvular lesions or vascular stenoses, may be associated with a decrease in gradient echo signal intensity.

Optimizing electrocardiograph electrode placement for cardiac-gated magnetic resonance imaging.

Electrocardiographs recorded in a magnetic field for cardiac-gating in magnetic resonance imaging (MRI) are complicated by blood flow-induced potentials. This study examines which lead of the standard 12-lead ECG maximizes the QRS while minimizing flow-induced interference. Twelve-lead ECGs were performed on normal volunteers (n = 9) and patients (n = 13) in and out of the bore of a 1.5 Tesla imaging magnet. The amplitude of the major flow-induced potentials was measured, and the vectors of largest induced potential and the QRS axis were plotted for each subject. ECGs obtained outside and inside the magnet were digitized and subtracted (in magnet ECG--out of magnet ECG = artifact ECG) and the peaks of the resultant curves measured. Superimposed potentials were largest in the early T wave and late S-T segment in leads I, II, V1, and V2, and smallest in III and AVF. A low-amplitude 7-to 10-Hz signal occurred in most leads. In the frontal plane, QRS axes and flow potential vectors were closely clustered. In the transverse plane, QRS axes generally followed leads V5 or V6, whereas the flow potential vectors followed leads V1, V2, or V3. The normal and patient groups did not differ. Although leads III and AVP showed the smallest superimposed potentials, V5, V6, or a left posterior chest lead may maximize QRS and reduce artifact most consistently. A 7- to 10-Hz frequency filter may help eliminate artifacts in some subjects.

Secretion of surfactant by rat alveolar type II cells: morphometric analysis and three-dimensional reconstruction

Secretion of surfactant by alveolar type II cells occurs by exocytosis and is stimulated by several mechanical and hormonal mechanisms, including beta-agonists. We examined the morphological correlates of this process by electron microscopy and by three dimensional reconstructions of rat lung alveolar epithelial type II cells before and after isoproterenol stimulation. Male rats were given a dose of isoproterenol 2 hours prior to anesthesia. The lungs were fixed by intratracheal instillation and lung tissue was processed by methods designed to enhance the retention of saturated phospholipids. The type II cells were evaluated by transmission and scanning electron microscopy and morphometry of the type II cells was performed. Three dimensional reconstruction of secretory events at the alveolar air border was also done. We observed a dose dependent increase in elliptical cell-surface pores averaging 0.2 X 0.4 micron in size on the alveolar luminal side of type II cells. Most often these pores were surrounded by an elevated area lacking microvilli and overlying an area of granular cytoplasm. The pores observed were about half the average diameter of the lamellar bodies and a deformation of that spherical secretory organelle was seen frequently. We conclude these cell-surface pores represent the structures through which surfactant is released by type II cells. During the secretion of lamellar bodies, deformation may be imposed at the restriction of the surface pores. This deformation could be important in the transformation of the lamellar material from an intracellular storage site to its active role on the alveolar surface.

Microcomputer-based Technique for 3-d Reconstruction and Volume Measurement of Computed Tomographic Images: Part 1: Phantom Studies

This paper presents a microcomputer-based technique that accurately quantifies volumes from computed tomographic (CT) scans of irregularly shaped objects as well as displaying 3-D reconstructions. The method uses standard CT film, allowing analysis of previous or outside CT studies. The planimetry method showed less than 5% error in measuring irregular 2-D areas larger than 6 mm2. The method is demonstrated to be significantly more accurate than spherical, ellipsoid, or rectangular geometric models in quantifying object volume by CT (P less than .001). With a single gantry angle, planimetry showed a two standard deviation error under 10% in measuring the volume of irregular objects compared with an error over 30% for ellipsoid models. The inaccuracy of the spherical model (80% error) and the rectangular prism model (192% error) renders them impractical to provide quantitative object volume. Microcomputer planimetry provides an accurate and versatile means to measure the volume and produce 3-D reconstructions of objects scanned with CT, and it has potential application in quantifying tumor response with CT and magnetic resonance imaging.

Three-dimensional reconstruction of tubular myelin.

The lipid and protein components of pulmonary surfactant are synthesized by alveolar type II cells and stored in their secretory granules, the lamellar bodies. Tubular myelin is a highly ordered surfactant structure that is lung specific and produced in the alveolar airspace. Recent work identified Ca2+, surfactant apoproteins A and B, and saturated phospholipids as necessary for tubular myelin structure and function. We have used serial ultrathin sections from fetal rat lungs and reconstructed the three-dimensional structure of tubular myelin. The spheres of tubular myelin we viewed were 2-3 microns in diameter and were surrounded by up to 20 lamellar bodies, each apparently simultaneously contributing material to the tubules. We measured a long-range symmetry of the tubules, which were folded about a central axis and showed a repeated crossing of individual tubes from one side to the other of the large structure. The tubes appeared closed on their outer edges and there was a delay in the penetration of tubules by cationic ferritin added to tissue slices containing the tubular myelin, although within a few minutes tracer appeared in the lumina and on the walls of the tubules. The three-dimensional images were compatible with existing views of tubular myelin.

Microcomputer-based technique for 3-D reconstruction and volume measurement of computed tomographic images. Part 2: Anaplastic primary brain tumors.

Serial computed tomography (CT) plays an integral part in monitoring effects of therapy for primary anaplastic brain tumors. Despite advances in CT technology, clinicians often cannot obtain accurate quantitative volume information to complement the qualitative assessment of tumor change. This paper presents a microcomputer-based method that provides both quantitative volume measurements and 3-D reconstructions of primary anaplastic brain tumors based on their hard copy CT or magnetic resonance imaging studies. The findings of this study demonstrate that planimetry is feasible for routine clinical use and is superior in accuracy to the spherical geometric model, which is shown to significantly overestimate tumor volume. The findings of 62 quantitative tumor studies (17 patients) showed a direct relationship between the total tumor volume and the volume of the hypodense intratumor core. There was no evidence of a relationship between the total tumor volume and the amount of peritumor low density (edema).

A phantom for testing ECG-gated computed tomography of the heart.

A mechanical phantom has been built to evaluate electrocardiographically gated computed tomography of the heart. The phantom simulates the heart in terms of cyclic changes in chamber dimensions and wall thickness. Rate and excursion are variable, and the cavity of the chamber can be filled with liquid contrast media of different degrees of radio-opacity. Preliminary experiments with a prototypic gating system are described.