Kinematic analysis of left ventricular deformation in myocardial infarction using magnetic resonance cardiac tagging.

The Magnetic Resonance (MR) tagging technique provides detailed information about 2D motion in the plane of observation. Interpretation of this information as a reflection of the 3D motion of the entire cardiac wall is a major problem. In finite element models of the mechanics of the infarcted heart, an infarcted region causes motional asymmetry, extending far beyond the infarct boundary. Here we present a method to quantify such asymmetry in amplitude and orientation. For this purpose images of a short-axis cross-section of the ejecting left ventricle were acquired from 9 healthy volunteers and 5 patients with myocardial infarction. MR-tags were applied in a 5 mm grid at end-diastole. The tags were tracked by video-image analysis. Tag motion was fitted to a kinematic model of cardiac motion. For the volunteers and the patients the center of the cavity displaced by about the same amount (p = 0.11) during the ejection phase: 3.8 +/- 1.4 and 3.0 +/- 0.9 mm (mean +/- sd), respectively. Cross-sectional rotation and the decrease in cross-sectional area of the cavity were both greater in the volunteers than in the patients: 6.4 +/- 1.5 vs. 3.0 +/- 0.8 degrees (p < 0.001), and 945 +/- 71 vs. 700 +/- 176 mm2 (p = 0.02), respectively. In the patients, asymmetry of wall motion, as expressed by a sine wave dependency of contraction around the circumference, was significantly enlarged (p = 0.02). The proposed method of kinematic analysis can be used to assess cardiac deformation in humans. We expect that by analyzing images of more cross-sections simultaneously, the 3D location and the degree of infarction can be assessed efficiently.

[Contrast-enhanced magnetic resonance angiography]. / Contrastversterkte kernspinresonantieangiografie.

Contrast-enhanced magnetic resonance angiography (MRA) involves intravenous injection of a contrast medium that increases the signal intensity of blood by shortening its T1 value. With contrast-enhanced MRA the acquisition time is short (less than 40 s for the abdominal aorta and the iliac vessels) and the images obtained can be interpreted accurately. The contrast medium currently in use virtually never causes adverse effects and is not nephrotoxic. After obtaining a three-dimensional dataset projections can be made at will. In addition, the individual partitions should be evaluated. The postprocessing time is about 15 min per examination. Current clinical applications are diagnostic examination of (stenoses of) the aortic arch and its branches, the thoracic and abdominal aorta, the visceral vessels, the renal arteries and the peripheral arteries. The sensitivity and specificity of contrast-enhanced MRA in most studies amount to over 90%.

Relation between torsion and cross-sectional area change in the human left ventricle.

During the ejection phase, motion of the left ventricular (LV) wall is such that all myocardial fibers shorten to the same extent. In a mathematical model of LV mechanisms it was found that this condition could be satisfied only if torsion around the long axis followed a unique function of the ratio of cavity volume to wall volume. When fiber shortening becomes non-uniform due to cardiac pathology, this pathology may be reflected in aberration of the torsional motion pattern. In the present study we investigated whether the predicted regular motion pattern could be found in nine healthy volunteers, using Magnetic Resonance Tagging. In two parallel short-axis cross-sections, displacement, rotation, and area ejection were derived from the motion of tags, attached non-invasively to the myocardium. Information from both sections was combined to determine area ejection, quantified as the change in the logarithm of the ratio of cavity area to wall area, and torsion, represented by the shear angle on the epicardium. Linear regression was applied to torsion as a function of area ejection. The slope thus found (-0.173 +/- 0.024 rad, mean +/- S.D.) was similar to the slope as predicted by the model of LV mechanics (-0.194 +/- 0.026 rad). In conclusion, the relation between area ejection and torsion could be assessed noninvasively in humans. In healthy volunteers, the relation was close to what was predicted by a mathematical model of LV mechanics, and also close to what was found earlier in experiments on animals.

CT densitometry of the lungs: scanner performance.

OBJECTIVE: Our goal was to establish the reproducibility and accuracy of the CT scanner in densitometry of the lungs. MATERIALS AND METHODS: Scanner stability was assessed by analysis of daily quality checks. Studies using a humanoid phantom and polyethylene foams for lung were performed to measure reproducibility and accuracy. The dependence of the CT-estimated density on reconstruction filter, zoom factor, slice thickness, table height, data truncation, and objects outside the scan field was determined. RESULTS: Stability of the system at air density was within approximately 1 HU and at water density within approximately 2 HU. Reproducibility and accuracy for densities found for lung were within 2-3%. Dependence on the acquisition and reconstruction parameters was neglible, with the exceptions of the ultra high resolution reconstruction algorithm in the case of emphysema, and objects outside the scan field. CONCLUSION: The performance of the CT scanner tested is quite adequate for densitometry of the lungs.

Scanner conformity in CT densitometry of the lungs.

PURPOSE: To quantify inter- and intrascanner conformity in computed tomographic (CT) densitometry of the lungs. MATERIALS AND METHODS: With six scanners from four manufacturers, a lung densitometry protocol with several variations was applied for performance comparison. Phantoms included water, air, and a humanoid thorax phantom equipped with a dog lung and exchangeable pseudolungs of polyethylene foam. RESULTS: All scanners produced acceptable CT numbers (Hounsfield units) for water, but some not for air. An incorrect calibration of air density affected all CT numbers at lung densities, but the error was easily correctable. Some systems were more sensitive to object size than others were. Sensitivity of CT numbers to section thickness, reconstruction filter, zoom factor, and table height was small, except for two scanners in relation to section thickness. CONCLUSION: After correction for poor air calibration, scanner conformity was acceptable when the reproducibility of lung densitometry in clinical practice was set as a reference.

The nonlinear partial volume effect and computed tomography densitometry of foam and lung.

A quantitative study was performed to assess the magnitude of the nonlinear partial volume effect (NLPVE) in computed tomography (CT) densitometry of polyethene foam and lung. This effect arises in materials having density variations on the scale of the sampling area of an individual CT-detector element. It causes a systematic underestimation of the density determined with CT. Foam samples and a resected lung of a goat were imaged with high resolution (20 lp/mm) using a mammography system, and the observed optical density variation in the images was converted into a distribution of pathlengths that x rays penetrate within the solid component of the cellular material. The obtained pathlength distribution was used to calculate the transmission, as seen by a single detector in computed tomography. Comparison with the transmission through homogeneous material of the same thickness gave an estimate of the NLPVE. For the foams studied, the CT-determined density was found to be too low by approximately 0.3%-0.5% due to this effect. Although these density errors are small, in calibrations of a CT scanner they may be of significance. For lung the underestimation of the density was less than 0.1%. These experimentally derived, NLPVE related CT-density errors are 32%-84% of those calculated from a simple model of a cellular solid.

Chronic obstructive pulmonary disease: evaluation with spirometrically controlled CT lung densitometry.

PURPOSE: To compare the computed tomographic (CT) lung densitometry results in patients with chronic obstructive pulmonary disease (COPD) and in control subjects (healthy persons). MATERIALS AND METHODS: Spirometrically gated CT sections at 5 cm above and 5 cm below the carina at 90% and 10% vital capacity (VC) were imaged in patients and controls. Various densitometric parameters were derived from the CT data, and results were compared between the two levels of inspiration. RESULTS: Densitometric results in patients with emphysema were substantially different from those in patients with chronic bronchitis and in controls at 90% and 10% VC. Differences in patients with chronic bronchitis and in controls were not significant at 90% VC but were significant at 10% VC (P < .001). The mean changes in densitometric parameters between 90% and 10% VC were substantially greater in controls than in patients with COPD. CONCLUSION: It may be possible to classify lung disease with only two CT sections obtained at the same anatomic level, one at 90% and one at 10% VC, irrespective of the densitometric parameter used.

Application of a mixed imaging sequence for MR imaging characterization of human breast disease.

Single slice MR images were obtained from 9 normal breasts, 17 breasts with benign tumors, and 11 breasts with malignant tumors using an interleaved (mixed) spin echo (SE) inversion-recovery (IR) imaging sequence. SE and IR MR images were synthesized with variable repetition, echo and inversion times from the mixed sequence data. These images were used to qualitatively evaluate the contrast possibilities available when imaging the breast with MR imaging. Proton T1 and T2 relaxation times were determined for normal breast tissues and malignant and benign breast tumors from pure T1 and T2 images calculated using the mixed sequence data. The mean T1 value in benign tumors of 1,049.02 +/- 40.31 was found to be significantly longer (p < 0.0001) than the mean value of malignant tumors (876.09 +/- 27.83) and normal tissues (795.64 +/- 21.12). The value of T2 in benign tumors (89.15 +/- 8.33) was significantly longer (p < 0.01) than the value of T2 in normal tissues (62.82 +/- 4.06). The mixed sequence can be applied to improve image contrast between malignant tumors, benign tumors, and normal tissues of the breast and can potentially differentiate between these tissues in vivo.

Magnetic resonance image appearance of hamartoma of the breast.

The magnetic resonance imaging (MRI) features of a breast hamartoma are presented. The hamartoma was evaluated using several imaging techniques with and without gadolinium-DTPA. This case demonstrates that, in selected cases, MRI is of value as an adjunct to mammography and sonography.

Breast disease evaluation with fat-suppressed magnetic resonance imaging.

Thirty patients with a variety of pathologically confirmed malignant and benign pathologic lesions of the breast were evaluated with a spectrally selective fat suppression imaging technique to obtain fat-suppressed images of the breast. The technique, a selective partial inversion-recovery (SPIR) method, demonstrated the architectural relationship of malignant and benign tumors with respect to the normal water-containing elements of the breast. These relationships included signs of advanced malignant disease such as tissue retraction, invasive growth, and multicentricity, which appeared on the fat-suppressed images. Fat-suppressed imaging provided useful information for assessing the breasts of both pre- and postmenopausal women, especially in the latter group, where fatty involution of the breast is common. Microcysts, which are normally not visualized by conventional methods, were demonstrated and associated with patients having confirmed fibrocystic disease of the breast. As expected, the SPIR technique did not improve the ability to distinguish between tissues having similar T1 and T2 relaxation time values, such as malignant tumors and normal breast parenchymal tissues. The technique was able to demonstrate that the intense lipid signal, known to be responsible for obscuring the borders of water-fat interfaces and small tumors, could be eliminated in a variety of pathological settings.

Clinical magnetic resonance spectroscopy of human breast disease.

Using image-guided volume-selection techniques, in vivo phosphorus-31 magnetic resonance (MR) spectroscopic profiles were obtained from 12 patients with malignant breast tumors, six patients with benign breast tumors, and nine volunteers with no underlying pathologic condition. Phosphatic metabolites identified in the spectral profiles included the phosphomonoesters (PME), inorganic phosphate (Pi), phosphodiesters (PDE), phosphorylated glycans (PG), phosphocreatine (PCr) and adenosine triphosphate (ATP). Based on the results of previous high-resolution ex vivo 31P MR spectroscopic analyses of breast tissues, the resonance of PG was identified in malignant and benign breast tumors. Malignant tumors were found to have a significantly (P less than .05) lower concentration of (PME + Pi) than normal breast parenchyma, and were distinguishable from both benign tumors and normal breast parenchymal tissue by significantly (P less than .01) elevated levels of (PDE + PG). 31P MR spectroscopy is the first technique potentially capable of differentiating among malignant breast tumors, benign breast tumors, and normal breast parenchymal tissues based on their in vivo phosphatic metabolic profiles.