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M J Lipton

Publications and source records attributed to M J Lipton.

At least 37 records · Page 2Linked to original sources
PubMed1994

Aprotinin for coronary bypass operations: efficacy, safety, and influence on early saphenous vein graft patency. A multicenter, randomized, double-blind, placebo-controlled study.

The purpose of this study was to evaluate the efficacy and safety of aprotinin in a U.S. population of patients undergoing coronary artery bypass grafting. Early vein graft patency rates were assessed by ultrafast computed tomography. A total of 216 patients at five centers were randomized to receive either high-dose aprotinin or placebo during the operation; 151 patients underwent primary operation, and 65 underwent repeat procedures. Total blood product exposures in the primary group were 2.2 per patient receiving aprotinin as compared with 5.7 per patient receiving placebo (p = 0.010). The repeat group had 0.3 exposures per patient receiving aprotinin as compared with 10.7 per patient receiving placebo (p = < 0.001). Consistent reductions in the percent of patients requiring donor red blood cells and in the number of units of platelets, fresh frozen plasma, and cryoprecipitate required were associated with the use of aprotinin in both primary and repeat groups. Mortality was 5.6% in the aprotinin group and 3.7% in the placebo group (p = 0.517). In the primary group, clinical diagnoses of myocardial infarction were made in 8.9% of patients receiving aprotinin as compared with 5.6% of the patients receiving placebo (p = 0.435). In the repeat group, infarctions occurred in 10.3% of patients receiving aprotinin and 8.3% of patients receiving placebo (p = 1.000). Secondary analysis of electrocardiograms and available enzyme data showed no significant difference in infarction rates between the treatment groups. There was no difference in clinically significant renal dysfunction. The early vein graft patency rates were 92.0% in the aprotinin group and 95.1% in the placebo group (p = 0.248). In this study, aprotinin was effective in reducing bleeding and blood product transfusion rates, and its use was not associated with an increase in complications. An adverse effect on early vein graft patency rates was not demonstrated, but the number of grafts assessed was insufficient for absolute conclusions in this regard.

Aprotinin↗
PubMed1994

Cardiac function. Quantification with magnetic resonance and computed tomography.

An integral part of cardiac imaging is the evaluation of cardiac function. The parameters measured are essential elements of cardiac diagnosis, patient management, and the estimation of prognosis. Both computed tomography and magnetic resonance can measure cardiac indices with an accuracy and reproducibility unrivaled by present clinical imaging methods; however, analysis times to calculate these variables are, at present, prohibitively lengthy, and automated methods are sorely needed. In this article, the authors review the progress being made to automate analysis and the functional parameters that can be measured by computed tomography and magnetic resonance; they conclude that both techniques can provide excellent information for cardiac diagnosis.

Echocardiography↗
PubMed1993

Computed tomography of liver tumors.

Computed tomographic (CT) scan acquisition speed, interscan delay time, and image quality have significantly improved during the past decade. Thus CT has become a standard against which newer techniques such as magnetic resonance imaging (MRI) are validated. Comparison between CT and other modalities, however, lack validity unless the protocol for each procedure is optimized. The authors emphasize the importance of correct CT contrast enhancement techniques in order to obtain reproducible and optimal anatomical information for defining liver tumor morphology, which will determine resectability. Three-dimensional reconstruction using contiguous volume imaging with appropriate enhancement of vessels and tumor also provides important preoperative evaluation for possible resection. Analysis of the hemodynamic status of the liver parenchyma and of the lesions within it is also possible with contrast-enhanced CT although rarely practiced. With appropriate scanning techniques, excellent anatomical and functional information is obtained simultaneously using CT, although histologic specificity often remains insufficient without biopsy.

Humans↗
PubMed1993

Magnetization transfer imaging of the abdomen at 0.1 T: detection of hepatic neoplasms.

Magnetization transfer (MT) techniques have been proposed as a method of increasing contrast in MR images. To evaluate the feasibility of MT imaging of the abdomen at 0.1 T and to assess the clinical utility of this technique, the authors studied tissue contrast with a gradient-echo pulse sequence and an MT sequence in four normal volunteers, and in 17 patients with known primary or secondary neoplasms of the liver. The MT technique increased contrast between the liver and other tissues such as spleen, skeletal muscle and subcutaneous fat. The technique also produced increased contrast between hepatic tumors and normal liver parenchyma in gradient-echo images.

Abdomen↗
PubMed1993

Magnetization transfer imaging of normal and abnormal liver at 0.1 T.

RATIONAL AND OBJECTIVES: Magnetization transfer (MT) contrast is a new technique that may improve contrast in magnetic resonance imaging. High-protein tissues have a greater MT effect, resulting in a decrease in signal intensity. This study evaluates the MT technique on normal and abnormal liver tissue on a low-field system. The magnitude of the magnetization transfer was studied to determine its effect on image visualization and tissue characterization. METHODS: Ten volunteers and 25 patients with benign and malignant liver pathology, including left lateral segment hepatectomy, were imaged on a 0.1 T system. Gradient-recalled-echo T2-weighted sequence pairs were obtained with and without MT pulse saturation. Signal intensity measurements were made using region-of-interest tracings in liver, spleen, skeletal muscle, fat, and selected liver pathology. Liver-to-lesion contrast ratios and conspicuity changes were analyzed. RESULTS: The average signal intensity decrease for normal liver was .27. Skeletal muscle demonstrated the greatest MT effect (.48), while fat showed minimal (.01) MT change. Two hemangiomas and two liver cysts showed a small MT effect (.13 and .02, respectively). Of the malignant lesions imaged, melanoma metastases showed a mean MT effect of .34, while hepatomas showed mean effect of .15. Edematous liver tissue had an intermediate mean effect of .18. CONCLUSIONS: While T2 sequences are more versatile for standard liver imaging, an MT sequence may be helpful for tissue characterization in specific imaging situations. Melanoma metastases and hepatomas demonstrated significant MT effect and increased conspicuity of the malignant lesions.

Adult↗
PubMed1993

Contrast bolus dynamic computed tomography for the measurement of solid organ perfusion.

RATIONALE AND OBJECTIVES: The authors have investigated the aortic responses to various intravenous bolus injections of nonionic and ionic contrast media and have presented data illustrating the potential of ultrafast computed tomography (CT) to quantify perfusion in the kidney, liver, and spleen. METHODS: Bolus Dynamics Study: Performed in 3 healthy dogs (weight: 35 kg to 36 kg). In 2 dogs, 15 mL of the nonionic agent iohexol and the ionic agent sodium-meglumine diatrizoate were injected at 5, 10 and 20 mL/sec via a venous catheter placed in the superior vena cava; the order of injection was alternated between the 2 dogs. In the third dog, 25 mL of iohexol 300 mg I/mL was compared with diatrizoate 370 mg I/mL with injection rates of 10 and 20 mL/sec. Computed tomography scanning at the level of the midabdominal aorta was performed using an ultrafast CT scanner. Time-density curves were drawn for regions of interest over the aorta, and gamma-variate fits performed. Perfusion Studies: Dynamic perfusion scans of the upper abdomen were performed in more than 50 patients. A dose of 25 mL of iohexol 300 mg I/mL was injected at 10 mL/sec via an intravenous cannula in the antecubital fossa, followed immediately by 25 mL of saline, at the same rate. Scanning was performed at a single level using an ultrafast CT scanner. Regions of interest were drawn and gamma-variate fits were applied to the vascular time-density curves. RESULTS: Bolus Dynamics: Excellent curve fits for aortic time-density curves were obtained. A 10-mL/sec versus a 5-mL/sec bolus produced an 8% higher peak density. Nonionic contrast increased the peak density by a mean of 6%, increased the area under the corrected time-density curve by a mean of 22%, and lengthened the increase time by a mean of 21%. Perfusion Studies: Values obtained were reproducible and correlated well with values predicted from inert gas washout techniques. CONCLUSIONS: Changes in the CT number in a region after an intravenous injection of contrast medium may be used to calculate blood flow per unit volume of tissue. Ultrafast CT offers sufficient data points for accurate calculation. The quality of the aortic bolus is of great importance. Nonionic media offer several important advantages: hemodynamic perturbation is minimized, and they are better tolerated at the high injection rates needed. Low-osmolality nonionic agents produce "better" curves than conventional high-osmolality ionic agents, all other factors being equal. The resulting data are relevant to intravenous digital subtraction angiography and indirect portography as well as to perfusion measurement. The technique of quantitative dynamic CT is theoretically applicable to any cross-sectional modality, notably magnetic resonance.

Animals↗
PubMed1993

Noninvasive imaging for the diagnosis and management of myocardial ischemia.

The past 10 years has seen a revolution in noninvasive cardiac imaging. UFCT and MRI can demonstrate cardiac anatomy in exquisite detail and have become our most accurate methods of measuring ventricular function. PET and MRS are giving insights into myocardial metabolism that were previously impossible in vivo. UFCT and MRI have also made progress in imaging the coronary arteries and bypass grafts. Although neither technique is in a position to rival coronary arteriography, the first steps have been made. Accurate quantification of coronary calcium is possible with UFCT and promises to be our most valuable noninvasive tool in the diagnosis and management of patients with asymptomatic disease. Myocardial perfusion has been assessed with 201TL imaging for years, but new radiopharmaceutical agents and advances in UFCT and contrast-enhanced MRI are likely to bring great improvements. Table 2 lists the current modalities and outlines their main advantages and disadvantages. Despite all this progress, there has been little change in clinical practice. Invasive procedures, i.e., cardiac catheterization or transesophageal echocardiography, are still being performed even when equivalent information can be obtained noninvasively. While limited availability may explain the scant use of PET and UFCT for cardiac imaging, in those centers where it is available, interest is still muted. The need to foster multidisciplinary interaction is real. If the benefits of this revolution are to be passed on to patients, there needs to be a greater willingness among physicians from different specialties to collaborate and to be more tolerant than has occurred in many centers to date. This will not only improve patient care but it will also provide an appropriate evaluation of new technologies. All are critical if we are to solve the continuing problems of ischemic heart disease.

Contrast Media↗
PubMed1992

Left ventricular segmental volume by conductance catheter and Cine-CT.

The ability of the conductance catheter method to measure left ventricular segmental and total volume was evaluated by comparison with the Cine-CT technique. In the seven dogs studied, 19 conductance catheter and simultaneous Cine-CT runs were obtained. High correlation coefficients were found for total volume and segmental volumes, except in the basal segment. However, in most cases there was a significant variability in slope and intercept between animals. Both methods are promising tools for estimating dynamic segmental left ventricular volume, each having specific advantages such as a continuous signal (conductance catheter) or anatomic detail (Cine-CT). However, the results also show the need for further improvement of both methods.

Animals↗
PubMed1992

Magnetic resonance imaging and ultrafast computed tomography in cardiac tomography.

Cardiac magnetic resonance imaging and ultrafast computed tomography have been available for several years. While both modalities have become established research tools, neither has gained much acceptance in everyday clinical practice. Continued development has made both techniques easier to use and far more versatile. For patients to benefit from these improvements, it is important that clinicians become more familiar with the current state of the art.

Contrast Media↗
PubMed1991

Left atrial volume determination by biplane two-dimensional echocardiography: validation by cine computed tomography.

Left atrial (LA) volume measurements have been made by the application of the method of discs (modified Simpson's rule) to orthogonal biplane atrial echocardiographic images. Validation of the technique has been suboptimal due to deficiencies of the reference standard, levophase angiography. To define the accuracy of echocardiography, we compared LA end-systolic volume by echocardiography in 27 patients with volumes by cine computed tomography (Cine CT), a highly accurate and validated method of measuring cardiac chambers. Echocardiographic tracings were made in the apical long-axis two- and four-chamber views. In patients with atria less than 300 ml, 14 had echoes performed prospectively, with optimization of LA size, while the remaining 10 were analyzed retrospectively. The volume of each slice was calculated and was then summated to obtain total volume. The correlation coefficient between two-dimensional echocardiography and Cine CT was r = 0.98, and it was r = 0.82 when patients with atria greater than 300 ml (n = 3) were excluded. Echocardiography underestimated Cine CT measurements by 23%. The slope of the prospective group was closer to unity than the slope of the retrospective group (p less than 0.001), and the correlation with Cine CT was slightly better for the prospective group (r = 0.88 versus r = 0.77). LA volume by two-dimensional echocardiography correlates closely with Cine CT, a more accurate method of volume determination, and gives valid measurements of LA volume. Efforts to maximize LA size during scanning limit inaccuracies of echocardiographic measurements of the left atrium.

Echocardiography↗
PubMed1991

Left and right ventricular diastolic function during acute pericardial tamponade.

The aim of the study was to determine the effect of acute pericardial tamponade on left (LV) and right ventricular (RV) intracavitary and transmural pressure-volume (P-V) relations and to assess the effect of changing blood volume during tamponade on LV and RV volumes. The experiments were done in 11 acutely instrumented anaesthetized dogs in which LV and RV volumes were determined by computed tomography (CT) (n = 5) and LV and RV diameters by sonomicrometry (n = 6). Pressures were measured in the pericardium (balloon transducer), in the aorta and in the ventricles. Incremental pericardial infusion (up to 180 ml) caused a progressive left and upward shift of the LV and the RV intracavitary P-V relationship. This shift was entirely due to increased pericardial pressure (PP). The induction of tamponade caused no change in the LV and RV transmural P-V relationship. During tamponade with ventricular filling pressures above 10-15 mmHg, blood volume expansion caused only minimal increase in LV and RV volumes. In conclusion, pericardial tamponade shifted the LV and the RV intracavitary diastolic P-V relation by increasing PP. However, there was no change in the transmural P-V relationship, indicating unchanged myocardial compliance. Volume loading caused only minimal increase in LV and RV volumes during tamponade.

Animals↗
PubMed1991

Computed tomography for patient management in coronary artery disease.

Computed tomography (CT) represents the optimum theoretical approach to x-ray imaging. This conclusion results from an awareness of CT's capacity to solve the fundamental limitation of all forms of x-ray imaging--the superimposition of anatomic structures. Because CT is potentially a fully three-dimensional method, this problem is addressed in a manner not subject to the risks, complications, and technical limitations of selective angiography, subtraction angiography, tomography, and other techniques. Ultrafast CT provides a broad spectrum of useful quantitative cardiac data during one minimally invasive procedure. Therefore, the optimism for cine CT imaging of the heart is well founded. Apart from the demonstration of anatomic structures in any reconstructed plane and in movie format, without the need for any form of electrocardiographic gating, this new generation of millisecond CT scanners offers a unique potential for measuring myocardial mechanics and perfusion. Myocardial integrity can be evaluated by measuring myocardial wall thickening, which is a sensitive indicator of blood flow. It can also be assessed by time-density changes derived from analyzing the passage of contrast medium through thin slices of myocardium. Feasibility studies have demonstrated that this should be possible in the clinical setting by use of fast CT scanning. The radiation exposure to the patient with cine CT is low and comparable to, or less than, that of conventional CT and 10-15% of that received during angiocardiography; therefore, it is not a practical limitation. Further clinical and research studies are needed to determine the future role of this exciting new modality in the diagnosis and management of patients with heart disease.

Chronic Disease↗
PubMed1990

Varying tracheal cross-sectional area during respiration in infants and children with suspected upper airway obstruction by computed cinetomography scanning.

An ultrafast cinetomography computed tomographic scanner (cine-CT) was used to evaluate infants and children (n = 15) with suspected obstruction of the larynx or trachea. One scan sequence provided a single image at each of eight cross-sectional levels (volume-mode study). Each study, lasting 224 ms, covered the distance between the supraglottic area and the carina. Each patient also underwent a "dynamic" study at a specific level of interest determined from the volume-mode study. Forty images within 2.3 s covered at least one respiratory cycle. The images were displayed as a closed-loop movie and dynamic changes in laryngeal and tracheal caliber with respiration were monitored and quantitated. Tracheal boundaries were outlined either by a trackball-guided cursor (freehand) or semi-automated computer edge detection, and cross-sectional areas and diameters were determined. Reproducibility was tested among three investigators' freehand drawings and two automated computer drawings, at the same and at varying image intensities. The coefficient of variation for the computer-assisted records (0.2%) was smaller than for the best freehand drawing (1.5%). Tracheal diameters were reproducible, but with greater intra-individual investigator variability. Four normal tracheas had close to published measurements with conventional CT scanners. Cine-CT gives objective tracheal dimensions and their variation during respiration; it provides good anatomical detail above the carina, and also of the extra- and intra-thoracic vessels if injected with contrast medium.

Adolescent↗