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E Atalar

Publications and source records attributed to E Atalar.

At least 55 records · Page 3Linked to original sources
PubMed1998

Catheter-tracking FOV MR fluoroscopy.

Recent improvements in intravascular magnetic resonance imaging techniques mandate an accurate method of monitoring the introduction of MR catheter probes into the vessel of interest. For this purpose, a novel imaging protocol and a display method have been designed. First, a roadmap 3D image data set with standard pulse sequences is obtained using an external imaging coil. Subsequently, using very narrow rectangular-FOV fast-spoiled gradient recalled (SPGR), a movie of the percutaneous placement procedure of an MR catheter probe is acquired at a rate of 7.3 frames/second. In this protocol, the probe is used to transmit RF pulses and receive MR signal. A computer program was written for image unwrapping and for displaying the unwrapped movie frames on the roadmap image. In an alternative protocol, the movie frames in two projection angles were acquired in an interleaved fashion. Frames were unwrapped and combined with a 3D roadmap and displayed on a Silicon Graphics workstation equipped with stereovision goggles. Using these methods, percutaneous catheter placement in a phantom and a dog was examined. In conclusion, a new visualization technique for MR catheter placement is proposed. Combining this technique with high resolution intravascular MRI techniques may result in a very useful diagnostic tool for the evaluation of atherosclerosis and other vessel diseases.

Algorithms↗
PubMed1998

Precision of myocardial contour estimation from tagged MR images with a "black-blood" technique.

RATIONALE AND OBJECTIVES: The authors determined whether blood presaturation of tagged magnetic resonance (MR) images affects identification of left ventricular endocardial borders. MATERIALS AND METHODS: Three healthy volunteers underwent MR imaging performed with a breath-hold segmented spoiled gradient-recalled-echo sequence with tissue tagging. Two saturation pulses (in the basal and apical regions) were used to generate black-blood images. Manual segmentation of endocardial contours on black-blood and white-blood images was performed independently by five observers. RESULTS: Endocardial borders were better identified on black-blood images compared with white-blood images, especially in the early systolic phases. Interobserver variability in contour estimation was significantly higher for white-blood images (P < .001) and was twice that for corresponding black-blood images during early systole. Contour variability appeared to be affected mainly by tag-to-myocardium contrast (P = .009) and myocardium-to-chamber contrast (P = .05). CONCLUSION: Blood presaturation of tagged MR images improves reliability of contour segmentation.

Adult↗
PubMed1998

Paradoxical hypotension during dobutamine infusion for myocardial perfusion scintigraphy.

AIM: Dobutamine as a predominant beta-1 agonist increases heart rate and myocardial contractility and at sufficient high doses, it also increases systolic blood pressure. This study was undertaken to describe instances of paradoxical hypotension during dobutamine infusion for TI-201 myocardial perfusion SPECT study and the relationship between scintigraphic findings and hypotension occurred during dobutamine infusion. METHODS: In 201 consecutive patients unable to perform adequate exercise, dobutamine TI-201 myocardial SPECT was performed. Dobutamine was infused starting from 10 micrograms/kg/min increasing to 40 micrograms/kg/min. Paradoxical hypotension was defined as a decrease in systolic blood pressure > or = 20 mmHg compared with baseline study. RESULTS: Paradoxical hypotension was observed in 40 patients (Group A) out of 201 (19.9%) while no significant change in systolic blood pressure was detected in the remaining 161 patients (Group B). Mean maximum fall in systolic blood pressure was 39 +/- 18 mmHg (range: 20-90). In 33 of 40 patients (83%) with paradoxical hypotension, scintigraphy was normal compared to 131 (81%) of the remaining 161 patients. In patients of Group A, angiography, echocardiography and tilt table tests were performed in 13, 11 and 6 patients respectively. Nine of 13 angiographic evaluations (69%), 10 of 11 echocardiographic evaluations (91%), all of the tilt table tests were normal. Additionally, all of the patients of Group A were clinically followed up at least 6 months after the myocardial perfusion scintigraphy. None of the patients had a cardiac event except one patient during the follow-up period. CONCLUSION: Paradoxical hypotension during dobutamine infusion for myocardial scintigraphy is not an uncommon finding and up to 19.9% patients may develop such hypotension. To maximize test safety, precautions should be taken during dobutamine myocardial stress test, since remarkable decrease in systolic blood pressure may occur. Unlike hypotension occurring with exercise test, hypotension response to dobutamine is not always a marker for coronary artery disease.

Adrenergic beta-Agonists↗
PubMed1997

Intravascular magnetic resonance imaging using a loopless catheter antenna.

Recently, intravascular catheter probes have been developed to increase signal-to-noise ratio (SNR) for MR imaging of blood vessels. Miniaturization of these catheter probes without degrading their performances is very critical in imaging small vessels such as coronary arteries. Catheter coils have a loop incorporated in their structure and have limitations in physical dimensions and electromagnetic properties. The use of a loopless intravascular catheter antenna is proposed to overcome these problems. The catheter antenna is essentially a dipole, which makes a very thin diameter possible, and its electronic circuitry can be placed outside the blood vessels without performance degradation. The theoretical foundation for the design and operation of the catheter antenna is presented. Several catheter antennae, as small as 1.5 French, were constructed and tested on phantoms and rabbits with great success. The catheter antenna has a simple structure and is easy to design, implement, and operate.

Animals↗
PubMed1997

Quantification and reduction of ghosting artifacts in interleaved echo-planar imaging.

A mathematical analysis of ghosting artifacts often seen in interleaved echo-planar images (EPI) is presented. These artifacts result from phase and amplitude discontinuities between lines of k-space in the phase-encoding direction, and timing misregistrations from system filter delays. Phase offsets and time delays are often measured using "reference" scans, to reduce ghosting through postprocessing. From the expressions describing ghosting artifacts, criteria were established for reducing ghosting to acceptable levels. Subsequently, the signal-to-noise ratio (SNR) requirements for estimation of time delays and phase offsets, determined from reference scans, was evaluated to establish the effect of estimation error on artifact reduction for interleaved EPI. Artifacts resulting from these effects can be reduced to very low levels when appropriate reference scan estimation is used. This has important implications for functional MRI (fMRI) and applications involving small changes in signal intensity.

Artifacts↗
PubMed1997

Signal-to-noise measurements in magnitude images from NMR phased arrays.

A method is proposed to estimate signal-to-noise ratio (SNR) values in phased array magnitude images, based on a region-of-interest (ROI) analysis. It is shown that the SNR can be found by correcting the measured signal intensity for the noise bias effects and by evaluating the noise variance as the mean square value of all the pixel intensities in a chosen background ROI, divided by twice the number of receivers used. Estimated SNR values are shown to vary spatially within a bound of 20% with respect to the true SNR values as a result of noise correlations between receivers.

Humans↗
PubMed1997

Effect of an additional atropine injection during dobutamine infusion for myocardial SPET.

The aim of this study was to examine the value of an additional atropine injection in patients who do not achieve an adequate heart rate during dobutamine infusion for myocardial perfusion SPET (single photon emission tomography). Patients undergoing dobutamine myocardial SPET who failed to achieve > or = 85% of their age-predicted maximal heart rate at the end of dobutamine infusion (D protocol) had a second dobutamine myocardial SPET study on a separate day with the addition of an atropine injection during the dobutamine infusion (D + A protocol). Twenty-nine patients were studied. 201Tl was used in 27 patients and 99Tc(m)-MIBI in two patients. All patients underwent coronary angiography and significant coronary artery disease was found in 19 of 29 patients. The mean heart rate obtained at the peak of dobutamine infusion in the D + A protocol was significantly higher than that in the D protocol (153.8 +/- 13.8 vs 117.5 +/- 15.3 beats min[-1]). The D + A protocol resulted in a higher diagnostic sensitivity for the detection of stenosed coronaries compared with the D protocol (87 vs 80%, P > 0.05) without changing the specificity (89% for both protocols). On the other hand, the frequency of side-effects and ECG changes during the D + A protocol was higher than that with the D protocol (32 vs 47). In conclusion, the addition of an atropine injection during dobutamine infusion resulted in a higher diagnostic sensitivity for identifying stenosed coronaries compared to dobutamine alone.

Adrenergic beta-Agonists↗
PubMed1997

Intravascular magnetic resonance imaging of aortic atherosclerotic plaque composition.

Magnetic resonance imaging (MRI) may be an excellent tool to define atherosclerotic plaque composition, but surface MRI (SMRI) suffers from a low signal-to-noise ratio and low resolution of arterial images. Intravascular MRI (IVMRI) represents a potential solution for acquiring high-quality in vivo images of atherosclerotic plaques. Isolated segments of 11 thoracic human aortas obtained at autopsy were imaged by IVMRI using an intravascular receiver catheter coil designed and built at our institution. Images obtained by IVMRI were compared with corresponding images obtained by SMRI and with histopathological aortic cross sections. The intensity of intimal thickness and plaque components was graded by IVMRI and histopathology using a score of 1 for mild, 2 for moderate, and 3 for severe intensity. IVMRI had an agreement of 75% with histopathology in fibrous cap grading (37.5% expected, kappa = 0.60, P < 0.001) and of 74% in necrotic core grading (39% expected, kappa = 0.57, P < 0.001). Intraplaque calcification was correctly graded by IVMRI in six of the eight plaques in which histopathology recognized calcium. The analysis of intimal thickness showed 80% agreement between IVMRI and histopathology (52% expected, kappa = 0.59, P < 0.001). IVMRI image features were similar to those of SMRI. In addition, IVMRI accurately determined atherosclerotic plaque size in comparison with histopathology and SMRI (slope = 1.25 cm2, r = 0.99, P < 0.001 for luminal area by IVMRI vs histopathology; slope = 0.97 cm2, r = 0.996, P < 0.001 for luminal area by IVMRI vs SMRI). IVMRI has the potential to provide important prognostic information in patients with atherosclerosis because of its ability to accurately assess both plaque composition and size.

Adult↗
PubMed1996

Human cardiac high-energy phosphate metabolite concentrations by 1D-resolved NMR spectroscopy.

We have developed a method that can measure high-energy phosphate metabolite concentrations in humans with 1D resolved surface-coil NMR spectroscopy. The metabolites are measured by phosphorus (31P) NMR spectroscopy, and the tissue water proton (1H) resonance from the same volume serves as an internal concentration reference. The method requires only the additional acquisition of a 1H data set, and a simple calibration, performed separately, to determine the ratio of the signal per proton to the signal per phosphorus nucleus. The quantification method is particularly useful for human cardiac spectroscopy, where it eliminates image-based tissue volumetry and the corrections for signal sensitivity and phase nonuniformity necessary in prior approaches. Corrections are introduced to account for blood and fat contributions to the spectra. The method was validated on phantoms of phosphate of varying concentrations and on the human calf muscle. In calf, the adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were 5.6 +/- 1.6 (mean +/- SD) and 26 +/- 4 mmol/kg wet wt, respectively. In normal heart, [ATP] was 5.8 +/- 1.6 and [PCr] was 10 +/- 2 mmol/kg wet wt. These values are in excellent agreement with prior NMR studies and biopsy data. The protocol is easily accommodated within existing 1D cardiac patient protocols, and the same approach is advantageous for eliminating tissue volumetry and sensitivity corrections when measuring concentrations by 2D and 3D resolved spectroscopy.

Adenosine Triphosphate↗
PubMed1996

High resolution intravascular MRI and MRS by using a catheter receiver coil.

Potentially important diagnostic information about atherosclerosis can be obtained by using magnetic resonance imaging and spectroscopy techniques. Because critical vessels such as the aorta, coronary arteries, and renal arteries are not near the surface of the body, surface coils are not adequate to increase the data quality to desired levels. A few catheter MR receiver coil designs have been proposed for imaging the walls of large blood vessels such as the aorta. These coils have limited longitudinal coverage and they are too thick to be placed into small vessels. A flexible, long and narrow receiver coil that can be placed on the tip of a catheter and will enable multi-slice high resolution imaging of small vessels has been developed. The authors describe the theory of the coil design technique, derive formulae for the signal-to-noise ratio characteristics of the coil, and show examples of high resolution cross-sectional images from isolated human aortas acquired by using this catheter coil. In addition, high resolution in vivo rabbit aorta images were obtained as well as a set of spatially resolved chemical shift spectra from a dog circumflex coronary artery.

Animals↗
PubMed1995

Regional heterogeneity of human myocardial infarcts demonstrated by contrast-enhanced MRI. Potential mechanisms.

BACKGROUND: Myocardial reperfusion is pivotal to the prognosis of patients with acute myocardial infarction. In these patients, coronary flow is generally assessed by angiography and tissue perfusion by tracer scintigraphy. This study was designed to examine whether magnetic resonance imaging (MRI) provides information on myocardial perfusion and damage beyond that supplied by angiography and thallium scintigraphy after acute myocardial infarction. METHODS AND RESULTS: Twenty-two patients with recent myocardial infarction had ECG, echocardiography, coronary angiography, and fast contrast-enhanced MRI. Twelve patients also had exercise thallium scintigraphy. Time-intensity curves obtained from infarcted and noninfarcted regions were correlated with coronary anatomy and left ventricular function. Two perfusion patterns were observed in infarcted regions by comparison with the normal myocardial pattern. All patients but 1 had persistent myocardial hyperenhancement within the infarcted region up to 10 minutes after contrast. In 10 patients, this hyperenhanced region surrounded a subendocardial area of decreased signal at the center of the infarcted region associated with coronary occlusion at angiography, Q waves on ECG, and greater regional dysfunction by echocardiography. Moreover, the extent and location of the MRI abnormalities correlated well with the extent and location of the fixed single-photon emission computed tomography thallium defects. CONCLUSIONS: Large human infarcts, associated with prolonged obstruction of the infarct-related artery, are characterized by central dark zones surrounded by hyperenhanced regions on MRI. Conversely, reperfused infarcts with less regional dysfunction have uniform signal hyperenhancement. The MRI hyperenhanced segment correlates well with the fixed scintigraphic defect in patients with acute myocardial infarction.

Angioplasty, Balloon, Coronary↗
PubMed1995

A magnetization-driven gradient echo pulse sequence for the study of myocardial perfusion.

A T1-weighted imaging pulse sequence for contrast-based studies of myocardial perfusion is presented and evaluated in phantoms and in vivo. The sequence is similar to spoiled gradient-recalled echo sequences except that nonselective preparatory RF pulses drive magnetization to steady state prior to image acquisition. Steady state is thus obtained in both tissue and blood resulting in a stable, homogeneous, and dark pre-contrast baseline. Tip angles and timings are chosen so that pixel intensity approximates a linear relation to 1/T1. The dynamic range of signal response to contrast agent concentration is greater than that of an inversion-recovery fast low angle shot sequence. The sequence proposed should be useful for myocardial perfusion studies.

Blood↗
PubMed1994

Minimization of dead-periods in MRI pulse sequences for imaging oblique planes.

With the advent of breath-hold MR cardiac imaging techniques, the minimization of TR and TE for oblique planes has become a critical issue. The slew rates and maximum currents of gradient amplifiers limit the minimum possible TR and TE by adding dead-periods to the pulse sequences. We propose a method of designing gradient waveforms that will be applied to the amplifiers instead of the slice, readout, and phase encoding waveforms. Because this method ensures that the gradient amplifiers will always switch at their maximum slew rate, it results in the minimum possible dead-period for given imaging parameters and scan plane position. A GRASS pulse sequence has been designed and ultra-short TR and TE values have been obtained with standard gradient amplifiers and coils. For some oblique slices, we have achieved shorter TR and TE values than those for nonoblique slices.

Algorithms↗
PubMed1992

Cardiac tagging with breath-hold cine MRI.

A method is presented for measuring myocardial deformation in a breath-hold with tagged cine MRI. Tagged cine images of human hearts are obtained in arbitrary oblique planes on a standard imager with as few as four heartbeats. The scan time has been reduced 16- to 64-fold from previous techniques.

Electrocardiography↗
PubMedDate not supplied

Accuracy of arterial pulse-wave velocity measurement using MR.

The performance of a one-dimensional MR technique for the estimation of pulse-wave velocity in the aorta was evaluated. An expression for the error in this estimate was formulated and verified both by simulation and by experiment. On the basis of this formulation, guidelines for increasing the efficiency of the acquisition were established. The technique was further validated by comparison with pulse-wave velocity measurements made with a pressure catheter. All data were acquired from a latex tube driven by a pulsatile flow system. MR measurements of pulse-wave velocity in the tube were found to be very reproducible in the presence of white noise. Measurements by other techniques were in good agreement, falling within 2 SD of the mean. Because of its sensitivity and spatial resolution, this technique shows promise for making spatially resolved estimates of vessel distensibility. This would allow assessment of diseases, such as atherosclerosis, that cause local changes in the material properties of the vasculature.

Aorta↗
PubMedDate not supplied

Intravascular MR-monitored balloon angioplasty: an in vivo feasibility study.

PURPOSE: To develop a new method for monitoring balloon angioplasty by using an intravascular magnetic resonance (MR) imaging technique. MATERIALS AND METHODS: Nine New Zealand White rabbits were used: seven for technique refinement, including surgery, device insertion, stenosis creation, and MR protocol development; and two for the final MR imaging of the balloon angioplasty. The in vivo experimental method involved insertion of a catheter antenna and a balloon catheter, via femoral arteriotomies bilaterally, into the target site of the upper abdominal aorta, where a stenosis was artificially created by binding a plastic cable tie. Then, the entire process of the dilation of the stenosis with balloon inflation was monitored under MR fluoroscopy. RESULTS: Catheter insertions were successful, and a 5-mm-long stenosis of the aorta was produced in all nine rabbits. Eight complete balloon angioplasty procedures were satisfactorily monitored and recorded, showing clearly the stenosis of the aorta at the beginning of the procedure, the dilation of the stenosis during the balloon inflation, and the complete opening of the stenosis after balloon dilation. CONCLUSION: Preliminary results of in vivo balloon angioplasty monitored with intravascular MR imaging are presented. MR fluoroscopy, based on the intravascular MR imaging technique, may represent a potential alternative to x-ray fluoroscopy for guiding interventional treatment of cardiovascular diseases.

Angioplasty, Balloon↗
PubMedDate not supplied

Angiotensin converting enzyme gene polymorphism and the risk and extent of ischemic heart disease among Turkish patients.

OBJECTIVE: To evaluate the effects of the angiotensin converting enzyme gene polymorphism on the presence and extent of coronary artery disease and myocardial infarction among Turkish patients. METHODS: In total 393 consecutive patients undergoing coronary angiography were evaluated for cardiac risk factors including the lipoprotein profile, lipoprotein (a), apoprotein B, and apoprotein A1 levels. The angiotensin converting enzyme genotype was determined by polymerase chain reaction. The extent of coronary atherosclerosis was determined from the angiograms using the Gensini and Leaman scores. RESULTS: The angiotensin converting enzyme genotype was found not to be associated either with coronary artery disease (odds ratio 0.81, P > 0.05) or with myocardial infarction (odds ratio 1.16, P > 0.05). Exclusion of high-risk individuals failed to reveal any association for these subgroups. Furthermore, there was no association between aneurysm formation and the genotype (P > 0.05). The lipid parameters were also not affected by the genotype (P > 0.05). However, the extent of coronary atherosclerosis determined by the Gensini score was related significantly to the genotype by multivariate analysis (P = 0.007). CONCLUSION: The DD genotype is not associated with coronary artery disease and myocardial infarction among these angiographically assessed Turkish patients, even when low-risk subgroups are analysed. Nonetheless, the extent of coronary atherosclerosis in patients with coronary artery disease is affected by their genotype.

Alleles↗