Biomedical subjects

Orlando P Simonetti

Publications and source records attributed to Orlando P Simonetti.

At least 19 recordsLinked to original sources

PubMed2006

Cine delayed-enhancement MR imaging of the heart: initial experience.

This study was performed by using an institutional review board-approved protocol, with waived informed consent and HIPAA compliance. The purpose of this study was to preliminarily evaluate a cine delayed-enhancement (DE) pulse sequence for depiction of wall motion and myocardial scar extent during a single acquisition. The technique is based on inversion-recovery single-shot balanced steady-state free precession magnetic resonance imaging. Cine DE images were acquired in 26 patients (18 men, eight women; age range, 25-84 years; mean age, 61 years+/-13 [standard deviation]). Image contrast was consistent throughout each series. Overall (ie, with both readers' scores averaged), the cine DE imaging-depicted wall motion was scored correctly in 71% of myocardial segments. Scar extent was scored correctly in 76% of segments; in no patient was scarring missed. Cine DE imaging is a promising technique for simultaneous visualization of wall motion and myocardial scar extent.

Adult↗

PubMed2006

Multislice dark-blood carotid artery wall imaging: a 1.5 T and 3.0 T comparison.

PURPOSE: To compare two multislice turbo spin-echo (TSE) carotid artery wall imaging techniques at 1.5 T and 3.0 T, and to investigate the feasibility of higher spatial resolution carotid artery wall imaging at 3.0 T. MATERIALS AND METHODS: Multislice proton density-weighted (PDW), T2-weighted (T2W), and T1-weighted (T1W) inflow/outflow saturation band (IOSB) and rapid extended coverage double inversion-recovery (REX-DIR) TSE carotid artery wall imaging was performed on six healthy volunteers at 1.5 T and 3.0 T using time-, coverage-, and spatial resolution-matched (0.47 x 0.47 x 3 mm3) imaging protocols. To investigate whether improved signal-to-noise ratio (SNR) at 3.0 T could allow for improved spatial resolution, higher spatial resolution imaging (0.31 x 0.31 x 3 mm3) was performed at 3.0 T. Carotid artery wall SNR, carotid lumen SNR, and wall-lumen contrast-to-noise ratio (CNR) were measured. RESULTS: Signal gain at 3.0 T relative to 1.5 T was observed for carotid artery wall SNR (223%) and wall-lumen CNR (255%) in all acquisitions (P < 0.025). IOSB and REX-DIR images were found to have different levels of SNR and CNR (P < 0.05) with IOSB values observed to be larger. Normalized to a common imaging time, the higher spatial resolution imaging at 3.0 T and the lower spatial resolution imaging at 1.5 T provided similar levels of wall-lumen CNR (P = NS). CONCLUSION: Multislice carotid wall imaging at 3.0 T with IOSB and REX-DIR benefits from improved SNR and CNR relative to 1.5 T, and allows for higher spatial resolution carotid artery wall imaging.

Adult↗

PubMed2006

An unusual cause of susceptibility artifact in magnetic resonance imaging.

Magnetic susceptibility artifact has been documented with various implants and devices, which require appropriate identification with screening of patients prior to subjecting them to magnetic resonance examination. We performed cardiovascular magnetic resonance (CMR) examination of the aorta in a 24-year-old woman in the setting of repaired aortic coarctation, and found magnetic susceptibility artifact arising from the stomach in the absence of known susceptibility artifact-producing material in this region. Further history revealed that she had ingested a prenatal vitamin prior to imaging, prompting experimental analyses that led us to conclude that iron-containing vitamins may be a source of magnetic susceptibility artifact.

Adult↗

PubMed2006

Technical aspects of pediatric CMR.

Cardiac magnetic resonance (CMR) of the pediatric patient involves a unique set of technical challenges above and beyond those encountered in adult imaging. Anatomical structures are smaller, demanding greater spatial resolution; heart rates are high, demanding greater temporal resolution; and patients maybe sedated or uncooperative, rendering breath-hold imaging strategies useless. Despite these difficulties, CMR offers several advantages over other imaging modalities, including soft tissue contrast, lack of ionizing radiation, a capacity for true three-dimensional imaging, accurate flow quantification, and freely selectable imaging planes. These advantages and continued advances in MR hardware, software, and imaging techniques are bringing CMR into more widespread use in pediatric cardiology. This review is a summary of the primary techniques used in pediatric CMR for both congenital and acquired cardiovascular disease. The fundamentals of CMR pulse sequences and physiological synchronization of data acquisition are described, and imaging applications are reviewed. While the basic imaging sequences and techniques are common to both pediatric and adult CMR, some significant differences in imaging priorities and strategies are discussed.

Child↗

PubMed2006

Myocardial ischemia and right ventricular dysfunction in adult patients with sickle cell disease.

BACKGROUND AND OBJECTIVES: Patients with sickle cell disease (SCD) have multi-organ manifestations of microvascular disease, though cardiac manifestations have been poorly characterized in vivo. This study sought to characterize myocardial characteristics in adult patients with SCD. DESIGN AND METHODS: Twenty-two consecutive outpatients and 11 age-matched controls underwent magnetic resonance imaging to assess myocardial perfusion reserve as well as left and right ventricular size and function and myocardial iron. Computed tomography of the coronary arteries was performed to assess epicardial coronary stenosis. RESULTS: Three of 22 outpatients with clinically stable SCD and no controls had abnormal myocardial perfusion reserve limited to the subendocardium, consistent with microvascular disease. Coronary arteries were free of disease as detectable by computed tomography angiography. Myocardial T2* was normal in all subjects (29 +/- 5 ms, median 29 ms), consistent with absence of cardiac iron deposition despite a high prevalence of hepatic iron overload (liver T2* 14 +/- 9 ms, median 12.0 ms). SCD patients had right ventricular enlargement and dysfunction (right ventricular ejection fraction 45 +/- 15 in SCD patients vs. 58 +/- 5% in controls, p=0.001) even in the absence of overt pulmonary hypertension. INTERPRETATION AND CONCLUSIONS: A subset of adult SCD patients may have myocardial ischemia in the absence of infarcted myocardium, myocardial iron overload, or coronary artery disease. Right ventricular dysfunction is present in stable SCD patients, despite normal resting pulmonary artery pressures. These findings could represent under-recognized mechanisms for chest pain and mortality in this population, and warrant further investigation in SCD crises.

Adult↗

PubMed2005

Effect of inversion time on delayed-enhancement magnetic resonance imaging with and without phase-sensitive reconstruction.

PURPOSE: To evaluate the consistency and inversion time (TI) independence of phase-sensitive reconstruction (PSIR) delayed-enhancement (DE) MRI in a clinical setting. MATERIALS AND METHODS: Mid-ventricular short-axis DE images were acquired in 25 patients using three TIs: 1) optimized to null viable myocardium, 2) 50 msec less than optimal TI, and 3) 50 msec greater than optimal TI. At each TI, images were acquired with PSIR and without magIR. In each image, percent scar was computed as the ratio of nonviable to total pixels in the left ventricle (LV). RESULTS: In the magIR images, percent scar was 23% +/- 15% (optimal), 11% +/- 11% (short), and 22% +/- 15% (long). In PSIR images, percent scar was 25% +/- 15% (optimal), 22% +/- 15% (short), and 22% +/- 14% (long). Percent scar was significantly underestimated in magIR images with short TI, but no statistically significant difference in percent scar was observed at the optimal or long TIs. CONCLUSION: DE-MRI is a robust imaging technique for clinical use. PSIR provided consistent image quality independently of TI, at least over the range of TIs evaluated in this study. However, neither image quality nor scar appearance in the PSIR images was significantly different from that in the magIR images when TI was at or above the null point of viable myocardium.

Analysis of Variance↗

PubMed2005

Multi-contrast delayed enhancement provides improved contrast between myocardial infarction and blood pool.

PURPOSE: To develop and test a delayed-enhancement imaging method for improving the contrast between myocardial infarction (MI) and blood pool. MATERIALS AND METHODS: The T(2) of blood is significantly longer than that of acute or chronic MI. The proposed multi-contrast delayed-enhancement (MCODE) imaging method produces a series of images with both T(1) and T(2) weightings, which provides both excellent contrast between normal and infarcted myocardium, and between blood and MI. RESULTS: The subendocardial border between MI and blood pool was easily discriminated in the T(2)-weighted image. The measured MI-to-blood contrast-to-noise ratio (CNR) was better in the T(2)-weighted image than in the T(1)-weighted image (22.5+/-8.7 vs. 2.9+/-3.1, mean+/-SD, N=11, P<0.001, for True FISP, and 19.4+/-10.8 vs. 3.9+/-2.3, N=11, P<0.001, for Turbo FLASH). CONCLUSION: The MCODE method provides a significant improvement in the ability to easily discriminate subendocardial MI by providing a T(2)-weighted image with high contrast between blood and MI. MCODE should improve both the detection and accurate sizing of MI.

Contrast Media↗

PubMed2005

Preliminary investigation of respiratory self-gating for free-breathing segmented cine MRI.

Segmented cine MRI generally requires breath-holding, which can be problematic for many patients. Navigator echo techniques, particularly successful for free-breathing coronary MRA, are incompatible with the acquisition strategies and SSFP pulse sequences commonly used for cine MRI. The purpose of this work is to introduce a new self-gating technique deriving respiratory gating information directly from the raw imaging data acquired for segmented cine MRI. The respiratory self-gating technique uses interleaved radial k-space sampling to provide low-resolution images in real time during the free-breathing acquisition that are compared to target expiration images. Only the raw data-producing images with high correlation to the target images are included in the final high-resolution reconstruction. The self-gating technique produced cine series with no significant differences in quantitative image sharpness to series produced using comparable breath-held techniques. Because of the difficulties associated with breath-holding, the respiratory self-gating technique represents an important practical advance for cardiac MRI. , Inc.

Algorithms↗

PubMed2005

Motion-corrected free-breathing delayed enhancement imaging of myocardial infarction.

Following administration of Gd-DTPA, infarcted myocardium exhibits delayed enhancement and can be imaged using an inversion-recovery sequence. A conventional segmented acquisition requires a number of breath-holds to image the heart. Single-shot phase-sensitive inversion-recovery (PSIR) true-FISP may be combined with parallel imaging using SENSE to achieve high spatial resolution. SNR may be improved by averaging multiple motion-corrected images acquired during free breathing. PSIR techniques have demonstrated a number of benefits including consistent contrast and appearance over a relatively wide range of inversion recovery times (TI), improved contrast-to-noise ratio, and consistent size of the enhanced region. Comparison between images acquired using segmented breath-held turbo-FLASH and averaged, motion-corrected, free-breathing true-FISP show excellent agreement of measured CNR and infarct size. In this study, motion correction was implemented using image registration postprocessing rather than navigator correction of individual frames. Navigator techniques may be incorporated as well.

Algorithms↗

PubMed2004

Myocardial infarction: optimization of inversion times at delayed contrast-enhanced MR imaging.

Seventeen patients underwent magnetic resonance (MR) imaging for myocardial viability with a protocol approved by the institutional review board and gave written informed consent. Breath-hold cine inversion-recovery segmented k-space true fast imaging with steady-state precession sequence, referred to as inversion time (TI) mapping, was performed to determine optimal TI for myocardial infarction inversion-recovery imaging. From TI mapping, optimal TI was 180-315 msec 10-15 minutes after administration of 0.15 mmol/kg of gadolinium-based contrast material. At that optimal TI, relative signal intensity of infarcted myocardium compared with uninfarcted myocardium was maximal (mean +/- standard deviation, 297.8% +/- 86.5), whereas signal-to-noise ratio of uninfarcted myocardium was minimal (4.5 +/- 1.2). When applied to conventional myocardial infarction inversion-recovery imaging, optimal TI resulted in nulling of signal intensity of uninfarcted myocardium in all patients and in excellent conspicuity of infarcted myocardium in all nine patients with visible infarction.

Adult↗

PubMed2004

Magnetic resonance versus radionuclide pharmacological stress perfusion imaging for flow-limiting stenoses of varying severity.

BACKGROUND: Although magnetic resonance first-pass imaging (MRFP) has potential advantages in pharmacological stress perfusion imaging, direct comparisons of current MRFP and established radionuclide techniques are not available. METHODS AND RESULTS: Graded regional differences in coronary flow were produced during global coronary vasodilation in chronically instrumented dogs by partially occluding the left circumflex artery. Regional differences in full-thickness flow quantified using microspheres were compared with regional differences obtained with MRFP and radionuclide SPECT imaging (99mTc-sestamibi and 201Tl). Relative regional flows (RRFs) derived from the initial areas under MRFP signal intensity-time curves were linearly related to reference microsphere RRFs over the full range of vasodilation (y=0.93x+4.3; r2=0.77). Relationships between 99mTc-sestamibi and 201Tl RRFs and microsphere RRFs were curvilinear, plateauing as flows increased. The high spatial resolution of the MRI enabled transmural flow to be evaluated in 3 to 5 layers across the myocardial wall. Reductions in subendocardial flow were visually apparent in MRFP images for > or =50% reductions in full-thickness flow. Endocardial-to-epicardial gradients in MRFP flow increased progressively with stenosis severity, whereas transmural flow patterns in remote normally perfused myocardium remained normal. Flow reductions of > or =50% not identified by radionuclide imaging were apparent in MRFP full-thickness and transmural analyses. CONCLUSIONS: High-resolution MRFP can identify regional reductions in full-thickness myocardial blood flow during global coronary vasodilation over a wider range than current SPECT imaging. Transmural flow gradients can also be identified; their magnitude increases progressively as flow limitations become more severe and endocardial flow is compromised increasingly.

Animals↗

PubMed2004

Multislice first-pass myocardial perfusion imaging: Comparison of saturation recovery (SR)-TrueFISP-two-dimensional (2D) and SR-TurboFLASH-2D pulse sequences.

PURPOSE: To compare signal-to-noise ratio (SNR), contrast-to-noise (CNR) ratio, and diagnostic accuracy of a newly developed saturation recovery (SR)-TrueFISP-two-dimensional (2D) sequence with an SR-TurboFLASH-2D sequence. MATERIALS AND METHODS: In seven healthy subjects and nine patients with coronary artery disease (CAD), contrast-enhanced perfusion imaging (with Gd-DTPA) was performed with SR-TrueFISP and SR-TurboFLASH sequences. Hypoperfused areas were assessed qualitatively (scale = 0-4). Furthermore, SNR and CNR were calculated and semiquantitative perfusion parameters were determined from signal intensity (SI) time curves. Standard of reference for patient studies was single-photon emission computer tomography (SPECT) and angiography. RESULTS: The perception of perfusion deficits was superior in TrueFISP images (2.6 +/- 1.0) than in TurboFLASH (1.4 +/- 0.6) (P < 0.001). Phantom measurements yielded increased SNR (143 +/- 34%) and CNR (158 +/- 64%) values for TrueFISP. In patient/volunteer studies SNR was 61% to 100% higher and signal enhancement was 110% to 115% higher with TrueFISP than with TurboFLASH. Qualitative and semiquantitative assessment of perfusion defects yielded higher sensitivities for detection of perfusion defects with TrueFISP (68% to 78%) than with TurboFLASH (44% to 59%). CONCLUSION: SR-TrueFISP-2D perfusion imaging provides superior SNR and CNR than TurboFLASH imaging. Moreover, the dynamic range of SIs was found to be higher with TrueFISP, resulting in an increased sensitivity for detection of perfusion defects.

Adult↗

PubMed2004

Self-gated cardiac cine MRI.

The need for ECG gating presents many difficulties in cardiac magnetic resonance imaging (CMRI). Real-time imaging techniques eliminate the need for ECG gating in cine CMRI, but they cannot offer the spatial and temporal resolution provided by segmented acquisition techniques. Previous MR signal-based techniques have demonstrated an ability to provide cardiac gating information; however, these techniques result in decreased imaging efficiency. The purpose of this work was to develop a new "self-gated" (SG) acquisition technique that eliminates these efficiency deficits by extracting the motion synchronization signal directly from the same MR signals used for image reconstruction. Three separate strategies are proposed for deriving the SG signal from data acquired using radial k-space sampling: echo peak magnitude, kymogram, and 2D correlation. The SG techniques were performed on seven normal volunteers. A comparison of the results showed that they provided cine image series with no significant differences in image quality compared to that obtained with conventional ECG gating techniques. SG techniques represent an important practical advance in clinical MRI because they enable the acquisition of high temporal and spatial resolution cardiac cine images without the need for ECG gating and with no loss in imaging efficiency.

Algorithms↗

PubMed2004

Automated rectilinear self-gated cardiac cine imaging.

ECG-based gating in cardiac MR imaging requires additional patient preparation time, is susceptible to RF and magnetic interference, and is ineffective in a significant percentage of patients. "Wireless" or "self-gating" techniques have been described using either interleaved central k-space lines or projection reconstruction to obtain MR signals synchronous with the cardiac cycle. However, the interleaved, central line method results in a doubling of the acquisition time, while radial streak artifacts are encountered with the projection reconstruction method. In this work, a new self-gating technique is presented to overcome these limitations. A retrospectively gated TrueFISP cine sequence was modified to acquire a short second echo after the readout and phase gradients are rewound. The information obtained from this second echo was used to derive a gating signal. This technique was compared to ECG-based gating in 10 healthy volunteers and shown to have no significant difference in image quality. The results indicate that this method could serve as an alternative gating strategy without the need for external physiological signal detection.

Electrocardiography↗

PubMed2004

Comparison of ECG-gated rectilinear vs. real-time radial K-space sampling schemes in cine True-FISP cardiac MRI.

PURPOSE: To compare three k-space sampling schemes in cine True-FISP cardiac magnetic resonance imaging and to evaluate changes in calculated quantitative functional cardiac parameters as a function of underlying k-space sampling techniques. MATERIAL AND METHODS: Using a 1.5 T MR imaging system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany), three k-space data-sampling schemes: rectilinear (2.96 ms/1.58 ms/70 degrees /12 s TR/TE/FA/AcquisitionTime), and two radial k-space acquisitions, with filtered back-projection (RADIAL) (2.45 ms/1.25 ms/ 50 degrees /3.3 s TR/TE/FA/AT), and steady-state projection imaging with dynamic echotrain readout (SPIDER) (3.39 ms/1.62 ms/55 degrees /1.8 s TR/TE/FA/AT) of a True-FISP sequence were applied in 10 healthy volunteers. Long- and short-axis breath-hold series were acquired and signal-to-noise ratios (SNR) for blood and myocardium were determined, as was contrast-to-noise ratios (CNR). Quantitative cardiac functional analysis included: determination of end-systolic/end-diastolic volumes, ejection fraction, and left ventricular mass. Functional analysis was performed by two independent readers three times for each volunteer and k-space sampling strategy. Statistical analysis evaluated the accuracy of the measurements obtained from each of the three sampling techniques and the intra- and interobserver reliability. RESULTS: Intraobserver and interobserver reliability measures of functional data were homogeneous without statistically significant differences. Intraobserver correlation coefficients ranged from 0.94-0.99; interobserver correlation coefficients ranged from 0.97-0.99. Direct comparison of SPIDER- and RADIAL-sampled True-FISP sequences showed no statistically significant differences in measured functional parameters with interstudy correlation coefficients from 0.88-0.98. RADIAL and SPIDER images had better temporal resolution and were qualitatively judged to provide superior wall/blood border definition. Statistically significant differences were identified in each volumetric functional parameter when results from the rectilinear sampling acquisitions were compared with either radial or SPIDER sampling techniques. RADIAL and SPIDER results were consistently higher than volumetric measures obtained from the rectilinear data set. CONCLUSION: Employing faster sampling schemes led to enhanced signal homogeneity while maintaining the necessary CNR for estimation of functional cardiac parameters. Enhanced signal homogeneity and maintained CNR will most likely improve the accuracy of the cardiac functional parameter determination.

Adult↗

PubMed2003

MR imaging evaluation of myocardial viability in the setting of equivocal SPECT results with (99m)Tc sestamibi.

PURPOSE: To determine if contrast material-enhanced magnetic resonance (MR) imaging is useful for assessment of myocardial viability in patients with equivocal stress-rest results from single photon emission computed tomographic (SPECT) examination with technetium 99m sestamibi. MATERIALS AND METHODS: Twenty patients underwent stress-rest SPECT examinations with sestamibi. Results were considered equivocal for assessment of myocardial infarct on the basis of fixed perfusion defects that either had normal wall motion or exceeded any wall motion abnormalities. Patients then underwent (a). contrast-enhanced MR imaging for assessment of myocardial infarct and (b). cine MR imaging for assessment of wall motion. For image analyses, the left ventricle was divided into 14 segments. Wall motion and extent of infarct were assessed independently and compared. RESULTS: Forty-one segments were equivocal for infarct at SPECT, and most (21 of 41 [51%]) involved the posterior or inferior wall. Infarct was confirmed with MR imaging in 10 of 41 (24%) equivocal segments in eight patients (40%). An additional 29 segments in eight patients had infarct at MR imaging that was not suspected at SPECT, including segments in three patients with no clinical history of myocardial infarct prior to imaging. All cases of infarct except one that were equivocal or undetected with sestamibi at SPECT were nontransmural at MR imaging, and most of the unsuspected subendocardial infarcts (15 of 28 [54%]) had no associated wall motion abnormalities. CONCLUSION: Patients with radionuclide examination findings that are equivocal for infarct may benefit from contrast-enhanced MR imaging, particularly in the setting of nontransmural infarct.

Adult↗

PubMed2003

Clinical blood flow quantification with segmented k-space magnetic resonance phase velocity mapping.

PURPOSE: To evaluate the accuracy of segmented k-space magnetic resonance phase velocity mapping (PVM) in quantifying aortic blood flow from through-plane velocity measurements. MATERIALS AND METHODS: Two segmented PVM schemes were evaluated, one with seven lines per segment (seg-7) and one with nine lines per segment (seg-9), in twenty patients with cardiovascular disease. A non-segmented (non-seg) PVM acquisition was also performed to provide the reference data. RESULTS: There was agreement between the aortic flow curves acquired with segmented and non-segmented PVM. The calculated systolic and total flow volume per cycle from the seg-7 and the seg-9 scans correlated and agreed with the flow volumes from the non-seg scans (differences < 5%). Sign tests showed that there were no statistically significant differences (P-values > 0.05) between the segmented and the non-segmented PVM measurements [corrected]. Seg-9, which was the fastest among the three sequences, provided adequate spatial and temporal resolution (> 10 phases per cycle). CONCLUSION: Segmented k-space PVM shows great clinical potential in blood flow quantification.

Aged↗

PubMed2002

Cross-sectional magnetic resonance angiography is accurate in predicting degree of carotid stenosis.

Carotid stenosis is currently estimated using methods based on flow velocity or two-dimensional projection images. Manipulation of magnetic resonance (MR) images in three dimensions (3-D MR) allows for direct measurement of carotid artery cross-sectional luminal area. The objectives of this study were (1) to assess the accuracy of 3-DMR as a technique for estimating carotid artery stenosis, and (2) to compare 3-D MR results with estimates from duplex ultrasound sonography (DUS) and conventional angiography. Twenty-nine patients underwent rapid, contrast-enhanced MRA within 1 month prior to carotid endarterectomy to obtain 3-D angiographic images of the carotid bifurcation. From these data, post-processing software was used to generate a longitudinal axis through the center of the vessel along which orthogonal cross-sectional images were taken. Luminal area measurements at the location of tightest stenosis and the distal normal internal carotid artery were obtained and used to calculate percent area stenosis. Applying the same procedure, 18 en bloc, ex vivo carotid plaques served as the standard against which we compared in vivo 3-D MR measurements at the location of tightest stenosis. Percent stenosis comparisons between MRA, angiography, and duplex ultrasound were also made. Our results showed that the measurement of luminal area by 3-DMR is accurate in predicting the degree of carotid stenosis. Direct measurement of luminal area may overcome limitations inherent to methods that rely on flow velocities and two-dimensional views of the carotid vasculature. A larger prospective study is necessary to confirm the reliability of this technique.

Carotid Stenosis↗