Reduce Imaging Time Research Articles

Accelerated fluorine‐19 MRI cell tracking using compressed sensing

Cell tracking using perfluorocarbon labels and fluorine-19 (19F) MRI is a noninvasive approach to visualize and quantify cell populations in vivo. In this study, we investigated three-dimensional compressed sensing methods to accelerate 19F MRI data acquisition for cell tracking and evaluate the impact of acceleration on 19F signal quantification. We show that a greater than 8-fold reduction in imaging time was feasible without pronounced image degradation and with minimal impact on the image signal-to-noise ratio and 19F quantification accuracy. In 19F phantom studies, we show that apparent feature topology is maintained with compressed sensing reconstruction, and false positive signals do not appear in areas devoid of fluorine. We apply the three-dimensional compressed sensing 19F MRI methods to quantify the macrophage burden in a localized wounding-inflammation mouse model in vivo; at 8-fold image acceleration, the 19F signal distribution was accurately reproduced, with no loss in signal-to-noise ratio. Our results demonstrate that three-dimensional compressed sensing methods have potential for advancing in vivo 19F cell tracking for a wide range of preclinical and translational applications.

Adaptive retrospective correction of motion artifacts in cranial MRI with multicoil three‐dimensional radial acquisitions

Despite reduction in imaging times through improved hardware and rapid acquisition schemes, motion artifacts can compromise image quality in magnetic resonance imaging, especially in three-dimensional imaging with its prolonged scan durations. Direct extension of most state-of-the-art two-dimensional rigid body motion compensation techniques to the three-dimensional case is often challenging or impractical due to a significant increase in sampling requirements. This article introduces a novel motion correction technique that is capable of restoring image quality in motion corrupted two-dimensional and three-dimensional radial acquisitions without a priori assumptions about when motion occurs. The navigating properties of radial acquisitions-corroborated by multiple receiver coils-are exploited to detect actual instances of motion. Pseudorandom projection ordering provides flexibility of reconstructing navigator images from the obtained motion-free variable-width subsets for subsequent estimation of rigid body motion parameters by coregistration. The proposed approach does not require any additional navigators or external motion estimation schemes. The capabilities and limitations of the method are described and demonstrated through simulations and representative volunteer cranial acquisitions.

Rapid PROPELLER‐MRI: A combination of iterative reconstruction and under‐sampling

To develop a technique that is able to reduce acquisition time and remove uneven blurring in reconstructed image for PROPELLER MRI. By using under-sampling and iterative reconstruction, this proposed technique will be less sensitive to subject motion. Numerical simulations, as well as experiments on a phantom and healthy human subjects were performed to demonstrate advantages of a combination of under-sampled acquisition and iterative reconstruction. Method of motion correction was modified to increase accuracy of motion correction for the under-sampled PROPELLER acquisition. It was demonstrated that the proposed approach achieved substantial acceleration of PROPELLER acquisition while maintaining its motion correction advantage. An effective method for reducing imaging time in PROPELLER was introduced in this study, which minimizes typical under-sampling artifacts without uneven spatial resolution and maintains the ability of motion correction.

MO-D-213CD-02: Non-Contrast-Enhanced Magnetic Resonance Angiography Methods for Assessment of Morphology and Flow.

1. Understand the various origins of MRA contrast mechanisms that do not require a contrast agent. 2. Understand the issues related to NCE-MRA imaging including design, acquisition and processing. 3. Understand the benefits, pitfalls, and future potentials of these approaches. My research is sponsored by GE Healthcare.

Left Atrial scar assessment using imaging with isotropic spatial resolution and compressed sensing

Summary We assess left atrial scar using late gadolinium enhancement (LGE) with isotropic spatial resolution of 1.4mm 3 by using highly accelerated LOST [1] reconstruction. Background Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia [2]. Pulmonary vein isolation (PVI) using radiofrequency (RF)-ablation is the leading treatment for AF. Recently, LGE imaging of the LA has been used to identify atrial wall scar due to RF-ablation [3]. However, current LGE methods have limited spatial resolution that substantially impact assessment of scar in the complex geometry of PVs and LA. In this study, we sought to utilize prospective random k-space sampling and LOST [1] for accelerated LGE imaging, where reduction in imaging time was traded-off for improved isotropic spatial-resolution.

Reduced stress dose with rapid acquisition CZT SPECT MPI in a non-obese clinical population: Comparison to coronary angiography

BackgroundCadmium Zinc Telluride (CZT) SPECT camera technology has the potential to reduce patient’s radiation exposure and shorten imaging time. This study evaluated the correlation of low stress tracer dose, rapid CZT SPECT myocardial perfusion imaging (MPI) to coronary angiography in a <200-lbs population to further validate its ability to achieve both goals while preserving diagnostic accuracy. MethodsAll patients who had a low-dose stress (≤15 mCi) Tc-99m sestamibi SPECT MPI study using a CZT camera (GE Discovery NM 530c) with 3- to 5-minute image acquisition over a 2-year period followed by a coronary angiogram within 2 months were included. Patients with a history of coronary revascularization, left ventricular dysfunction, and LBBB or paced rhythms were excluded. Both MPI studies and coronary angiograms were interpreted by blinded readers and coronary artery disease (CAD) was defined as ≥70% stenosis. ResultsA total of 71 patients were included with a mean age of 64 years, 55% male, and a BMI of 25.4 kg/m2 with an average stress dose of 13.3 mCi. Exercise stress was performed in 54% of patients and vasodilator pharmacologic stress in 46%. Sensitivity was 89%, specificity was 66%, and accuracy was 78% for detecting obstructive CAD. ConclusionsIn this group of non-obese patients undergoing low stress dose imaging, high-efficiency CZT SPECT imaging demonstrated a high sensitivity, specificity, and accuracy for detecting obstructive epicardial CAD with a greatly reduced imaging time.

Ultra-fast in vivo x-ray microtomography of blowfly wingbeat

Ultra-fast in vivo x-ray microtomography of blowfly wingbeat

A parallel imaging approach to wide-field MR microscopy

Magnetic resonance microscopy, suggested in the earliest papers on MRI, has always been limited by the low signal-to-noise ratio resulting from the small voxel size. Magnetic resonance microscopy has largely been enabled by the use of microcoils that provide the signal-to-noise ratio improvement required to overcome this limitation. Concomitant with the small coils is a small field-of-view, which limits the use of magnetic resonance microscopy as a histological tool or for imaging large regions in general. This article describes initial results in wide field-of-view magnetic resonance microscopy using a large array of narrow, parallel coils, which provides a signal-to-noise ratio enhancement as well as the ability to use parallel imaging techniques. Comparison images made between a volume coil and the proposed technique demonstrate reductions in imaging time of more than 100 with no loss in signal-to-noise ratio or resolution.

Myocardial perfusion imaging: achieving high image quality in half the time or in half the radiation dose

Myocardial perfusion imaging (MPI) using SPECT has been extensively utilized in the management of patients with suspected or known coronary artery disease for at least two decades [1,2]. Since then, slow progression has been made in updating g‐camera design and in advancing software to improve processing speed and to quantitatively assess imaging. However, during recent years, significant efforts have been made by the industry and academic research to develop novel technologies; the first new software that advanced image reconstruction techniques and the second in innovative technology of nuclear systems incorporating cadmium zinc telluride (CZT) crystals as detectors that result in a dramatic increase in counting statistics [3,4]. The routine use of MPI has some limitations; one is the prolonged imaging time compared with other modalities such as CT angiography, and a second is the exposure to ionizing radiation by the radiopharmaceutical used. This editorial will discuss the technological advances that have been developed recently to cope with these limitations, including the reduced imaging time and the reduction in radiation dose, both with preserved image quality.

Optimum Two-Dimensional Uniform Spatial Sampling for Microwave SAR-Based NDE Imaging Systems

Microwave imaging systems for nondestructive evaluation, based on 3-D synthetic aperture radar (SAR) techniques, utilize either a real aperture, composed of many antennas mounted next to one another, or a synthetic aperture, generated by raster scanning a single antenna. To obtain a quality SAR image, the spatial sampling must be dense enough to accurately sample the electric field reflected from a target. Conversely, the quantity of spatial samples may be optimally reduced, resulting in reduced system complexity and required resources for systems employing real apertures and reduced imaging time for synthetic aperture systems. In the literature, it has been reported that the optimum sampling step size is equal to the theoretical resolution, as per the Nyquist rate. It has also been reported that an image generated using a sampling step size equal to the theoretical resolution may not possess the same spatial resolution as predicted. Also, as expected and reported, resolution is dependent upon the distance between the target and the aperture, aperture dimensions, and antenna beamwidth. However, existing formulations of SAR resolution do not account for all of the physical characteristics of a measurement (e.g., 2-D limited-size aperture, electric field decreasing with distance from the measuring antenna, etc.). This paper presents a theoretical formulation of resolution and a study into optimum uniform spatial sampling by analyzing simulated 3-D SAR images according to metrics representing image quality, namely, half-power resolution and RMS error between practically sampled images and an ideally sampled image. The results of this simulation demonstrate optimum sampling given design requirements that fully explain resolution dependence on sampling step size. Also, it is found that there is additional widening of the 2-D spectral estimation of the data due to the aperture-limited nature of the measurements, which further influences the choice of sampling step size. Subsequently, the simulated results are compared to experimental results corroborating the efficacy of the formulation. Finally, design curves and procedures are proposed for selecting sampling step size as per resolution requirements.

Performance Analysis for Magnetic Resonance Imaging With Nonlinear Encoding Fields

Nonlinear spatial encoding fields for magnetic resonance imaging (MRI) hold great promise to improve on the linear gradient approaches by, for example, enabling reduced imaging times. Imaging schemes that employ general nonlinear encoding fields are difficult to analyze using traditional measures. In particular, the resolution is spatially varying, characterized by a position-dependent point spread function (PSF). Likewise, the use of nonlinear encoding fields creates an additional spatial dependence on the signal-to-noise ratio (SNR). Although the two properties of resolution and SNR are linked, in this work we focus on the latter. To this end, we examine the pixel variance, which requires a computation that is often not feasible for nonlinear encoding schemes. This paper presents a general formulation for the performance analysis of imaging schemes using arbitrary encoding fields. The analysis leads to the derivation of a practical and computationally efficient performance metric, which is demonstrated through simulation examples.

Multiple passive element enriched photoacoustic computed tomography

Recently, we presented a method using laser-induced ultrasound from an external absorber (passive element) to image the ultrasound transmission parameters of an object under photoacoustic tomographic investigation. The method suffers from long measurement times due to the requirement for a large number of views and consequently physical projections around the object. Here we propose and validate an approach that permits a multitude of views to be obtained within a limited projection scenario. The approach uses a plurality of spatially distributed external absorbers in the path of the light, that results in multiple laser-induced ultrasound sources to interrogate the object from a number of angles. This reduces the required number of rotation angles or physical projections around the object, permitting a considerable reduction in imaging time without significant degradation in image quality. The approach brings the concept of hybrid imaging of ultrasound transmission parameters together with photoacoustic imaging, into the realm of practical application.

Zoom imaging for rapid aortic vessel wall imaging and cardiovascular risk assessment

To demonstrate the utility of a "reduced field-of-view" (zoom imaging) technique to accelerate free-breathing, ECG-triggered, turbo-spin-echo black-blood sequences, which have been previously described to detect subclinical aortic atherosclerosis. Fifteen healthy volunteers underwent MRI of the thoracic and abdominal aorta. Imaging with the conventional full field-of-view sequence was compared with zoom imaging. Total scan time, image quality (i.e., contrast-to-noise ratio and vessel wall sharpness) and vessel wall thickness were analyzed. A subgroup of 10 volunteers also underwent acceleration of imaging using sensitivity encoding (SENSE) for comparison. Zoom imaging significantly reduced imaging time from a mean of 41 ± 9 min (conventional imaging) to 15 ± 0.5 min (P<0.01). There was no difference in image quality between conventional and zoom imaging with respect to CNR (10.1 ± 6 versus 10.1 ± 6) or vessel wall sharpness (38 ± 4% versus 39 ± 4%). Furthermore, Bland Altman plots showed excellent agreement in vessel wall thickness measurements using the two methods. In comparison, SENSE not only reduced CNR but also resulted in underestimation of vessel wall thickness compared with the conventional sequence. Zoom imaging allows accurate and time-efficient imaging of the abdominal and thoracic aorta for cardiovascular risk prediction. In this application, it is preferable to SENSE.

SU‐C‐301‐03: A Spatially Distributed X‐Ray Source Array for High Resolution Digital Breast Tomosynthesis

Purpose: The current digital breast tomosynthesis (DBT) scanners are based on regular full‐field digital mammography systems and require partial isocentric motion of an x‐ray tube over certain angular range to record the projection views needed for reconstruction. This prolongs scanning time and degrades imaging quality due to motion blur. The purpose of this study is to evaluate the feasibility of improving spatial resolution and scanning speed of the current DBT device by replacing mammography tube with a stationary carbon nanotube (CNT) based x‐ray source array. Methods: A spatially distributed multi‐beam field emission x‐ray (MBFEX) source array was designed for DBT. Electrostatic simulations were carried out to design the electron focusing optics to achieve the desired x‐ray focal spot size. Finite element analysis was performed to determine the x‐ray source anode heat load. A control electronic system was developed to scan and to regulate the imaging dose from each beam by compensating the driving voltages and by modulating the exposure time from each beam. The x‐ray flux, lifetime, focal spot size, variation between different beams, etc were characterized. Results: A MBFEX source array with 31 individually controllable beams covering 30 degrees viewing angle was fabricated. It is operated up to 50KVp anode voltage and 30mA tube current per beam at an effective focal size comparable to that of the traditional mammography tube. Consistency in the beam‐to‐beam performance was achieved by optimizing the CNT cathodes and by electronic compensation. Tomosynthesis images of a breast phantom were obtained using the new source array. Conclusions: These preliminary results demonstrate the feasibility of CNT x‐ray source array for stationary DBT to eliminate image blurring from tube motion. With a fast detector the device can provide a higher spatial resolution at a reduced imaging time compared to the current rotating gantry DBT systems.This research is currently supported by the following grants&amp;#65306;NCI Grant No. U54CA119343, NIH R01 Grant No. CA134598‐01 and the University Cancer Research Fund at the University of North Carolina. Dr. Xin Qian, was supported by a fellowship from DoD Grant No. BC087505.

Image reconstruction from sparse data in synchrotron-radiation-based microtomography.

Synchrotron-radiation-based microcomputed-tomography (SR-μCT) is a powerful tool for yielding 3D structural information of high spatial and contrast resolution about a specimen preserved in its natural state. A large number of projection views are required currently for yielding SR-μCT images by use of existing algorithms without significant artifacts. When a wet biological specimen is imaged, synchrotron x-ray radiation from a large number of projection views can result in significant structural deformation within the specimen. A possible approach to reducing imaging time and specimen deformation is to decrease the number of projection views. In the work, using reconstruction algorithms developed recently for medical computed tomography (CT), we investigate and demonstrate image reconstruction from sparse-view data acquired in SR-μCT. Numerical results of our study suggest that images of practical value can be obtained from data acquired at a number of projection views significantly lower than those used currently in a typical SR-μCT imaging experiment.

Comparison of 250 MHz electron spin echo and continuous wave oxygen EPR imaging methods for in vivo applications

The authors compare two electron paramagnetic resonance imaging modalities at 250 MHz to determine advantages and disadvantages of those modalities for in vivo oxygen imaging. Electron spin echo (ESE) and continuous wave (CW) methodologies were used to obtain three-dimensional images of a narrow linewidth, water soluble, nontoxic oxygen-sensitive trityl molecule OX063 in vitro and in vivo. The authors also examined sequential images obtained from the same animal injected intravenously with trityl spin probe to determine temporal stability of methodologies. A study of phantoms with different oxygen concentrations revealed a threefold advantage of the ESE methodology in terms of reduced imaging time and more precise oxygen resolution for samples with less than 70 torr oxygen partial pressure. Above 100 torr, CW performed better. The images produced by both methodologies showed pO2 distributions with similar mean values. However, ESE images demonstrated superior performance in low pO2 regions while missing voxels in high pO2 regions. ESE and CW have different areas of applicability. ESE is superior for hypoxia studies in tumors.

Diagnostic Accuracy of 1.5-T Unenhanced Whole-Heart Coronary MR Angiography Performed with 32-Channel Cardiac Coils: Initial Single-Center Experience

To compare the imaging time and image quality obtained with whole-heart coronary magnetic resonance (MR) angiography performed with five- and 32-channel coils in healthy subjects and determine the accuracy of MR angiography performed with 32-channel coils in the detection of obstructive coronary artery disease (CAD). The institutional review board approved the study protocol, and all participants provided written informed consent. The authors studied 10 healthy subjects and 67 patients suspected of having CAD who were scheduled for coronary angiography. Unenhanced 1.5-T coronary MR angiography was performed with five- and 32-channel coils in healthy subjects and with 32-channel coils in patients. Clinically significant CAD was defined as a diameter reduction of at least 50% at coronary angiography. The sensitivity and specificity of coronary MR angiography were calculated. The mean imaging time was substantially reduced from 12.3 minutes ± 4.2 (standard deviation) with five-channel coils to 6.3 minutes ± 2.2 with 32-channel coils, with equivalent image quality scores. Acquisition of MR angiograms was completed in all 67 patients, with a mean imaging time of 6.2 minutes ± 2.8. The prevalence of CAD in the study population was 58% (39 of the 67 patients). The areas under the receiver operating characteristic curves as determined at vessel- and patient-based analyses were 0.91 and 0.90, respectively; the sensitivity and specificity at vessel-based analysis were 86% and 93%, respectively. Whole-heart coronary MR angiography performed at 1.5 T with 32-channel coils permits noninvasive detection of CAD with substantially reduced imaging time. This noninvasive approach can be an alternative to multidetector computed tomographic coronary angiography for ruling out obstructive CAD in patients who have a contraindication to contrast material and in young subjects who are at higher risk from ionizing radiation. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101323/-/DC1.

Diagnostic performance of 3T stress magnetic resonance myocardial perfusion imaging (MRMPI) using 32-channel cardiac coil in patients with coronary artery disease

Background/aim With newly available 32-channel cardiac coil, 3 tesla MRI system provides increased signal-to-noise radio (SNR), reduced imaging time and improved spatial resolution. This study sought to determine the diagnostic performance of 3T stress MRMPI with 32-channel cardiac coil in detecting clinical relevant coronary artery stenosis in comparison with invasive coronary angiography (ICA).

New Toys for Nuclear Cardiologists

Gordon Liljestrand is credited with establishing modern nuclear cardiology as a noninvasive imaging modality in 1939.1 Table summarizes major technological advancements in myocardial perfusion imaging over the past 70 years that have led to more accurate assessment of coronary artery disease (CAD). Most of these technical advances have involved radioisotopes and computer software. Camera hardware has undergone relatively little change since the introduction of the gamma camera, also commonly referred to as the scintillation camera, by Hal Anger in 1958.2 The gamma camera has performed admirably as the workhorse for myocardial perfusion imaging over the years but has several limitations. Sensitivity and resolution are modest. Imaging is inefficient as the heart occupies only a small portion of the field of view. Imaging places several demands on the patient, requiring relatively long imaging times (8 to 12 minutes) while lying motionless on a narrow, hard table with one or both arms fully abducted to minimize the distance between the patient's chest and the rotating detectors. The relatively long imaging times require administration of fairly high doses of radioisotopes with attendant higher radiation exposure, an issue of increasing medical and societal concern.3 View this table: Table. Developments in Nuclear Cardiology Article see p 51 In the past few years, there have been tremendous advances in gamma camera technology due to the replacement of the conventional sodium iodide (NaI)-based systems with solid-state detectors using cesium iodide coupled to photodiodes or novel semiconductor-based detectors using cadmium zinc telluride (CZT). The most promising of these new technologies is the CZT detector, which directly converts gamma radiation to an electronic pulse and thereby eliminates the need for a scintillating crystal and photomultiplier tubes. The CZT detector is substantially smaller than a NaI-based detector. In addition, the CZT detector offers substantially better energy resolution and spatial resolution than …

Assessment of left ventricular function: visual or quantitative?

Assessment of cardiac function continues to be an important issue in patients with assumed left ventricular (LV) dysfunction [1–10]. In particular in patients with enlarged left ventricles, such as occurs in ischemic and idiopathic dilated cardiomyopathy, accurate assessment of LV function remains pivotal [11–14]. To assess myocardial function, different diagnostic methods are currently performed such as echocardiography, single photon emission computed tomography (SPECT), and cardiac magnetic resonance imaging (CMR) [15–23]. In the clinical arena, detection of myocardial function is predominantly based on echocardiographic studies. In addition, nuclear techniques, showing preserved tracer uptake and metabolism in viable myocardium, may also assess left ventricular function and wall motion. Volumetric analysis by gated SPECT imaging offers considerable additional value to SPECT myocardial perfusion imaging in characterizing functional abnormalities thereby potentially improving test specificity [24–37]. Subsequent to echocardiography and gated SPECT imaging, CMR has now long been recognized as an accurate and reliable means of evaluating LV function. Considerable progress has been made in the field of CMR, providing accurate evaluation of LV function parameters in coronary artery disease, heart failure, hypertrophic cardiomyopathy, and many other cardiac diseases [38–49]. CMR may be more accurate than echocardiography and gated SPECT in establishing LV volumetric parameters because of its more objective analysis and superb spatial resolution, respectively [50–58]. In the current issue of the International Journal of Cardiovascular Imaging, Holloway et al. [59] nicely determined the accuracy of visual analysis of LV function in comparison with the accepted quantitative reference standard CMR. Cine CMR imaging was performed at 1.5 T on 44 patients with a range of LV ejection fractions (EF) between 5 and 80%. Eighteen clinicians were asked to visually assess LVEF after sequentially being shown cine images of a four-chamber (horizontal long axis), two-chamber (vertical long axis) and a short axis stack. The authors found strong correlations between visual and quantitative assessment. However, LVEF was underestimated in all categories (by 8.4% for horizontal long axis, 8.4% for horizontal long axis + vertical long axis and 7.9% for horizontal long axis + vertical long axis + short axis stack). LVEF was particularly underestimated in patients with mild LV dysfunction (17.4%, P < 0.01), less for moderate (4.9%) and not for severe impairment (1%). It was concluded that assessing more than one view of the heart improved visual assessment of LVEF. However, the 18 clinicians underestimated LVEF by 8.4% on average, with particular inaccuracy for those patients with mild LV dysfunction. Given the important clinical information provided by LV assessment, in particular in deformed left ventricles, the authors recommended quantitative analysis for accurate assessment of LV function. Several studies have compared visual and quantitative assessment of LVEF, both in normal subjects and patients with impaired LV function [60–68]. Nearly all studies showed that LVEF is underestimated by visual estimation compared with the quantitative assessment. Holman et al. [65], using a dedicated analytical software package (MASS version 1.0) including a modified centerline method and a new 3D-analysis approach, showed in 25 patients after acute myocardial infarction that the use of three-dimensional quantitative analysis of cine CMR images accurately quantifies the extent of regional LV dysfunction in the infarcted heart. Van der Geest et al. [66] evaluated a computer algorithm for the automated detection of LV endocardial and epicardial boundaries in time series of short-axis CMR images based on an Active Appearance Motion Mode. In 20 short-axis CMR examinations, manual contours were defined in multiple temporal frames (from end-diastole to end-systole) in multiple slices from base to apex. Global LV function results derived from automatically detected contours were compared with results obtained from manually traced boundaries. Automated contour detection resulted in small, but statistically non-significant, underestimations of LV volumes and mass: and an excellent agreement was observed in the LVEF. The fully automated contour detection method provided assessment of quantitative global LV function that is comparable to manual analysis, but offered the advantage of being more consistent, more reproducible, and less operator-dependent. Sievers et al. [67] investigated 100 subjects (40 normal subjects, 40 patients with ischemic cardiomyopathy, and 20 patients with nonischemic cardiomyopathy) using a 1.5-T CMR imager. LVEF was significantly underestimated by the visual reader in all 3 groups. The difference was larger in normal subjects than in patients with cardiomyopathy. The interobserver variability was smaller for the quantitative assessment than for the visual estimation. Attili et al. [69] reported that recent quantitation-oriented advances in CMR hardware and software have resulted in significant improvements in image quality and a reduction in imaging time. To conclude, the study by Holloway et al. [59] confirms that the visual CMR approach for LVEF assessment may be used for rapid assessment of LV function in clinical practice where accuracy is of less concern. For an accurate analysis of LV function, the quantitative standard short axis approach is required.