Radial Imaging Research Articles

Study of Z-pinch dynamic hohlraum shadowgraphy

In order to obtain the dynamic evolution image of tungsten array for foam padding, and to research the form of interaction between tungsten plasma and foam column, a shadow imaging system of four-frame ultraviolet probe laser (266 nm) is designed on 1 MA pulse power device. The time resolution of the system is 2.5 ns, and static space resolution is superior to 70 μm. The radial shadowgraphy image reveals the whole process from the melting and expansion of solid wire to the interaction between the precursor plasma and the foam, from the pinch to rebound inflation. The image shows the continuous interaction between tungsten plasma and foam in the form of Raining within a time of about 50 ns, the plasma shell structure is not found in the whole period of pinch. The quantitative analysis indicates that the minimum pinching speed of the foam column is 1.0×106 cm/s, and maximum pinching speed is 6.0×106 cm/s, and the axial stagnation diameter is about 1 mm. Shadowgram mainly shows the inverse bremsstrunlung effect of interaction between laser and plasma through simulation calculating, and main tungsten plasma interacting with foam column image is shown through synchronizing radial power profile.

Pretreatment Diffusion-Weighted and Dynamic Contrast-Enhanced MRI for Prediction of Local Treatment Response in Squamous Cell Carcinomas of the Head and Neck

The objective of our study was to predict response to chemoradiation therapy in patients with head and neck squamous cell carcinoma (HNSCC) by combined use of diffusion-weighted imaging (DWI) and high-spatial-resolution, high-temporal-resolution dynamic contrast-enhanced MRI (DCE-MRI) parameters from primary tumors and metastatic nodes. Thirty-two patients underwent pretreatment DWI and DCE-MRI using a modified radial imaging sequence. Postprocessing of data included motion-correction algorithms to reduce motion artifacts. The median apparent diffusion coefficient (ADC), volume transfer constant (K(trans)), extracellular extravascular volume fraction (v(e)), and plasma volume fraction (v(p)) were computed from primary tumors and nodal masses. The quality of the DCE-MRI maps was estimated using a threshold median chi-square value of 0.10 or less. Multivariate logistic regression and receiver operating characteristic curve analyses were used to determine the best model to discriminate responders from nonresponders. Acceptable χ(2) values were observed from 84% of primary tumors and 100% of nodal masses. Five patients with unsatisfactory DCE-MRI data were excluded and DCE-MRI data for three patients who died of unrelated causes were censored from analysis. The median follow-up for the remaining patients (n = 24) was 23.72 months. When ADC and DCE-MRI parameters (K(trans), v(e), v(p)) from both primary tumors and nodal masses were incorporated into multivariate logistic regression analyses, a considerably higher discriminative accuracy (area under the curve [AUC] = 0.85) with a sensitivity of 81.3% and specificity of 75% was observed in differentiating responders (n = 16) from nonresponders (n = 8). The combined use of DWI and DCE-MRI parameters from both primary tumors and nodal masses may aid in prediction of response to chemoradiation therapy in patients with HNSCC.

Contrast enhanced lung MRI in mice using ultra‐short echo time radial imaging and intratracheally administrated Gd‐DOTA‐based nanoparticles

To investigate the in vivo T1 -enhancement of the lung parenchyma in free-breathing healthy mice following intratracheal administration of Gd-DOTA-based nanoparticles, to assess the enhancement kinetics of the instilled contrast medium and to identify its elimination pathways. Ultrashort Echo Time (276 μs) proton MRI of the lung was performed (N = 14) at 4.7 T after the intratracheal instillation of 50 μL of seven different concentrations of contrast agent solution (from 2 to 100 mM of Gd(3+) ). The signal enhancement (SE) in lungs, blood, liver, kidneys, and bladder was assessed (N = 3) for a 50 mM concentration solution at different time points. The largest SE in lungs (266 ± 14%) was observed for a 50 mM solution of Gd(3+) . In lungs, the SE was observed to decay exponentially with a time constant of 149 ± 51 min. The passage of the nanoparticles from lung tissue to blood and kidneys, and ultimately to the bladder, was observed. No significant hepatic enhancement was measured. This study demonstrates the feasibility of large SEs of lung tissue using intratracheally administrated solutions of Gd-based contrast agents. In future applications, the SE in lungs could be used to image the biodistribution of coadministrated drug aerosols or to selectively enhance lung diseased tissues.

Ultrasound Biomicroscopy of the Ciliary Body in Ocular/Oculodermal Melanocytosis

To describe the ultrasound biomicroscopy (UBM) findings of the ciliary body in patients with ocular/oculodermal melanocytosis. Retrospective observational case series study. A retrospective chart and imaging database review was conducted for patients with unilateral ocular/oculodermal melanocytosis who underwent UBM examination at the Ocular Oncology Clinic of Princess Margaret Hospital. Radial images of the ciliary body at the 3-, 6-, 9-, and 12-o'clock positions were obtained in both eyes. UBM characteristics included ciliary body thickness and reflectivity. The eye with ocular/oculodermal melanocytosis was compared with the contralateral unaffected eye as a control. Statistical significance was analyzed with Student t test. Twelve patients were included. All patients showed unilateral diffuse pigmentation involving episclera and anterior chamber angle. The iris showed diffuse pigmentation in 10 cases and sectorial in 2. Mean ciliary body thickness of the affected eyes was 0.581 ± 0.058mm (range 0.489-0.744) compared with 0.475 ± 0.048mm (range 0.406-0.622) in the contralateral eye, which was found to be a statistically significant difference (P < .001). The affected ciliary body showed hyperreflectivity when compared with the unaffected eye. All affected eyes were graded as medium to high reflectivity compared with the unaffected eyes that showed a medium to medium/low reflectivity. Ciliary body involvement in ocular/oculodermal melanocytosis presents as increased thickness and higher ultrasound reflectivity on UBM when compared with the unaffected eye. UBM is helpful in imaging clinically undetectable areas of melanocytosis involving the ciliary body.

Optimized 3D ultrashort echo time pulmonary MRI

To optimize 3D radial ultrashort echo time MRI for high resolution whole-lung imaging. 3D radial ultrashort echo time was implemented on a 3T scanner to investigate the effects of: (1) limited field-of-view excitation, (2) variable density readouts, and (3) radial oversampling. Improvements in noise performance and spatial resolution were assessed through simulation and phantom studies. Their effects on lung and airway visualization in five healthy male human subjects (mean age 32 years) were compared qualitatively through blinded ordinal scoring by two cardiothoracic radiologists using a nonparametric Friedman test (P < 0.05). Relative signal difference between endobronchial air and adjacent lung tissue, normalized to nearby vessel, was used as a surrogate for lung tissue signal. Quantitative measures were compared using the paired Student's t-test (P < 0.05). Finally, clinical feasibility was investigated in a patient with interstitial fibrosis. Simulation and phantom studies showed up to 67% improvement in SNR and reduced blurring for short T2* species using all three optimizations. In vivo images showed decreased artifacts and improved lung tissue and airway visualization both qualitatively and quantitatively. The use of limited field-of-view excitation, variable readout gradients, and radial oversampling significantly improve the technical quality of 3D radial ultrashort echo time lung images.

Free-breathing dynamic contrast-enhanced MRI of the abdomen and chest using a radial gradient echo sequence with K-space weighted image contrast (KWIC)

To evaluate the feasibility of free-breathing, dynamic contrast-enhanced (DCE) MRI of the abdomen and thorax using the radial-gradient-echo sequence with k-space weighted image contrast (KWIC) reconstruction. Institutional review board approval was obtained. Fourteen patients underwent free-breathing radial DCE-MRI. Radial MRI yielded full-frame images by gridding all k-space data and time-resolved subframe images by using KWIC reconstruction technique. Using subframe KWIC images, voxel-wise perfusion maps were created. For comparison, the breath-hold conventional Cartesian 3D-gradient-echo sequence (VIBE) was also performed during the equilibrium phase. The image qualities of radial and conventional VIBE images were compared quantitatively and qualitatively. Radial DCE-MRI provided high spatial resolution (1.4 × 1.4 mm) and temporal resolution (4.1 s for subframe images) allowing voxel-wise perfusion mapping with negligible motion or streaking artefacts. There were no significant differences in SNR between full-frame radial images and conventional VIBE images (79.08 vs 74.80, P > 0.05). Overall image quality score of full-frame radial images was slightly lower than that of conventional VIBE images (3.88 ± 0.59 vs. 4.31 ± 0.97, P < 0.05), but provided clinically useful images. The free-breathing radial DCE-MRI can provide high spatial and temporal resolution while maintaining reasonably high image quality and thus is a feasible technique for DCE-MRI in the abdomen and thorax. • Dynamic contrast-enhanced magnetic resonance imaging (DCE) MRI is important in oncological imaging • Radial MRI with k-space weighted image contrast (KWIC) reconstruction offers potential improvements • Radial DCE-MRI provides good image quality, reduced artefacts and high spatial/temporal resolution.

The design and fabrication of a linear array for three-dimensional intravascular ultrasound

Current intravascular ultrasound catheters generate high resolution cross-sectional images of arterial walls. However, the elevational resolution, in the direction of the catheter, is limited, introducing image distortion. To overcome this limitation, we designed and fabricated a linear array which can be rotated to image a three-dimensional volume at each pullback position. The array consists of eight rectangular piezo-electric elements of 350 µm by 100 µm operating at a center frequency of 21 MHz with a fractional bandwidth of 80 %, separated by a kerf of 100 µm. The array has been tested on both an ex vivo bovine artery and phantoms and, using the real aperture of the array, axially densely sampled images of the artery are obtained in every position. The array consistently yields significantly higher resolution in longitudinal images and more detail in radial images compared to a conventional catheter.

Handheld Imaging System for Contactless Tri-Modal Biometric Identification

Fingerprinting is the most widely used form of biometric identification because large databases are already available and law enforcement agencies have decades of experience with this technology. In addition, many fingerprinting units on the market are small in size, low power, and inexpensive. Common deficiencies carried by current fingerprinting technologies are distortions introduced when the finger touches the surface of the reader. The current study describes the development of a novel, handheld, contactless fingerprinting system which is capable of acquiring individual fingers with 180 degree view (first modality). Liveliness is examined by transmitted Infra-Red (IR) light (second modality), which allows the viewing of blood vessel networks and four-slap images and palm prints (third modality). This system is able to produce fingerprint images which are approximately 99% accurate representations of a finger's surface. This was verified by exam- ining a NIST certified aluminum test sample. As demonstrated in our study, this is compared to an average of 15% distortion of the distances between a finger's ridges when imaged with contact based systems. Our radial line-scan imaging allows for nail-to-nail acquisition of an individual fingerprint, where the format of the recorded image is analogous to an ink-rolled fingerprint. The system will securely and wirelessly transfers fingerprint images to any law enforcement center via built-in Wi-Fi connection.

Myocardial perfusion MRI with an undersampled 3D stack‐of‐stars sequence

To determine the feasibility of three-dimensional (3D) hybrid radial (stack-of-stars) MRI with spatiotemporal total variation (TV) constrained reconstruction for dynamic contrast enhanced myocardial perfusion imaging. An ECG-triggered saturation recovery turboFLASH sequence with undersampled stack-of-stars sampling with spatiotemporal TV constrained reconstruction was developed for dynamic contrast enhanced myocardial perfusion imaging. Simulations were performed to study the dependence of the approach to steady state on flip angle and saturation recovery time for this stack-of-stars acquisition. Phantom studies were used to show the effect of the flip angle selection and imperfect spoiling on image qualities. Studies were done in three humans to test the feasibility of the approach for myocardial perfusion imaging. The simulation and phantom studies showed that imperfect spoiling and magnetization changes during the readout were a function of flip angle and nonoptimized selection of flip angle could degrade the images. Low flip angle acquisitions in the human subjects result in images with good quality similar to multislice radial 2D images. 3D stack-of-stars sampling with spatiotemporal TV constrained reconstruction provides a promising alternative for myocardial perfusion imaging.

Reconstruction of undersampled radial PatLoc imaging using total generalized variation

In the case of radial imaging with nonlinear spatial encoding fields, a prominent star-shaped artifact has been observed if a spin distribution is encoded with an undersampled trajectory. This work presents a new iterative reconstruction method based on the total generalized variation, which reduces this artifact. For this approach, a sampling operator (as well as its adjoint) is needed that maps data from PatLoc k-space to the final image space. It is shown that this can be realized as a type-3 nonuniform fast Fourier transform, which is implemented by a combination of a type-1 and type-2 nonuniform fast Fourier transform. Using this operator, it is also possible to implement an iterative conjugate gradient SENSE based method for PatLoc reconstruction, which leads to a significant reduction of computation time in comparison to conventional PatLoc image reconstruction methods. Results from numerical simulations and in vivo PatLoc measurements with as few as 16 radial projections are presented, which demonstrate significant improvements in image quality with the total generalized variation-based approach.

Study on the Optimum Pulse-Taking Pressure and Probe Film Material Parameters during the Pulse Image Condition Detection

Pulse image detecting device was applied to acquire radial dynamic pulse images. In this paper, we improved the probe structure of the pulse image detecting device with new film material. Four kinds of different thickness films, the different pulse-taking pressures and the different sealed chamber pressures were used to determine the optimum film. For different subjects, the pulse amplitude was extracted with the different pulse-taking pressures and different sealed cavity pressures. The experiment results had shown that the best pulse amplitude could be obtained with the film thickness for 0.504 mm, pulse-taking pressure for 3 N and the sealed cavity pressure for 120KPa. This work provided an important theoretical basis for the parameter choice of the pulse image detection device.

Image stitching and image reconstruction of intestines captured using radial imaging capsule endoscope

This study investigates image processing using the radial imaging capsule endoscope (RICE) system. First, an experimental environment is established in which a simulated object has a shape that is similar to a cylinder, such that a triaxial platform can be used to push the RICE into the sample and capture radial images. Then four algorithms (mean absolute error, mean square error, Pearson correlation coefficient, and deformation processing) are used to stitch the images together. The Pearson correlation coefficient method is the most effective algorithm because it yields the highest peak signal-to-noise ratio, higher than 80.69 compared to the original image. Furthermore, a living animal experiment is carried out. Finally, the Pearson correlation coefficient method and vector deformation processing are used to stitch the images that were captured in the living animal experiment. This method is very attractive because unlike the other methods, in which two lenses are required to reconstruct the geometrical image, RICE uses only one lens and one mirror.

Flow-gated radial phase-contrast imaging in the presence of weak flow

To implement a flow-gating method to acquire phase-contrast (PC) images of carotid arteries without use of an electrocardiography (ECG) signal to synchronize the acquisition of imaging data with pulsatile arterial flow. The flow-gating method was realized through radial scanning and sophisticated post-processing methods including downsampling, complex difference, and correlation analysis to improve the evaluation of flow-gating times in radial phase-contrast scans. Quantitatively comparable results (R=0.92-0.96, n=9) of flow-related parameters, including mean velocity, mean flow rate, and flow volume, with conventional ECG-gated imaging demonstrated that the proposed method is highly feasible. The radial flow-gating PC imaging method is applicable in carotid arteries. The proposed flow-gating method can potentially avoid the setting up of ECG-related equipment for brain imaging. This technique has potential use in patients with arrhythmia or weak ECG signals.

Abstract 548: Variations in Venous Wall Strain Can Be Modeled and Measured Using IVUS-Derived Elastography

Objectives: Iliofemoral venous outflow stenting has been used to treat both acute and chronic venous thrombosis. It may be beneficial to understand the properties of the normal venous wall and the flow through collapsible tubes to develop new stent technology and improve long-term patency. We hypothesize that radial and circumferential strain can be modeled and measured using intravascular ultrasound (IVUS) techniques to describe venous geometry and asymmetric vessel wall characteristics. Methods: A hydrogel phantom was used to mimic the mechanical properties of a homogeneous vein, including geometry and wall compliance. Radio-frequency (RF) echo frames were acquired using a modified IVUS system with an 8.5 Mhz catheter. All RF signals were digitized to 14 bits at 50 MHz. Radial strain was estimated by applying an intensity matching, image registration based algorithm to the digitized frames. Results: The radial strain images (Figure 1) show increasing positive strain (radial wall thickening) on the top and bottom of the phantom with decreasing negative values (radial wall thinning) at either side. Results suggest an asymmetric compression pattern typical of a vessel collapsing under negative pressure. Conclusions: In conclusion, our data suggest that novel strain analysis can be performed on a phantom vessel consistent with the mechanical properties of the venous system. Further work with venous elastography will help define the mechanical properties of the venous wall and facilitate the development of new stent technology to treat venous disease.

Performance of sampling density‐weighted and postfiltered density‐adapted projection reconstruction in sodium magnetic resonance imaging

Sampling density-weighted apodization projection reconstruction sequences are evaluated for three-dimensional radial imaging. The readout gradients of the sampling density-weighted apodization sequence are designed such that the locally averaged sampling density matches a Hamming filter function. This technique is compared with density-adapted projection reconstruction with nonfiltered and postfiltered image reconstruction. Sampling density-weighted apodization theoretically allows for a 1.28-fold higher signal-to-noise ratio compared with postfiltered density-adapted projection reconstruction sequences, if T(2)* decay is negligible compared with the readout duration T(RO). Simulations of the point-spread functions are performed for monoexponential and biexponential decay to investigate the effects of T(2)* decay on the performance of the different sequences. Postfiltered density-adapted projection reconstruction performs superior to sampling density-weighted apodization for large T(RO)/T(2)* ratios [>1.36 (monoexponential decay); >0.35 (biexponential decay with T(2s)*/T(2f)* = 10)], if signal-to-noise ratio of point-like objects is considered. In conclusion, it depends on the readout parameters, the T(2)* relaxation times, and the dimensions of the subject which of both sequences is most suitable.

Targeted Left Ventricular Lead Placement to Guide Cardiac Resynchronization Therapy: The TARGET Study: A Randomized, Controlled Trial

This study sought to assess the impact of targeted left ventricular (LV) lead placement on outcomes of cardiac resynchronization therapy (CRT). Placement of the LV lead to the latest sites of contraction and away from the scar confers the best response to CRT. We conducted a randomized, controlled trial to compare a targeted approach to LV lead placement with usual care. A total of 220 patients scheduled for CRT underwent baseline echocardiographic speckle-tracking 2-dimensional radial strain imaging and were then randomized 1:1 into 2 groups. In group 1 (TARGET [Targeted Left Ventricular Lead Placement to Guide Cardiac Resynchronization Therapy]), the LV lead was positioned at the latest site of peak contraction with an amplitude of >10% to signify freedom from scar. In group 2 (control) patients underwent standard unguided CRT. Patients were classified by the relationship of the LV lead to the optimal site as concordant (at optimal site), adjacent (within 1 segment), or remote (≥2 segments away). The primary endpoint was a ≥15% reduction in LV end-systolic volume at 6 months. Secondary endpoints were clinical response (≥1 improvement in New York Heart Association functional class), all-cause mortality, and combined all-cause mortality and heart failure-related hospitalization. The groups were balanced at randomization. In the TARGET group, there was a greater proportion of responders at 6 months (70% vs. 55%, p = 0.031), giving an absolute difference in the primary endpoint of 15% (95% confidence interval: 2% to 28%). Compared with controls, TARGET patients had a higher clinical response (83% vs. 65%, p = 0.003) and lower rates of the combined endpoint (log-rank test, p = 0.031). Compared with standard CRT treatment, the use of speckle-tracking echocardiography to the target LV lead placement yields significantly improved response and clinical status and lower rates of combined death and heart failure-related hospitalization. (Targeted Left Ventricular Lead Placement to Guide Cardiac Resynchronization Therapy [TARGET] study); ISRCTN19717943).

Compressed sensing reconstruction for whole‐heart imaging with 3D radial trajectories: A graphics processing unit implementation

A disadvantage of three-dimensional (3D) isotropic acquisition in whole-heart coronary MRI is the prolonged data acquisition time. Isotropic 3D radial trajectories allow undersampling of k-space data in all three spatial dimensions, enabling accelerated acquisition of the volumetric data. Compressed sensing (CS) reconstruction can provide further acceleration in the acquisition by removing the incoherent artifacts due to undersampling and improving the image quality. However, the heavy computational overhead of the CS reconstruction has been a limiting factor for its application. In this article, a parallelized implementation of an iterative CS reconstruction method for 3D radial acquisitions using a commercial graphics processing unit is presented. The execution time of the graphics processing unit-implemented CS reconstruction was compared with that of the C++ implementation, and the efficacy of the undersampled 3D radial acquisition with CS reconstruction was investigated in both phantom and whole-heart coronary data sets. Subsequently, the efficacy of CS in suppressing streaking artifacts in 3D whole-heart coronary MRI with 3D radial imaging and its convergence properties were studied. The CS reconstruction provides improved image quality (in terms of vessel sharpness and suppression of noise-like artifacts) compared with the conventional 3D gridding algorithm, and the graphics processing unit implementation greatly reduces the execution time of CS reconstruction yielding 34-54 times speed-up compared with C++ implementation.

Improved accelerated breath-hold radial cine image reconstruction by acquiring additional free-breathing data between breath-holds

Background Evaluation of cardiac function is clinically performed using multi-slice breath-hold (BH) acquisition, in which patient breathes for a period of 40-60 seconds between a BH of 10-12 seconds. This results in suboptimal data acquisition efficiency. In this study, we propose to take advantage of the time between multiple BHs to acquire additional free-breathing (FB) data that can be used in the reconstruction of undersampled BH acquisition without increasing the total scan time.

Compression2: compressed sensing with compressed coil arrays

Summary Compressed sensing with PCA based coil compression is a promising way to obtain high quality radial perfusion images without incurring the high computation cost and memory requirements associated with large multi-coil arrays Background Imaging with large coil arrays is desirable for rapid imaging and high signal to noise ratio. Compressed sensing (CS) is a promising way to accelerate myocardial perfusion imaging [1]. However with increasing number of coils CS is costly in terms of memory and computation time. Coil compression methods for reconstructing cardiac cine data with parallel imaging have been proposed [2,3]. Unlike previous methods, here we employ a coil compression method with a CS reconstruction combined with a coil-based streak suppression method. The approach is tested on undersampled radial myocardial perfusion data. Methods

Real‐time magnetic resonance imaging of normal swallowing

To evaluate the use of a novel real-time magnetic resonance imaging (MRI) technique for the assessment of normal swallowing dynamics. In a cohort of 10 healthy subjects, real-time MRI movies at 24.3 frames per second were obtained in sagittal, coronal, and axial orientation during self-controlled swallows of 5 mL pineapple juice as oral contrast bolus. All studies were performed with the use of a commercial MRI system at 3 T combining two sets of radiofrequency receiver coils. Real-time movies relied on a fast low-angle shot (FLASH) MRI sequence with radial undersampling and image reconstruction by nonlinear inversion yielding 41.23 msec acquisition time for an in-plane resolution of 1.5 mm. Evaluations focused on clinical image quality as well as visualization and temporal quantification of distinct swallowing functions. Throughout the entire process, the swallowing dynamics were well depicted and characterized with almost no visible image artifacts in all subjects. The mid-sagittal plane turned out to be most valuable. The movies allowed for a quantitative determination of the temporal pattern of all swallowing events. The proposed real-time MRI technique yields noninvasive, robust, and quantitative access to the physiology of normal swallowing in healthy subjects at high temporal resolution and image quality.