Conventional Keyhole Research Articles

The Improved Antigen Uptake and Presentation of Dendritic Cells Using Cell-Penetrating D-octaarginine-Linked PNVA-co-AA as a Novel Dendritic Cell-Based Vaccine.

Cancer immunotherapy using antigen-pulsed dendritic cells can induce strong cellular immune responses by priming cytotoxic T lymphocytes. In this study, we pulsed tumor cell lysates with VP-R8, a cell-penetrating D-octaarginine-linked co-polymer of N-vinylacetamide and acrylic acid (PNVA-co-AA), into the DC2.4 murine dendritic cell line to improve antigen uptake and then determined the anti-tumor effect in tumor-bearing mice. DC2.4 cells were pulsed with the cell lysate of EL4, a murine lymphoma cell line, and VP-R8 to generate the DC2.4 vaccine. For the in vivo study, DC2.4 cells pulsed with EL4 lysate and VP-R8 were subcutaneously injected into the inguinal lymph node to investigate the anti-tumor effect against EL4 and EL4-specific T cell immune responses. VP-R8 significantly improved antigen uptake into DC2.4 compared to conventional keyhole limpet hemocyanin (p < 0.05). The expression of MHC class I, MHC class II, and CD86 in DC2.4 cells significantly increased after pulsing tumor lysates with VP-R8 compared to other treatments (p < 0.05). The intra-lymph node injection of DC2.4 pulsed with both VP-R8 and EL4 lysate significantly decreased tumor growth compared to DC2.4 pulsed with KLH and lysates (p < 0.05) and induced tumor-infiltrating CD8T cells. The DC2.4 vaccine also remarkably increased the population of IFN-gamma-producing T cells and CTL activity against EL4 cells. In conclusion, we demonstrated that VP-R8 markedly enhances the efficiency of dendritic cell-based vaccines in priming robust anti-tumor immunity, suggesting its potential as a beneficial additive for dendritic cell-based immunotherapy.

Robotic surgery in gynaecology: Scientific Impact Paper No. 71 (July 2022).

The use of robotic-assisted keyhole surgery in gynaecology has expanded in recent years owing to technical advances. These include 3D viewing leading to improved depth perception, limitation of tremor, potential for greater precision and discrimination of tissues, a shorter learning curve and improved comfort for surgeons compared with conventional keyhole and open abdominal surgery. Robotic-assisted keyhole surgery, compared with conventional keyhole surgery, improves surgical performance without increasing operating time, minimises blood loss and intra- or postoperative complications, while reducing the need to revert to abdominal surgery. Moreover, surgeons using a robot experience fewer skeletomuscular problems of their own in the short and long term than those operating without a robot as an additional tool. This Scientific Impact Paper looks at the use of a robot in different fields of gynaecological surgery. A robot could be considered safe and a more effective surgical tool than conventional keyhole surgery for women who have to undergo complex gynaecology surgery or have associated medical issues such as body-mass index (BMI) at 30 kg/m2 or above or lung problems. The introduction of the use of robots in keyhole surgery has resulted in a decrease in the number of traditional open surgeries and the risk of conversion to open surgery after traditional keyhole surgery; both of which should be considered when examining the cost-benefit of using a robot. Limitations of robotic-assisted surgery remain the associated higher costs. In womb cancer surgery there is good evidence that introducing robotics into the service improves outcomes for women and may reduce costs.

Technical Note: Real-time 3D MRI in the presence of motion for MRI-guided radiotherapy: 3D Dynamic keyhole imaging with super-resolution.

The purpose of this study was to present real-time three-dimensional (3D) magnetic resonance imaging (MRI) in the presence of motion for MRI-guided radiotherapy (MRgRT) using dynamic keyhole imaging for high-temporal acquisition and super-resolution generative (SRG) model for high-spatial reconstruction. We propose a unique real-time 3D MRI technique by combining a data sharing technique (3D dynamic keyhole imaging) with a SRG model using cascaded deep learning technique. 3D dynamic keyhole imaging utilizes the data sharing mechanism by combining keyhole central k-space data acquired in real-time with high-spatial, high-temporal resolution prior peripheral k-space data at various motion positions prepared by the SRG model. The efficacy of the 3D dynamic keyhole imaging with super-resolution (SR_dKeyhole) was compared to the ground-truth super-resolution images with the original full k-space data. It was also compared with the zero-filling reconstruction (zero-filling), conventional keyhole reconstruction with low-spatial high-temporal prior data (LR_cKeyhole), and conventional keyhole reconstruction with super-resolution prior data (SR_cKeyhole). High-spatial, high-temporal resolution 3D MRI datasets (1.5×1.5×6mm3 ) were generated from low-spatial, high-temporal resolution 3D MRI datasets (6×6×6mm3 ) using the cascaded deep learning SRG framework (<100ms/volume). 3D dynamic keyhole imaging with the SRG model provided high-spatial, high-temporal resolution images (1.5×1.5×6mm3 , 455ms) with the highest similarity to the ground-truth SR images without any noticeable artifacts. Structural similarity indices (SSIM) of the reconstructed 3D MRI to the original SR 3D MRI were 0.65, 0.66, 0.86, and 0.89 for zero-filling, LR_cKeyhole, SR_cKeyhole, and SR_dKeyhole, respectively (1 for identical image). In addition, average value of image relative error (IRE) of the reconstructed 3D MRI to the original SR 3D MRI were 0.169, 0.191, 0.079, and 0.067 for zero-filling, LR_cKeyhole, SR_cKeyhole, and SR_dKeyhole, respectively (0 for identical image). We demonstrated that high-spatial, high-temporal resolution 3D MRI was feasible by combing 3D dynamic keyhole imaging with a SRG model in terms of image quality and imaging time. The proposed technique can be utilized for real-time 3D MRgRT.

Modified friction stir clinching with protuberance-keyhole levelling: A process for production of welds with high strength

Modified friction stir clinching (MFSC) with protuberance-keyhole leveling approach is employed in joining dissimilar AA2024-T3/AA7075-T6 Al alloys. This technique is a two-step approach where friction stir clinching is established in the first step while the inherent step-like (protuberance-keyhole cavity) is eliminated in the second step. The microstructure, mechanical properties and fracture mode of the MFSC joints are examined and compared with that of the conventional keyhole friction stir spot welds. The results reveal that the new approach eliminates the formation of hook defect while geometric-differential flow-induced defects are formed in the joint. Protuberance and shoulder indentation refilling processes form flow-induced defects at the weld center and at the circumferential shoulder edges respectively. The severity of these defects is reduced via better inter-mixing and flowability at high tool rotational speed. Atomic diffusion induces the formation of Al2CuMg and Mg2Si phases in the joints (stir zones). A rise in tool rotational speed increases the tensile-shear and cross-tension loads of the joint from 6798 N to 9487 N and 4366 N to 6850 N respectively. The new joining process improved the joint quality due to enhanced effective bonded/shear area as compared to that of the conventional keyhole friction stir spot welded joint.

Process Stability during Laser Beam Welding with Beam Oscillation and Wire Feed

Beam oscillation in laser material processing makes it possible to influence process behavior in terms of energy distribution, stability, melt pool dynamics and solidification. Within the setup presented here, the beam is oscillated transverse to the welding direction, and the filler wire is fed to the melt pool of a butt joint with an air gap. One advantage of this setup is the large gap bridging ability. Certain parameter sets lead to the so-called buttonhole welding method, which allows laser welding of smooth and nearly ripple-free seams. Observations showed a transition area between conventional keyhole and buttonhole welding in which the process is destabilized. Welds made with parameter sets from this area contain critical seam defects. Welding experiments with high-speed video recording and a simplified analytical model about the wire-beam interaction have helped to elucidate the mechanisms behind this. EN AW-6082 sheet material in 1.5 mm thickness and ML 4043 filler wire with 1.2 mm diameter were used. The investigations lead to the conclusion that partially melted wire segments result at certain parameter relations which hinder the formation of a buttonhole. If these segments are prevented, buttonhole welding occurs. In the transition area, these segments are very small and can lead to the detachment of a buttonhole, resulting in the named seam defects.

Quantitative contrast study of sellar region by lateral orbital keyhole approach and conventional keyhole approach

Objective To compare lateral orbital keyhole approach(LOK) with conventional keyhole approach including supraorbital keyhole approach (SOK) and pterional approach(PTK) for exposuring the sellar region and operation ability, to provide theoretical and practical basis for the clinic. Methods From January, 2017 to Feburary, 2018, 15 cadaver head specimens of Chinese (30 sides) fixed by formalin were randomly divided into 3 groups, simulating SOK, LOK and PTK, application of frameless neuronavigation system, intersection of the posterior margin of the optic chiasma and the lamina terminalis served as the base point. Six different reference points were selected to radiate into the parasellar region of the skull base. The direction of the 2 adjacent reference points were connected to the base point to form a triangle. Six triangles constituted the sellar region to represent the total area. The supratentorial area, ipsilateral area, inferior area and contralateral area were calculated by stacking triangle. The comparison was made between groups. The Salma operation exposure scale was used to simulate the aneurysms of the common parts in the brain and the quantitative scores were performed. Results The total parasellar regions by SOK, LOK and PTK respectively were: (1641.6±295.6) mm2, (1782.3±294.6) mm2 and (1552.5±307.4) mm2. There was no statistical difference(P>0.05); To compare the supratentorial region, SOK and LOK were both bigger than PTK(P<0.05); To compare the ipsilateral and infratentorial area, LOK and PTK were both bigger than SOK respectively(P<0.05); To compare the contralateral area, SOK, LOK and PTK were increased in turn(P<0.05). Salma operation exposure scale was used to get the scores: the score of SOK was 29.7 (39.08%), LOK was 37.0 (48.68%), and PTK was 36.1 (47.50%). Conclusion Anatomical analysis displayed that the 3 keyhole approaches showed different exposure of each part the parasellar regions, the LOK had a good exposure to the parasellar region and so as the higher maneuverability. But the clinical application should be comprehensive analysis, pay attention to specific lesions and make an appropriate choice. It has important clinical significance to improve the prognosis of patients. Key words: Sellar region; Keyhole approach; Applied anatomy; Quantificative study

TH‐EF‐BRA‐05: A Method of Near Real‐Time 4D MRI Using Volumetric Dynamic Keyhole (VDK) in the Presence of Respiratory Motion for MR‐Guided Radiotherapy

Purpose:To develop a novel method that enables 4D MR imaging in near real‐time for continuous monitoring of tumor motion in MR‐guided radiotherapy.Methods:This method is mainly based on an idea of expanding dynamic keyhole to full volumetric imaging acquisition. In the VDK approach introduced in this study, a library of peripheral volumetric k‐space data is generated in given number of phases (5 and 10 in this study) in advance. For 4D MRI at any given time, only volumetric central k‐space data are acquired in real‐time and combined with pre‐acquired peripheral volumetric k‐space data in the library corresponding to the respiratory phase (or amplitude). The combined k‐space data are Fourier‐transformed to MR images. For simulation study, an MRXCAT program was used to generate synthetic MR images of the thorax with desired respiratory motion, contrast levels, and spatial and temporal resolution. 20 phases of volumetric MR images, with 200 ms temporal resolution in 4 s respiratory period, were generated using balanced steady‐state free precession MR pulse sequence. The total acquisition time was 21.5s/phase with a voxel size of 3×3×5 mm3 and an image matrix of 128×128×56. Image similarity was evaluated with difference maps between the reference and reconstructed images. The VDK, conventional keyhole, and zero filling methods were compared for this simulation study.Results:Using 80% of the ky data and 70% of the kz data from the library resulted in 12.20% average intensity difference from the reference, and 21.60% and 28.45% difference in threshold pixel difference for conventional keyhole and zero filling, respectively. The imaging time will be reduced from 21.5s to 1.3s per volume using the VDK method.Conclusion:Near real‐time 4D MR imaging can be achieved using the volumetric dynamic keyhole method. That makes the possibility of utilizing 4D MRI during MR‐guided radiotherapy.

Quantifying the accuracy of the tumor motion and area as a function of acceleration factor for the simulation of the dynamic keyhole magnetic resonance imaging method.

The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging. To date, this method has not been investigated with cancer patient magnetic resonance imaging (MRI) data. The goal of this study was to assess the dynamic keyhole method for the task of lung tumor localization using cine-MR images reconstructed in the presence of respiratory motion. The dynamic keyhole method utilizes a previously acquired a library of peripheral k-space datasets at similar displacement and phase (where phase is simply used to determine whether the breathing is inhale to exhale or exhale to inhale) respiratory bins in conjunction with central k-space datasets (keyhole) acquired. External respiratory signals drive the process of sorting, matching, and combining the two k-space streams for each respiratory bin, thereby achieving faster image acquisition without substantial motion artifacts. This study was the first that investigates the impact of k-space undersampling on lung tumor motion and area assessment across clinically available techniques (zero-filling and conventional keyhole). In this study, the dynamic keyhole, conventional keyhole and zero-filling methods were compared to full k-space dataset acquisition by quantifying (1) the keyhole size required for central k-space datasets for constant image quality across sixty four cine-MRI datasets from nine lung cancer patients, (2) the intensity difference between the original and reconstructed images in a constant keyhole size, and (3) the accuracy of tumor motion and area directly measured by tumor autocontouring. For constant image quality, the dynamic keyhole method, conventional keyhole, and zero-filling methods required 22%, 34%, and 49% of the keyhole size (P < 0.0001), respectively, compared to the full k-space image acquisition method. Compared to the conventional keyhole and zero-filling reconstructed images with the keyhole size utilized in the dynamic keyhole method, an average intensity difference of the dynamic keyhole reconstructed images (P < 0.0001) was minimal, and resulted in the accuracy of tumor motion within 99.6% (P < 0.0001) and the accuracy of tumor area within 98.0% (P < 0.0001) for lung tumor monitoring applications. This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiation therapy requiring the MR monitoring of thoracic tumors. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by up to a factor of five compared with full k-space methods for real-time lung tumor MRI.

Dynamic keyhole: a novel method to improve MR images in the presence of respiratory motion for real-time MRI.

In this work, the authors present a novel magnetic resonance imaging reconstruction method to improve the quality of MR images in the presence of respiratory motion for real-time thoracic image-guided radiotherapy. This new reconstruction method is called dynamic keyhole and utilizes a library of previously acquired, peripheral k-space datasets from the same (or similar) respiratory state in conjunction with central k-space datasets acquired in real-time. Internal or external respiratory signals are utilized to sort, match, and combine the two separate peripheral and central k-space datasets with respect to respiratory displacement, thereby reducing acquisition time and improving image quality without respiratory-related artifacts. In this study, the dynamic keyhole, conventional keyhole, and zero-filling methods were compared to full k-space acquisition (ground truth) for 60 coronal datasets acquired from 15 healthy human subjects. For the same image-quality difference from the ground-truth image, the dynamic keyhole method reused 79% of the prior peripheral phase-encoding lines, while the conventional keyhole reused 73% and zero-filling 63% (p-value < 0.0001), corresponding to faster acquisition speed of dynamic keyhole for real-time imaging applications. This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiotherapy requiring real-time MR monitoring of the thoracic region. Based on the results from this study, the dynamic keyhole method could increase the temporal resolution by a factor of five compared with full k-space methods.

WE‐G‐18C‐08: Real Time Tumor Imaging Using a Novel Dynamic Keyhole MRI Reconstruction Technique

Purpose:To test the hypothesis that the novel Dynamic Keyhole MRI reconstruction technique can accelerate image acquisition whilst maintaining high image quality for lung cancer patients.Methods:18 MRI datasets from 5 lung cancer patients were acquired using a 3T MRI scanner. These datasets were retrospectively reconstructed using (A) The novel Dynamic Keyhole technique, (B) The conventional keyhole technique and (C) the conventional zero filling technique. The dynamic keyhole technique in MRI refers to techniques in which previously acquired k‐space data is used to supplement under sampled data obtained in real time. The novel Dynamic Keyhole technique utilizes a previously acquired a library of kspace datasets in conjunction with central k‐space datasets acquired in realtime. A simultaneously acquired respiratory signal is utilized to sort, match and combine the two k‐space streams with respect to respiratory displacement. Reconstruction performance was quantified by (1) comparing the keyhole size (which corresponds to imaging speed) required to achieve the same image quality, and (2) maintaining a constant keyhole size across the three reconstruction methods to compare the resulting image quality to the ground truth image.Results:(1) The dynamic keyhole method required a mean keyhole size which was 48% smaller than the conventional keyhole technique and 60% smaller than the zero filling technique to achieve the same image quality. This directly corresponds to faster imaging. (2) When a constant keyhole size was utilized, the Dynamic Keyhole technique resulted in the smallest difference of the tumor region compared to the ground truth.Conclusion:The dynamic keyhole is a simple and adaptable technique for clinical applications requiring real‐time imaging and tumor monitoring such as MRI guided radiotherapy. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by a factor of five compared with full k‐space methods.

Laser Beam Welding of Brass

Abstract Up to date the evaporation process in laser beam welding of alloys with volatile elements is not completely understood. This paper discusses the phenomena occurring at the welding process of brass with 37m% zinc. Since copper has a solidification temperature of 1,087 °C and zinc vaporizes at a temperature of 907 °C, a strong evaporation takes place and anelongation of the keyhole can be observed. Depending upon welding velocity, the ratio of keyhole length to width is between one and six. Furthermore it is observed that a defect free weld seam is formed. Since the melt pool does not leak also for high ratios of keyhole length to width, the conventional keyhole model with a dynamic flow around the laser beam has to be adapted to a model in which the melt flow at the side of the capillary is stabilized also outside of the interaction zone of the laser beam with the melt due to strong evaporation at the flank of the keyhole.

Acceleration of conventional data acquisition in dynamic contrast enhancement: comparing keyhole approaches with compressive sensing.

Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) has become a valuable clinical tool for cancer diagnosis and prognosis. DCE MRI provides pharmacokinetic parameters dependent on the extravasation of small molecular contrast agents, and thus high temporal resolution and/or spatial resolution is required for accurate estimation of parameters. In this article we investigate the efficacy of 2 undersampling approaches to speed up DCE MRI: a conventional keyhole approach and compressed sensing-based imaging. Data reconstructed from variants of these methods has been compared with the full k-space reconstruction with respect to data quality and pharmacokinetic parameters Ktrans and ve. Overall, compressive sensing provides better data quality and reproducible parametric maps than key-hole methods with higher acceleration factors. In particular, an undersampling mask based on a priori precontrast data showed high fidelity of reconstructed data and parametric maps up to 5× acceleration.

WE-G-217A-03: Respiratory-Related External/Internal Motion Based MR Image Reconstruction Using Dynamic Keyhole for Real-Time Tumor Monitoring.

It is aim to test the hypothesis that a dynamic keyhole MRI reconstruction technique using external/internal respiratory surrogate position reduces acquisition time while retaining image quality for real-time tumor monitoring, compared to the conventional keyhole technique. 46 thoracic MRI studies with 13 healthy human subjects have been acquired using a 3T GE MRI. Acquired MR images were reconstructed using zero-filling, conventional keyhole and the proposed respiratory motion based dynamic keyhole techniques; resultant images were then compared for image quality. Undersampled k-space rate in the phase encoding direction was determined based on the difference between the original image and the reconstructed image. The position of abdominal muscles and diaphragm were used to determine any excess data that exists in the overlaid temporal data. In addition, the feasibility of the dynamic keyhole method was applied using lung tumor MR images. The result from dynamic keyhole using respiratory motion demonstrated significant improvement compared with the zero-filling and conventional keyhole methods. Firstly, the dynamic keyhole method using external respiratory motion had an overlaid average of 79.7% (204 lines) of 256 lines from 46 datasets, compared to 63.9% in zero-filling and 74.3% in conventional keyhole. Secondly, dynamic keyhole method using internal diaphragm motion had an overlaid average of 84.5% (216 lines) of 256 lines from all datasets compared to 67.1% and 77.8% or zero-filling and conventional keyhole, respectively. Lastly, dynamic keyhole has been validated with one dataset involving lung tumor MR images. Image blurring artifacts and inferior resolution were not present in the final MR images using dynamic keyhole. Dynamic keyhole method using respiratory external/internal surrogate motion has been proposed to reconstruct MR images without image artifacts and with superior resolution. This method is applicable to MR images targeting lungs and other organs affected by respiratory motion for real-time tumor motion monitoring.

Adaptive keyhole methods for dynamic magnetic resonance image reconstruction

Dynamic magnetic resonance imaging (MRI) acquires a sequence of images for the visualization of the temporal variation of tissue or organs. Keyhole methods such as Fourier keyhole (FK) and keyhole SVD (KSVD) are the most popular methods for image reconstruction in dynamic MRI. This paper provides a class of adaptive keyhole methods, called adaptive FK (AFK) and adaptive KSVD (AKSVD), for dynamic MRI reconstruction. The proposed methods are based on the conventional Fourier encoding and SVD encoding schemes. Instead of the conventional keyhole methods’ duplication of un-acquired data from the reference images, the proposed methods use a temporal model to depict the inter-frame dynamic changes and to estimate the un-acquired data in each successive frame. Because the model is online identified from the acquired data, the proposed methods do not require the pre-imaging process, the navigator signals, and any prior knowledge of the imaged objects. Furthermore, the new methods use the conventional keyhole encoding schemes without the bias to any particular object characters, and the temporal model for updating information is in the general form of AR process without the preference to any particular motion types. Hence, the proposed methods are designed as a generic approach to dynamic MRI, other than for any specific class of objects. Studies on dynamic MRI data set show that the new methods can produce images with much lower reconstruction error than the conventional FK and KSVD.

Accelerating cine phase‐contrast flow measurements using k‐t BLAST and k‐t SENSE

Conventional phase-contrast velocity mapping in the ascending aorta was combined with k-t BLAST and k-t SENSE. Up to 5.3-fold net acceleration was achieved, enabling single breath-hold acquisitions. A standard phase-contrast (PC) sequence with interleaved acquisition of the velocity-encoded segments was modified to collect data in 2 stages, a high-resolution under sampled and a low-resolution fully sampled training stage. In addition, a modification of the k-t reconstruction strategy was tested. This strategy, denoted as "plug-in," incorporates data acquired in the training stage into the final reconstruction for improved data consistency, similar to conventional keyhole. "k-t SENSE plug-in" was found to provide best image quality and most accurate flow quantification. For this strategy, at least 10 training profiles are required to yield accurate stroke volumes (relative deviation <5%) and good image quality. In vivo 2D cine velocity mapping was performed in 6 healthy volunteers with 30-32 cardiac phases (spatial resolution 1.3 x 1.3 x 8-10 mm(3), temporal resolution of 18-38 ms), yielding relative stroke volumes of 106 +/- 18% (mean +/- 2*SD) and 112 +/- 15% for 3.8 x and 5.3 x net accelerations, respectively. In summary, k-t BLAST and k-t SENSE are promising approaches that permit significant scan-time reduction in PC velocity mapping, thus making high-resolution breath-held flow quantification possible.

Laser penetration spike welding: A microlaser welding technique enabling novel product designs and constructions

A novel method for laser penetration microspot welding of sheet metal is presented. With this so called “laser spike-welding,” large gap tolerances are allowed. Depending on the ratio of laser spot radius to top plate thickness, gaps of 100% of the top layer thickness and more can be bridged. With conventional keyhole penetration welding this is only 20%–40% at most. So, with spike welding the gap between the metal plates can be increased by a factor of 2.5–5. In this way a powerful and attractive welding technique for joining of thin metal plates is available. The laser spike weld method can handle larger production tolerances and will enable novel and cheap product designs and welding of dissimilar materials.

Improved device definition in interventional magnetic resonance imaging using a rotated stripes keyhole acquisition

Keyhole acquisition techniques have been used to reduce image acquisition times primarily in contrast agent studies and via simulation in interventional MRI procedures. More recent simulations have suggested that improved definition of an interventional device [e.g., biopsy needles, radio frequency (RF) electrodes] could be achieved by rotating the keyhole pattern in k-space so that the read out direction lies perpendicular to the device orientation in real space. This study seeks to validate the earlier predictions of improved efficacy of a rotated stripes keyhole acquisition in actual in vitro and in vivo interventional MR imaging procedures. A true-FISP sequence was modified to perform central stripes keyhole (as known as conventional keyhole) acquisitions after a full initial reference data set was acquired. The gradients of this sequence were then modified to rotate the k-space definition and the keyhole stripes by 10°, 20°, 30°, 45°, and 60° from their conventional k-space orientation. Acquisitions were performed during insertion of interventional devices in phantom and in vivo RF ablation procedures, using the modified sequence selected which placed the phase encoding axis at parallel and perpendicular orientations to the devices. Resulting images were compared between the two orientations for needle width and tip accuracy. Apparent needle width was thinner and tip position more accurately determined for placement of phase encoding parallel to the needle in all cases. Rotated keyhole imaging provides the required temporal advantage of conventional keyhole imaging along with a near optimal definition of an interventional device when the phase encoding is oriented parallel to the direction of the needle motion. Magn Reson Med 42:554–560, 1999. © 1999 Wiley-Liss, Inc.

Improved device definition in interventional magnetic resonance imaging using a rotated stripes keyhole acquisition.

Keyhole acquisition techniques have been used to reduce image acquisition times primarily in contrast agent studies and via simulation in interventional MRI procedures. More recent simulations have suggested that improved definition of an interventional device [e.g., biopsy needles, radio frequency (RF) electrodes] could be achieved by rotating the keyhole pattern in k-space so that the read out direction lies perpendicular to the device orientation in real space. This study seeks to validate the earlier predictions of improved efficacy of a rotated stripes keyhole acquisition in actual in vitro and in vivo interventional MR imaging procedures. A true-FISP sequence was modified to perform central stripes keyhole (as known as conventional keyhole) acquisitions after a full initial reference data set was acquired. The gradients of this sequence were then modified to rotate the k-space definition and the keyhole stripes by 10 degrees, 20 degrees, 30 degrees, 45 degrees, and 60 degrees from their conventional k-space orientation. Acquisitions were performed during insertion of interventional devices in phantom and in vivo RF ablation procedures, using the modified sequence selected which placed the phase encoding axis at parallel and perpendicular orientations to the devices. Resulting images were compared between the two orientations for needle width and tip accuracy. Apparent needle width was thinner and tip position more accurately determined for placement of phase encoding parallel to the needle in all cases. Rotated keyhole imaging provides the required temporal advantage of conventional keyhole imaging along with a near optimal definition of an interventional device when the phase encoding is oriented parallel to the direction of the needle motion. Magn Reson Med 42:554-560, 1999.

Keyhole cone device for lateral magnification cerebral angiography

We have developed a new “keyhole” cone device for lateral magnification cerebral angiography. The keyhole lateral projection permits inclusion of the common carotid bifurcation, thereby eliminating the extra filming sequences and contrast injections required to delineate that structure. Magnification radiography has proved to be a valuable technique in the angiographic assessment of extracranial as well as intracranial vascular occlusive disease [1, 21. In addition, small focal spot magnification provides improved line pain resolution and permits lower patient radiation exposure dose. Because magnification radiography uses an air gap which produces a higher scatter radiation than conventional radiography, precise coning is imperative to avoid deterioration of the film image. Conventional coning devices cannot be used for magnification “keyhole” lateral projections because they are too long to permit the necessary 23 cm airgap between the head and the filmchanger and still maintain the required 100 cm target-to-film distance. Through a local vendor, we have developed a prototype lightweight (3 kg) magnification keyhole cone device that, at a target-to-film distance of 100 cm, permits an object-to-film air gap of 17.8-20.5 cm and has a magnification factor of 1.4. This device is interchangeable with larger, conventional keyhole cones. The only caution to potential users relates to the size of the cone base which varies with different models and manufacturers. The device described here has been tested by us in over 400 cerebral arteniognams and has produced films of excellent diagnostic quality. It has been used for anteroposterior magnification as well as lateral projections. The anteropostenior projection is accomplished by elevating the table to the level of the desired air gap. It has been our practice to employ the keyhole cone on all patients suspected of cerebrovascular occlusive disease and appropriate tumor suspects. The dimensions of the magnification keyhole cone are shown in figure 1 . In figure 2 the device is shown in use in a mock angiographic situation, and figure 3 demonstrates the quality of the resulting angiogram.