Faster Scan Times Research Articles

Preclinical assessment of a new magnetic resonance-based technique for determining bone quality by characterization of trabecular microarchitecture.

The utility of HR-CT to study longitudinal changes in bone microarchitecture is limited by subject radiation exposure. Although MR is not subject to this limitation, it is limited both by patient movement that occurs during prolonged scanning at distal sites, and by the signal-to-noise ratio that is achievable for high-resolution images in a reasonable scan time at proximal sites. Recently, a novel MR-based technique, fine structure analysis (FSA) (Chase et al. Localised one-dimensional magnetic resonance spatial frequency spectroscopy. PCT/US2012/068284 2012, James and Chase Magnetic field gradient structure characteristic assessment using one-dimensional (1D) spatial frequency distribution analysis. 7932720 B2, 2011) has been developed which provides both high-resolution and fast scan times, but which generates at a designated set of spatial positions (voxels) a one-dimensional signal of spatial frequencies. Appendix 1 provides a brief introduction to FSA. This article describes an initial exploration of FSA for the rapid, non-invasive characterization of trabecular microarchitecture in a preclinical setting. For L4 vertebrae of sham and ovariectomized (OVX) rats, we compared FSA-generated metrics with those from CT datasets and from CT-derived histomorphometry parameters, trabecular number (Tb.N), bone volume density (BV/TV), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp). OVX caused a reduction of the higher frequency structures that correspond to a denser trabecular lattice, while increasing the preponderance of lower frequency structures, which correspond to a more open lattice. As one example measure, the centroid of the FSA spectrum (which we refer to as fSAcB) showed strong correlation in the same region with CT-derived histomorphometry values: Tb.Sp: r -0.63, p < 0.001; Tb.N: r 0.71, p < 0.001; BV/TV: r 0.64, p < 0.001, Tb.Th: r 0.44, p < 0.05. Furthermore, we found a 17.5% reduction in fSAcB in OVX rats (p < 0.0001). In a longitudinal study, FSA showed that the age-related increase in higher frequency structures was abolished in OVX rats, being replaced with a 78-194% increase in lower frequency structures (2.4-2.8 objects/mm range), indicating a more sparse trabecular lattice (p < 0.05). The MR-based fine structure analysis enables high-resolution, radiation-free, rapid quantification of bone structures in one dimension (the specific point and direction being chosen by the clinician) of the spine.

Fast susceptibility-weighted imaging with three-dimensional short-axis propeller (SAP)-echo-planar imaging.

Susceptibility-weighted imaging (SWI) in neuroimaging can be challenging due to long scan times of three-dimensional (3D) gradient recalled echo (GRE), while faster techniques such as 3D interleaved echo-planar imaging (iEPI) are prone to motion artifacts. Here we outline and implement a 3D short-axis propeller echo-planar imaging (SAP-EPI) trajectory as a faster, motion-correctable approach for SWI. Experiments were conducted on a 3T MRI system. The 3D SAP-EPI, 3D iEPI, and 3D GRE SWI scans were acquired on two volunteers. Controlled motion experiments were conducted to test the motion-correction capability of 3D SAP-EPI. The 3D SAP-EPI SWI data were acquired on two pediatric patients as a potential alternative to 2D GRE used clinically. The 3D GRE images had a better target resolution (0.47 × 0.94 × 2 mm, scan time = 5 min), iEPI and SAP-EPI images (resolution = 0.94 × 0.94 × 2 mm) were acquired in a faster scan time (1:52 min) with twice the brain coverage. SAP-EPI showed motion-correction capability and some immunity to undersampling from rejected data. While 3D SAP-EPI suffers from some geometric distortion, its short scan time and motion-correction capability suggest that SAP-EPI may be a useful alternative to GRE and iEPI for use in SWI, particularly in uncooperative patients.

On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner

A new primary standard method for calibrating optical particle counters (OPC) has been developed based on quantitative gravitational deposition on a silicon wafer and accurate counting of the particles by a wafer surface scanner (WSS). The test aerosol consists of 3-μm diameter monodisperse polystyrene latex (PSL) spheres at concentrations in the range of 0.1 cm−3 to 1 cm−3. A key element to the calibration is the ability to generate monodisperse PSL spheres without residue particles by use of a virtual impactor and differential mobility analyzer. The use of these devices reduced the percentage of residue particles from more than 99.98% to about 5%. The expanded relative uncertainty (95% confidence level) in the number concentration determined with a WSS for a deposition of 200 particles is 17.8%. The major uncertainty component arises from the Poisson fluctuations in the aerosol concentration because of the low concentration. This methodology has advantages of a fast scanning time by the WSS of minutes c...

CCN Data Interpretation Under Dynamic Operation Conditions

We have developed a new numerical model for the non-steady-state operation of the Droplet Measurement Technologies (DMT) Cloud Condensation Nuclei (CCN) counter. The model simulates the Scanning Flow CCN Analysis (SFCA) instrument mode, where a wide supersaturation range is continuously scanned by cycling the flow rate over 20–120 s. Model accuracy is verified using a broad set of data which include ammonium sulfate calibration data (under conditions of low CCN concentration) and airborne measurements where either the instrument pressure was not controlled or where exceptionally high CCN loadings were observed. It is shown here for the first time that small pressure and flow fluctuations can have a disproportionately large effect on the instrument supersaturation due to localized compressive/expansive heating and cooling. The model shows that, for fast scan times, these effects can explain the observed shape of the SFCA supersaturation-flow calibration curve and transients in the outlet droplet sizes. The extent of supersaturation depletion from the presence of CCN during SFCA operation is also examined; we found that depletion effects can be neglected below 4000 cm−3 for CCN number. Copyright 2014 American Association for Aerosol Research

Non‐Cartesian parallel imaging reconstruction

Non-Cartesian parallel imaging has played an important role in reducing data acquisition time in MRI. The use of non-Cartesian trajectories can enable more efficient coverage of k-space, which can be leveraged to reduce scan times. These trajectories can be undersampled to achieve even faster scan times, but the resulting images may contain aliasing artifacts. Just as Cartesian parallel imaging can be used to reconstruct images from undersampled Cartesian data, non-Cartesian parallel imaging methods can mitigate aliasing artifacts by using additional spatial encoding information in the form of the nonhomogeneous sensitivities of multi-coil phased arrays. This review will begin with an overview of non-Cartesian k-space trajectories and their sampling properties, followed by an in-depth discussion of several selected non-Cartesian parallel imaging algorithms. Three representative non-Cartesian parallel imaging methods will be described, including Conjugate Gradient SENSE (CG SENSE), non-Cartesian generalized autocalibrating partially parallel acquisition (GRAPPA), and Iterative Self-Consistent Parallel Imaging Reconstruction (SPIRiT). After a discussion of these three techniques, several potential promising clinical applications of non-Cartesian parallel imaging will be covered.

Methods of discovery-based and targeted metabolite analysis by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detection.

The investigation of naturally volatile and derivatized metabolites in biological tissues by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS) can provide highly complex and information-rich data for comprehensive metabolomics analysis. The addition of the second separation dimension with GC × GC provides additional chemical selectivity, and the fast scanning time of TOFMS offers benefits in chemical selectivity and overall peak capacity compared to traditional one-dimensional (1D) GC. Furthermore, methods of derivatization to facilitate volatility and thermal stability, the most prominent being the silylation of organic compounds, have extended the use of GC as an important metabolomics tool. The highly information-rich data from GC × GC-TOFMS benefits from sophisticated comprehensive targeted and nontargeted algorithmic software methods. Herein, we detail a robust derivatization and instrumental method for metabolomics analysis and provide a brief overview of possible methods for data analysis.

A comparative numerical study of rotating and stationary RF coils in terms of flip angle and specific absorption rate for 7 T MRI

While high-field magnetic resonance imaging promises improved image quality and faster scan time, it is affected by non-uniform flip angle distributions and unsafe specific absorption rate levels within the patient, as a result of the complicated radiofrequency (RF) field – tissue interactions. This numerical study explored the possibility of using a single mechanically rotating RF coil for RF shimming and specific absorption rate management applications at 7T. In particular, this new approach (with three different RF coil element arrangements) was compared against both an 8-channel parallel coil array and a birdcage volume coil, with and without RF current optimisation. The evaluation was conducted using an in-house developed and validated finite-difference time-domain method in conjunction with a tissue-equivalent human head model. It was found that, without current optimisation, the rotating RF coil method produced a more uniform flip angle distribution and a lower maximum global and local specific absorption rate compared to the 8-channel parallel coil array and birdcage resonator. In addition, due to the large number of degrees of freedom in the form of rotated sensitivity profiles, the rotating RF coil approach exhibited good RF shimming and specific absorption rate management performance. This suggests that the proposed method can be useful in the development of techniques that address contemporary RF issues associated with high-field magnetic resonance imaging.

Diagnostic value of whole-body low-dose computed tomography (WBLDCT) in bone lesions detection in patients with multiple myeloma (MM)

PurposeTo assess the role of whole-body low-dose computed tomography (WBLDCT) in the diagnosis and staging of patients with suspicion of multiple myeloma (MM). Materials and methodsA total of 138 patients (76 male and 62 female; mean age 63.5 years, range 50–81 years), with early MM, underwent WBLDCT protocol study, performed on 16-slice scanner (Brilliance, Philips Medical System, Eindhoven, The Netherlands): tube voltage 120kV; tube current time product 40mAs. Diagnosis of osteolytic lesions was performed on the basis of axial and multiplanar reformatted images, whereas the assessment of spinal misalignment and fracture was done by using multiplanar reformatted images. The overall dose delivered to each patient was 4.2mSv. Every patient gave personal informed consent, as required by our institution guidelines. ResultsThe diagnosis was established either by histopathology or imaging follow-up (size increase of over a period time). In all 138 patients, image resolution was diagnostic, enabling correct classification of multiple myeloma patients. WBLDCT showed a total of 328 pathologic bone findings in 81/138 patients. CT scanning resulted in complete evaluation of the bone lesions in these areas of the skeleton: skull (42), humerus (15), femur (20), ribs (7), scapulae (13), pelvis (35), clavicle (13), sternum (10), cervical (39), dorsal (65), lombar (48) and sacral rachis (21). In 40/81 bone involvement detected by CT was the only CRAB criterion present. Furthermore, WBLDCT demonstrated pleuro-pulmonary lesions in 20 patients (11 infective, 9 as MM localizations) and 1 renal neoplasia. ConclusionWBLDCT, detecting bone marrow localizations and demonstrating extra-osseous findings, with a fast scanning time and high resolution images, is a reliable imaging-based tool for a proper management of MM patients.

Three-dimensional magnetization-prepared imaging using a concentric cylinders trajectory

To develop new magnetization-prepared imaging schemes based on a three-dimensional (3D) concentric cylinders trajectory. The 3D concentric cylinders trajectory, which is robust to off-resonance effects and timing delays while requiring fewer excitations than a comparable 3D Cartesian (3DFT) sequence, is used as the readout for magnetization-prepared sequences exploiting its inherently centric-ordered structure. Two applications: (i) T1 -weighted brain imaging with an inversion-recovery-prepared radiofrequency-spoiled gradient-echo (IR-SPGR) sequence, (ii) non-contrast-enhanced (NCE) peripheral angiography with a magnetization-prepared balanced steady-state free precession (bSSFP) sequence are presented to demonstrate the effectiveness of the proposed method. For peripheral angiography, the scan efficiency is further improved by interleaving different preparations at different rates and by carefully designing the sampling geometry for an efficient parallel imaging method. In vivo brain scans with an IR-SPGR sequence and lower extremity scans with a magnetization-prepared bSSFP sequence for NCE peripheral angiography both demonstrate that the proposed sequences with concentric cylinders effectively capture the transient magnetization-prepared contrast with faster scan times than a corresponding 3DFT sequence. The application of peripheral angiography also shows the feasibility of the proposed interleaving schemes and parallel imaging method. The 3D concentric cylinders trajectory is a robust and efficient readout that is well-suited for magnetization-prepared imaging.

SU‐C‐134‐06: Guidance for CT Departments Desiring to Optimize Protocols for: Multiple Scanner Architectures

Purpose: Clinical protocol development must consider a CT scanners architecture both in hardware and software. Differences in tube output, beam collimation, availability of iterative reconstruction, etc., may only allow some protocols to be properly performed on higher end scanners due to clinical constraints like breath hold duration and contrast dynamics. This study presents an overview of techniques for translating and optimizing a protocol from one scanner to another. Cases in which protocols are not compatible with a given scanner architecture are also discussed. Methods: At our institution, intensive protocol optimization is performed for each protocol using a single scanner architecture. Once a protocol is optimized in both technical and clinical parameters, the protocol can be translated to other scanner architectures (both older and newer). Essential restraints on the translation process include the maximum clinically allowable scan time and the maximum tube output of the scanner. Successful translation can be done if scan parameters can be modified within these essential constraints. If this is not possible then compromises have to be made that can affect clinical performance. Mathematical relationships related to tube output and clinical considerations will be discussed that guide the transformation and any needed compromises. Results: Several test cases are presented providing details of translating optimized protocols to an older and newer CT scanner architecture. Cases in which older scanners cannot provide the required performance are common for angiography exams that require high spatial resolution, thin reconstructed slice thickness, low noise, and fast scan times due to breath hold and contrast dynamic constraints. Conclusion: Understanding the limitations of older generation CT scanners and the benefits of newer CT architectures is critical for maintaining a uniquely optimized set of CT protocols across a wide range of CT architectures. Equipment grant from GE healthcare.

Advanced large airway CT imaging in children: evolution from axial to 4-D assessment

Continuing advances in multidetector computed tomography (MDCT) technology are revolutionizing the non-invasive evaluation of congenital and acquired large airway disorders in children. For example, the faster scanning time and increased anatomical coverage that are afforded by MDCT are especially beneficial to children. MDCT also provides high-quality multiplanar 2-dimensional (2-D), internal and external volume-rendering 3-dimensional (3-D), and dynamic 4-dimensional (4-D) imaging. These advances have enabled CT to become the primary non-invasive imaging modality of choice for the diagnosis, treatment planning, and follow-up evaluation of various large airway disorders in infants and children. It is thus essential for radiologists to be familiar with safe and effective techniques for performing MDCT and to be able to recognize the characteristic imaging appearances of large airway disorders affecting children.

Quantifying Myocardial Oxygenation with Cardiac Magnetic Resonance Imaging

Myocardial ischemia, resulting from imbalance in myocardial oxygen supply and demand, can be quantitatively assessed by positron emission tomography (PET) with absolute measures of myocardial blood flow and oxygen consumption rate (MVO 2 ). Cardiac Magnetic Resonance (CMR) has notable advantages over PET, with no radiation, high spatial resolution, faster scan times, and excellent soft tissue contrast. We have developed and validated new quantitative CMR oximetry techniques, including measurements of hyperemic myocardial oxygen extraction fraction and MVO 2 through Fick's Law. These may lead to a new understanding of roles of myocardial microcirculation in myocardial ischemia. Other cardiac oximetry methods for directly quantifying MVO 2 with 17 O-labelled water are also under investigation. Quantitative CMR oximetry is a promising, non-invasive, non-radiation approach for exploring the myocardial metabolism's role in cardiac patients.

Advances in Nuclear Cardiac Instrumentation with a View Towards Reduced Radiation Exposure

Recent advances in nuclear cardiology instrumentation have enabled myocardial perfusion imaging (MPI) with improved image quality and faster scan times. These developments also can be exploited to reduce the effective radiation dose to the patient. In this review, we discuss these technologies including new single photon emission computed tomography (SPECT) and positron emission tomography (PET) scanners, as well as novel reconstruction software with regard to their potential for the reduction of the patient radiation dose. New advances in nuclear cardiology instrumentation will allow routine rest/stress MPI imaging with low radiation doses (<5mSv) and fast imaging times, even by the software-only solutions. It is possible to further reduce the MPI radiation dose to less than 2 to 3mSv range with standard acquisition times. PET perfusion imaging also can be performed with very low doses especially by the three-dimensional scanners allowing hybrid PET/computed tomographic angiography (CTA) imaging with low overall dose. In addition, stress-only protocols can be utilized to further reduce the radiation dose and the overall test time.

Magnetic Resonance Imaging will Replace Computer Tomography

The introduction of tomographic imaging revolutionized the way we look at medical images. Compared to X-ray projective image, Computer Tomography (CT) offers the possibility of analyzing anatomical structures on a three-dimensional, slice-to-slice approach. On the other hand, limitations of CT consist of poor soft tissue contrast and ionizing radiation [1], while the advantages are distortion-free images and fast scan times [2]. Indeed, CT has been the modality of choice in many applications, going from diagnostic imaging to image-guided therapeutic solutions [3,4]. The advent of Magnetic Resonance Imaging (MRI) represented a further quantum leap in tomographic imaging in that soft tissue contrast was dramatically superior to CT with no radiation dose. On the other hand, MRI suffered from image distortion and long scan times, as well as limitation in scanning regions where metal implants are present. MRI offers a wide range of contrast generation, which makes it probably the modality with the highest potential in the imaging arena. This is reflected in the introduction of new MRI sequences in the range of 5-10 per year.

Second generation gold nanobeacons for robust K-edge imaging with multi-energy CT

Spectral CT is the newest advancement in CT imaging technology, which enhances traditional CT images with the capability to image and quantify certain elements based on their distinctive K-edge energies. K-edge imaging feature recognizes high accumulations of targeted elements and presents them as colorized voxels against the normal grayscale X-ray background offering promise to overcome the relatively low inherent contrast within soft tissue and distinguish the high attenuation of calcium from contrast enhanced targets. Towards this aim, second generation gold nanobeacons (GNB(2)), which incorporate at least five times more metal than the previous generation was developed. The particles were synthesized as lipid-encapsulated, vascularly constrained (>120 nm) nanoparticle incorporating tiny gold nanoparticles (2-4 nm) within a polysorbate core. The choice of core material dictated to achieve a higher metal loading. The particles were thoroughly characterized by physicochemical techniques. This study reports one of the earlier examples of spectral CT imaging with gold nanoparticles demonstrating the potential for targeted in vitro and in vivo imaging and eliminates calcium interference with CT. The use of statistical image reconstruction shows high SNR may allow dose reduction and/or faster scan times.

(P1-13) Initial Experience with Mobile Computed Tomography in the Neurosurgery Intensive Care Unit in a Level-1 Trauma Center in India

BackgroundNeurosurgical patients require frequent Computed Tomographies (CTs) of the head, usually at short notice. A mobile CT may prove to be invaluable for these patients.ObjectivesTo review the usefulness of mobile CT in intensive care unit (ICU).MethodsThis review was carried out over a 14 month period (18 July 2009 till 31 August 2010). Administrative and clinical data were reviewed and analyzed. For the first 6 months, only the number of CT's done was available. However, data were collected prospectively starting 01 Jan 2010 to include variables such as Glasgow Coma Scale (GSC) ventilator status and pressor support at the time of CT scan. The average time to do a CT was 150 minutes (range 60–240 minutes). The mean number of people required for shifting the patient was 4(range 3–6). For, mobile CT the average time to do a CT was 27.4 minutes (range 7.8–47 minutes) and mean for manpower was 3 (range 3–4).ObservationsThe mobile CT was installed and became functional in the neurosurgery ICU on 18 July 2009. A total of 1,752 head CTs were performed during the study period, with an average of 4.8 CTs daily. Detailed prospective data were available (since 01 January 2010) on 1,023 patients. Of these patients, 75.9% (n = 776) were on ventilator, 72.3% (n = 740) were on sedation, and 5.6% (n = 57) were on pressor support at the time of CT. The mean GCS at the time of CT was 8.1 (range 3–15).ConclusionsMobile CT was found to be easy to use, with fast scanning time and excellent image quality. It proves to be beneficial for nurses as it requires less time, energy and manpower. The mobile CT is strongly recommended for any high volume neurosurgery department in the country.

Abstract SY03-01: Molecular imaging with cellular resolution and molecular specificity using miniaturized microscopes

Abstract The earliest malignant lesions are microscopic in size and may be characterized by abnormal cell surface markers and disrupted microanatomy. The challenge for early detection of cancer is effectively using these features to localize and characterize those early lesions that are likely to progress. For cancers of the gastrointestinal (GI) tract there are some predisposing conditions that identify high-risk regions, and justify microscopic analyses for detection, diagnosis and guided biopsy of small, early lesions. In addition, microscopic analyses are used for detection of tumor margins in resection of skin and breast cancer and may have utility in resection of cancers. Micro-optical designs are enabling the development of miniaturized microscopes that can reach inside the body to interrogate disease states with cellular resolution. In combination with molecular probes such instruments can be used to interrogate suspect lesions for early signs of malignancy and to determine if margins are clear. To enable molecular imaging with cellular resolution, we have developed miniaturized confocal fluorescence microscopes that are based on a dual-axis architecture. The dual-axis design enables the use of low numerical aperture lenses and a folded light path that is amenable to a small form factor and post objective scanning in the scan head. The design features of this microscope included axial and transverse resolutions comparable to that used by pathologists (5 µM), and a 0.5 × 0.5 × 0.5 mm 3-D field of view in an instrument that has an external diameter compatible with use in an endoscope for GI cancers, and that can reach into small cavities for guided resections. The first dual-axis confocal (DAC) microscope that has been used in a clinical study in the colon with these capabilities has a 5-mm external diameter and an excitation wavelength of 780 nm. To enable early detection we have developed and tested a number of optical probes for use as molecular markers, and evaluated FDA-approved dyes as contrast for analysis of microanatomy. Studies in animals and man demonstrated the ability to observe microanatomy and discriminate malignant tissue from surrounding normal tissues. A wide variety of fluorescent agents are being developed and tested for cancer detection using macroscopic approaches. These agents can be detected at the cellular level with miniaturized microscopes for complementary analyses. Placement of the microscope can be guided by the macroscopic images, and the microscopic data can be used to substantiate the images. We have targeted surface markers and the cytoplasmic enzyme Cox-2 in these studies. We fitted the DAC microscopes with a needle lens to reach deep into the tissues and this instrument has been evaluated for guided resections of medulloblastoma in preclinical studies. The next-generation instruments have a smaller form factor and are designed for multispectral capabilities and faster scan times. This will increase their utility with increased access to tissues sites and multiplexed in vivo assays. The co-development of molecular probes and micro-optical instruments to visualize cancer may improve detection of cancer, and can be used to assess therapeutic outcome. Advances in in vivo microscopy could lead to a fundamental shift in the diagnostic paradigm from biopsy with conventional histopathology to performance of point-of-care morphologic diagnosis using in vivo microscopic pathology. These technologies are closing the gap between the patient and the diagnostic event, and will have major ramifications for the training of future physicians to interpret real-time in vivo microscopic molecular data, and will advance the emerging field of telepathology. One of the features of multimodality molecular imaging is reaching across a range of scales from microscopic, cellular resolution, to macroscopic, whole body, imaging and new tools with microscopic capabilities are necessary to achieve these aims Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY03-01. doi:10.1158/1538-7445.AM2011-SY03-01

Iterative reconstruction for coronary CT angiography: finding its way

Image reconstruction algorithms play a critical role in defining the quality and integrity of medical imaging using computed tomography. Since the advent of CT, image reconstruction has largely been performed by filtered back projection (FBP). This reconstruction technique has served CT well particularly at a time when there were significant limitations in computer processing capabilities. Iterative image reconstruction algorithms were, in fact available and were used to generate images with the very first commercial clinical computed tomographic (CT) scanner. This technique did not see significant adoption in clinical CT use owing to the ease of implementation and the faster image reconstruction of filtered back projection. Over the past decade, the need for finer resolution, greater volume coverage, faster scan times and the desire to lower radiation dose at the same time have pushed the performance of FBP reconstruction to its limits. Recently, there has been a re-introduction of iterative reconstruction for CT imaging with recently published studies in other organ systems showing that iterative reconstructions can produce higher-resolution images with greater robustness for the reduction of various imaging artifacts. There has been subsequent early adoption and experience with iterative reconstruction in coronary CT angiography (CCTA). We herein review the various iterative reconstruction platforms released for use for CCTA and the initial experiences implementing and integrating these reconstruction algorithms in clinical practice.

A comprehensive study on decreasing the kilovoltage cone‐beam CT dose by reducing the projection number

The objective of this study was to evaluate the effect of kilovoltage cone‐beam computed tomography (CBCT) on registration accuracy and image qualities with a reduced number of planar projections used in volumetric imaging reconstruction. The ultimate goal is to evaluate the possibility of reducing the patient dose while maintaining registration accuracy under different projection‐number schemes for various clinical sites. An Elekta Synergy Linear accelerator with an onboard CBCT system was used in this study. The quality of the Elekta XVI cone‐beam three‐dimensional volumetric images reconstructed with a decreasing number of projections was quantitatively evaluated by a Catphan phantom. Subsequently, we tested the registration accuracy of imaging data sets on three rigid anthropomorphic phantoms and three real patient sites under the reduced projection‐number (as low as 1/6th) reconstruction of CBCT data with different rectilinear shifts and rotations. CBCT scan results of the Catphan phantom indicated the CBCT images got noisier when the number of projections was reduced, but their spatial resolution and uniformity were hardly affected. The maximum registration errors under the small amount transformation of the reference CT images were found to be within 0.7 mm translation and 0.3° rotation. However, when the projection number was lower than one‐fourth of the full set with a large amount of transformation of reference CT images, the registration could easily be trapped into local minima solutions for a nonrigid anatomy. We concluded, by using projection‐number reduction strategy under conscientious care, imaging‐guided localization procedure could achieve a lower patient dose without losing the registration accuracy for various clinical sites and situations. A faster scanning time is the main advantage compared to the mA decrease‐based, dose‐reduction method.PACS numbers: 87.57.C‐, 87.57.cf, 87.57.cj, 87.57.cm, 87.57.cp, 87.57.N‐, 87.57.nf, 87.57.nj

Clinical application of 320-row multidetector computed tomography for a dynamic three-dimensional vascular study: Imaging findings and initial experience

The 320-row multidetector computed tomography (MDCT) is now used by both cardiologists and neurosurgeons. It enables dynamic 3D-CT angiography, because the wide-area detector eliminates helical scanning, thus achieving very fast scanning times for single 3D-CT volume data. Some microvascular surgeons are familiar with 64-row MDCT for perforator studies, but there are few reports of studies using 320-row MDCT. This MDCT system was used to follow the dynamic blood flow of small vessels. It is considered to have a great potential in the clinical field of microvascular surgery.