Quantitative Computed Tomography (QCT) of the Distal Forearm in Men Using a Spiral Whole-Body CT Scanner - Description of a Method and Reliability Assessment of the QCT Pro Software

The Mr F study investigates the pathogenesis of low trauma distal forearm fractures in men and includes volumetric bone mineral density (vBMD) measurements at the ultradistal forearm as there are no current data. A standard 64 slice CT scanner was used to determine if it was possible to adapt the existing Mindways quantitative computed tomography Pro software for measuring vBMD values at the hip and spine sites. For calculation of intra- and interobserver reliability 40 forearm scans out of the 300 available were chosen randomly. The images were analyzed using the Slice Pick module and Bone Investigational Toolkit. The 4% length of the radius was chosen by measuring the length of the radius from the scaphoid fossa distally to the radial head. The acquired image then underwent extraction, isolation, rotation, and selection of region of interest in order to generate a report on vBMD. A cross-sectional image was created to allow the generation of data on the cortical and trabecular components separately. Repeat analyses were undertaken by 3 independent observers who were blinded as to whether the image was from a participant with or without fracture. The images were presented in random order at each time point. The following parameters were recorded: cortical cross sectional area, total vBMD, trabecular vBMD, and cortical vBMD (CvBMD). Data were analyzed by calculating intraclass correlation coefficients for intra- and interobserver reliability. The lowest values occurred at the CvBMD with intraobserver reliability of 0.92 (95% confidence interval [CI] of 0.86-0.96) and interobserver reliability of 0.92 (95% CI 0.89-0.96). All other parameters had reliability values between 0.97 and 0.99 with tighter 95% CI than for CvBMD. The method of adapting the Mindways Pro software using a standard CT to produce vBMD and structural data at the ultradistal radius is reliable.

Volumetric CT with sparse detector arrays (and application to Si-strip photon counters)

Novel x-ray medical imaging sensors, such as photon counting detectors (PCDs) and large area CCD and CMOS cameras can involve irregular and/or sparse sampling of the detector plane. Application of such detectors to CT involves undersampling that is markedly different from the commonly considered case of sparse angular sampling. This work investigates volumetric sampling in CT systems incorporating sparsely sampled detectors with axial and helical scan orbits and evaluates performance of model-based image reconstruction (MBIR) with spatially varying regularization in mitigating artifacts due to sparse detector sampling. Volumetric metrics of sampling density and uniformity were introduced. Penalized-likelihood MBIR with a spatially varying penalty that homogenized resolution by accounting for variations in local sampling density (i.e. detector gaps) was evaluated. The proposed methodology was tested in simulations and on an imaging bench based on a Si-strip PCD (total area 5 cm  ×  25 cm) consisting of an arrangement of line sensors separated by gaps of up to 2.5 mm. The bench was equipped with translation/rotation stages allowing a variety of scanning trajectories, ranging from a simple axial acquisition to helical scans with variable pitch. Statistical (spherical clutter) and anthropomorphic (hand) phantoms were considered. Image quality was compared to that obtained with a conventional uniform penalty in terms of structural similarity index (SSIM), image uniformity, spatial resolution, contrast, and noise. Scan trajectories with intermediate helical width (~10 mm longitudinal distance per 360° rotation) demonstrated optimal tradeoff between the average sampling density and the homogeneity of sampling throughout the volume. For a scan trajectory with 10.8 mm helical width, the spatially varying penalty resulted in significant visual reduction of sampling artifacts, confirmed by a 10% reduction in minimum SSIM (from 0.88 to 0.8) and a 40% reduction in the dispersion of SSIM in the volume compared to the constant penalty (both penalties applied at optimal regularization strength). Images of the spherical clutter and wrist phantoms confirmed the advantages of the spatially varying penalty, showing a 25% improvement in image uniformity and 1.8  ×  higher CNR (at matched spatial resolution) compared to the constant penalty. The studies elucidate the relationship between sampling in the detector plane, acquisition orbit, sampling of the reconstructed volume, and the resulting image quality. They also demonstrate the benefit of spatially varying regularization in MBIR for scenarios with irregular sampling patterns. Such findings are important and integral to the incorporation of a sparsely sampled Si-strip PCD in CT imaging.

Image Quality of 3rd Generation Spiral Cranial Dual-Source CT in Combination with an Advanced Model Iterative Reconstruction Technique: A Prospective Intra-Individual Comparison Study to Standard Sequential Cranial CT Using Identical Radiation Dose

Objectives

To prospectively intra-individually compare image quality of a 3^rd generation Dual-Source-CT (DSCT) spiral cranial CT (cCT) to a sequential 4-slice Multi-Slice-CT (MSCT) while maintaining identical intra-individual radiation dose levels.

Methods

35 patients, who had a non-contrast enhanced sequential cCT examination on a 4-slice MDCT within the past 12 months, underwent a spiral cCT scan on a 3^rd generation DSCT. CTDI_vol identical to initial 4-slice MDCT was applied. Data was reconstructed using filtered backward projection (FBP) and 3^rd-generation iterative reconstruction (IR) algorithm at 5 different IR strength levels. Two neuroradiologists independently evaluated subjective image quality using a 4-point Likert-scale and objective image quality was assessed in white matter and nucleus caudatus with signal-to-noise ratios (SNR) being subsequently calculated.

Results

Subjective image quality of all spiral cCT datasets was rated significantly higher compared to the 4-slice MDCT sequential acquisitions (p<0.05). Mean SNR was significantly higher in all spiral compared to sequential cCT datasets with mean SNR improvement of 61.65% (p*_{Bonferroni0.05}<0.0024). Subjective image quality improved with increasing IR levels.

Conclusion

Combination of 3^rd-generation DSCT spiral cCT with an advanced model IR technique significantly improves subjective and objective image quality compared to a standard sequential cCT acquisition acquired at identical dose levels.

[Performance evaluation of CT automatic exposure control on fast dual spiral scan]

The performance of individual computed tomography automatic exposure control (CT-AEC) is very important for radiation dose reduction and image quality equalization in CT examinations. The purpose of this study was to evaluate the performance of CT-AEC in conventional pitch mode (Normal spiral) and fast dual spiral scan (Flash spiral) in a 128-slice dual-source CT scanner. To evaluate the response properties of CT-AEC in the 128-slice DSCT scanner, a chest phantom was placed on the patient table and was fixed at the center of the field of view (FOV). The phantom scan was performed using Normal spiral and Flash spiral scanning. We measured the effective tube current time product (Eff. mAs) of simulated organs in the chest phantom along the longitudinal (z) direction, and the dose dependence (distribution) of in-plane locations for the respective scan modes was also evaluated by using a 100-mm-long pencil-type ionization chamber. The dose length product (DLP) was evaluated using the value displayed on the console after scanning. It was revealed that the response properties of CT-AEC in Normal spiral scanning depend on the respective pitches and Flash spiral scanning is independent of the respective pitches. In-plane radiation dose of Flash spiral was lower than that of Normal spiral. The DLP values showed a difference of approximately 1.7 times at the maximum. The results of our experiments provide information for adjustments for appropriate scanning parameters using CT-AEC in a 128-slice DSCT scanner.

Strahlendosis und Möglichkeiten zur Dosisreduktion in der Mehrschicht-CT

Since its introduction a few years ago, multidetector row CT (MDCT) has become a widely used diagnostic procedure and has been proven to be a valuable tool for various indications. A major issue using this new modality is the inherent risk of applying increased radiation exposure, when compared to single-slice CT or other imaging modalities.However, MDCT offers some valuable options to save radiation exposure, such as choosing optimized exposure parameters or its superior dose efficiency in comparison to single-slice CT. Multi-phasic examinations should be restricted to indications where definitely necessary. Modern scanners offer intelligent tools for further reduction of radiation dose, such as ECG- or bodyshape-based realtime dose modulation. A new field of applications is the low-dose CT for early detection of diseases. While acquiring thin slices with high spatial resolution, the dose can be reduced to similar values as in conventional radiography, especially when examining under high-contrast conditions. Using all these various options available, radiation exposure can sometimes even be lower than using a conventional single-slice helical CT.

Frühes klinisches Management nach Polytrauma mit 1- und 4-Schicht-Spiral-CT

In the early clinical phase the comprehensive imaging of patients with multiple trauma using helical CT is already established. Aim of this study was to assess whether MSCT may improve the patient management and the diagnostic results. The procedure is designed as follows: after life-thretening treatment x-ray of chest and ultrasound are carried out in the emergency room. Then the patient is moved to CT. From 1998 to december 2000 241 patients were examined using a single slice helical CT (Somatom plus 4), in 2001 79 patients using a 4-slice helical CT (Somatom VZ, Siemens Med.Sol.). After CT selected radiograms of the extremities were taken. 359 of 360 procedures were carried out successfully. Excluding 1 case (death during 1-sl.h CT) all relevant lesions of head, neck, and body were diagnosed. Although the patients had an injury severity score of approximately 30. The change from 1 slice-helical CT to 4 slice-helical CT allowed us to reduce the stay in the CT room from 28 to 16 min. The total lethality decreased by approximately 4%. Advantages for the patient arose from the standardized examination protocol using multislice CT. If integrated in an interdisciplinary management concept, it is a good compromise between examination time, comprehensive diagnostic imaging, life-saving therapeutic procedures, and therapy planning.

[Use of megavoltage CT(MVCT) in helical tomotherapy for head and neck dose calculation]

OBJECTIVE

To evaluate the feasibility and accuracy of using Megavoltage CT(MVCT) for head and neck dose calculation.

METHODS

The cheese Phantom was imaged using MVCT scanner, and the MVCT value density calibration curve was established. Conventional CT and MVCT image of nasopharyngeal carcinoma was acquired respectively, and IMRT plan was designed on conventional CT image of NPC patient. The conventional CT plan was copied to MVCT image. The dose distribution was calculated for tumor and normal tissue using the MVCT value density calibration curve, and compared with that of conventional CT. Ten NPC patients were collected for dose verification of IMRT plan on MVCT images.

RESULTS

The MVCT numbers depended linearly on the electron density of the sample, and the stability of the MVCT numbers to electron density was good.The error between the measured dose and calculated dose in measured point was less than 3%.The isodose distribution was well agreement with that calculated by planning system.

CONCLUSIONS

Performing dose recalculation using MVCT of Tomotherapy in head and neck region was feasible.and the dose distributions on kVCT and MVCT were in excellent agreement.

Multidetector-row computed tomography for noninvasive coronary imaging

Computed tomography (CT) permits cross-sectional imaging of the heart. Temporal and spatial resolutions of the technique have been insufficient to cover the heart without motion artefacts until the recent advent of multidetector systems with more than 16 detector rows. The modality is now suited for noninvasive imaging of the coronary arteries, producing detailed morphologic images of the entire coronary tree with upto 0.4 mm of spatial resolution, within a single short breath-hold duration. CT imaging goes beyond the delineation of the coronary lumen as provided by selective invasive angiography; the plaque burden of the coronary artery wall can be visualized directly, utilizing soft-tissue contrast and a high sensitivity even for the small calcifications that are present in hard plaque formations. Therefore, CT combines elements of catheterization angiography for lumen imaging and of intravascular ultrasound imaging for coronary wall imaging. However current CT technology is not yet able to compete with the temporal or spatial resolution of catheterization angiography nor does it provide the detailed spatial or contrast resolution of intravascular ultrasound imaging. At present, its use is therefore restricted to complementing the invasive modalities in appropriate indications. Although CT entails significantly less risk than the invasive procedures, the risks of radiation dose exposure and contrast agent application are not negligible. In the foreseeable future, if the current rate of technological advancement continues, CT may replace the invasive modalities in routine care for diagnostic purposes.

A stationary computed tomography system with cylindrically distributed sources and detectors

BACKGROUND

The temporal resolution of current computed tomography (CT) systems is limited by the rotation speed of their gantries.

OBJECTIVE

A helical interlaced source detector array (HISDA) CT, which is a stationary CT system with distributed X-ray sources and detectors, is presented in this paper to overcome the aforementioned limitation and achieve high temporal resolution.

METHODS

Projection data can be obtained from different angles in a short time and do not require source, detector, or object motion. Axial coverage speed is increased further by employing a parallel scan scheme. Interpolation is employed to approximate the missing data in the gaps, and then a Katsevich-type reconstruction algorithm is applied to enable an approximate reconstruction.

RESULTS

The proposed algorithm suppressed the cone beam and gap-induced artifacts in HISDA CT. The results also suggest that gap-induced artifacts can be reduced by employing a large helical pitch for a fixed gap height.

CONCLUSIONS

HISDA CT is a promising 3D dynamic imaging architecture given its good temporal resolution and stationary advantage.

Comparison of radiation dose estimates, image noise, and scan duration in pediatric body imaging for volumetric and helical modes on 320-detector CT and helical mode on 64-detector CT

BACKGROUND

Advanced multidetector CT systems facilitate volumetric image acquisition, which offers theoretic dose savings over helical acquisition with shorter scan times.

OBJECTIVE

Compare effective dose (ED), scan duration and image noise using 320- and 64-detector CT scanners in various acquisition modes for clinical chest, abdomen and pelvis protocols.

MATERIALS AND METHODS

ED and scan durations were determined for 64-detector helical, 160-detector helical and volume modes under chest, abdomen and pelvis protocols on 320-detector CT with adaptive collimation and 64-detector helical mode on 64-detector CT without adaptive collimation in a phantom representing a 5-year-old child. Noise was measured as standard deviation of Hounsfield units.

RESULTS

Compared to 64-detector helical CT, all acquisition modes on 320-detector CT resulted in lower ED and scan durations. Dose savings were greater for chest (27-46%) than abdomen/pelvis (18-28%) and chest/abdomen/pelvis imaging (8-14%). Noise was similar across scanning modes, although some protocols on 320-detector CT produced slightly higher noise.

CONCLUSION

Dose savings can be achieved for chest, abdomen/pelvis and chest/abdomen/pelvis examinations on 320-detector CT compared to helical acquisition on 64-detector CT, with shorter scan durations. Although noise differences between some modes reached statistical significance, this is of doubtful diagnostic significance and will be studied further in a clinical setting.

[Design and accuracy analysis of upper slicing system of MSCT]

The upper slicing system is the main components of the optical system in MSCT. This paper focuses on the design of upper slicing system and its accuracy analysis to improve the accuracy of imaging. The error of slice thickness and ray center by bearings, screw and control system were analyzed and tested. In fact, the accumulated error measured is less than 1 microm, absolute error measured is less than 10 microm. Improving the accuracy of the upper slicing system contributes to the appropriate treatment methods and success rate of treatment.

[Verification of the couch automatic movement accuracy for Hi-ART tomotherapy]

The QUASAR Penta-guide Phantom with fiducial markers was scanned, and the CT images were transferred to Pinnacle workstation. Skin and target volumes were contoured and transferred to TomoPlan treatment planning system. The phantom was scanned with Megavoltage CT (MVCT). MVCT images were matched to the planning CT. Automatic adjustment of treatment couch was completed. It was found that the green laser coincided with the etched center crosshairs in lateral and longitudinal directions with an error less than 2 mm. However 2 mm vertical tabletop lag was found, but could be eventually corrected. Verifications for specific patients with head and pelvic tumors were also completed, the residual setup error were analyzed. The automatic movement of tabletop after image match is satisfactory.

[Manual handling of defective channels in siemens somatom Sensation 16 CT]

The present paper introduces the components and operating principle of Sensation 16 CT date measuring system (DMS), analyzes the fixed position of modules and channels in array detector modules (ADM), the Checkup table, Tuneup table and IRS table in ICS Syngo Service. The author also puts forward a solution of manual handling of defective channels.

Feasibility of tomotherapy for Graves' ophthalmopathy: Dosimetry comparison with conventional radiotherapy

PURPOSE

To compare the dosimetry of tomotherapy and the conventional half-beam technique (HBT) or non-split beam technique (NSBT) for target coverage and radiation dose to the lacrimal glands and lens.

PATIENTS AND METHODS

A retrospective review of 7 patients with Graves' ophthalmopathy who had radiotherapy because of disease progression on high steroid dose is reported: 3 patients were treated with tomotherapy and 4 patients with HBT.

RESULTS

Compared to HBT, tomotherapy may provide better target coverage and significant reduction of radiation dose to the lacrimal glands and a higher dose to the lens. The NSBT improved target coverage but resulted in significantly higher doses to the lens and lacrimal glands.

CONCLUSION

Tomotherapy may provide better coverage of the target volume and may be more effective in reducing severe exophthalmos compared to the conventional radiotherapy technique.

[Impact of planning CT slice thickness on the accuracy of automatic target registration using the on-board cone-beam CT]

We have evaluated relationship between planning CT slice thickness and the accuracy of automatic target registration using cone-beam CT (CBCT). Planning CT images were acquired with reconstructed slice thickness of 1, 2, 3, 5, and 10mm for three different phantoms: Penta-Guide phantom, acrylic ball phantom, and pelvic phantom. After correctly placing the phantom at the isocenter using an in-room laser, we purposely displaced it by moving the treatment couch and then obtained CBCT images. Registration between the planning CT and the CBCT was performed using automatic target registration software, and the registration errors were recorded for each planning CT data set with different slice thickness. The respective average and standard deviation of errors for 10 mm slice thickness CT in the lateral, longitudinal, and vertical directions (n=15 data sets) were: 0.7 +/- 0.2mm, 0.8 +/- 0.2mm, and 0.2 +/- 0.2mm for the Penta-Guide phantom; 0.5 +/- 0.4 mm, 0.6 +/- 0.3 mm, and 0.4 +/- 0.3 mm for the acrylic ball phantom; and 0.6 +/- 0.2 mm, 0.9 +/- 0.2 mm, and 0.2 +/- 0.2 mm for the pelvic phantom. We found that the mean registration errors were always less than 1 mm regardless of the slice thickness tested. The results suggest that there is no obvious correlation between the planning CT slice thickness and the registration errors.

[Comparison of radiation dose reduction of prospective ECG-gated one beat scan using 320 area detector CT coronary angiography and prospective ECG-gated helical scan with high helical pitch (FlashScan) using 64 multidetector-row CT coronary angiography]

BACKGROUND

A high radiation dose associated with 64 multidetector-row computed tomography (64-MDCT) is a major concern for physicians and patients alike. A new 320 row area detector computed tomography (ADCT) can obtain a view of the entire heart with one rotation (0.35 s) without requiring the helical method. As such, ADCT is expected to reduce the radiation dose. We studied image quality and radiation dose of ADCT compared to that of 64-MDCT in patients with a low heart rate (HR≤60).

METHODS

Three hundred eighty-five consecutive patients underwent 64-MDCT and 379 patients, ADCT. Patients with an arrhythmia were excluded. Prospective ECG-gated helical scan with high HP (FlashScan) in 64 was used for MDCT and prospective ECG-gated conventional one beat scan, for 320-ADCT. Image quality was visually evaluated by an image quality score. Radiation dose was estimated by DLP (mGy･cm) for 64-MDCT and DLP.e (mGy･cm) for 320-ADCT.

RESULTS

Radiation dose of 320-ADCT (208±48 mGy･cm) was significantly (P<0.0001) lower than that of 64-MDCT (484±112 mGy･cm), and image quality score of 320-ADCT (3.0±0.2) was significantly (P=0.0011) higher than that of 64-MDCT (2.9±0.4). Scan time of 320-ADCT (1.4±0.1 s) was also significantly (P<0.0001) shorter than that of 64-MDCT (6.8±0.6 s).

CONCLUSIONS

320-ADCT can achieve not only a reduction in radiation dose but also a superior image quality and shortening of scan time compared to 64-MDCT.

[Analysis of megavoltage computed tomography imaging on a helical tomotherapy unit]

OBJECTIVE

To evaluate the image quality of megavoltage computed Tomography imaging.

METHODS

The HU uniformity and linearity, image noise, spatial resolution, low contrast resolution and spatial linearity in MVCT mode were evaluated with Catphan 600 phantom, and the factor of pitch was also evaluated. Influencing factors of image quality were also discussed.

RESULTS

The MVCT values depended linearly on the physical density of the sample. The MVCT values uniformity was good. The spatial resolution was 4 lp/cm. The use of an MV Beam for imaging results in the loss of low contrast resolution, but it is sufficient for pretreatment image guidance. The geometric accuracy was good.

CONCLUSIONS

The image quality of MVCT is less than that of KVCT, but is good enough for IGRT.

Impact of new technologies on dose reduction in CT

The introduction of slip ring technology enables helical CT scanning in the late 1980's and has rejuvenated CT's role in diagnostic imaging. Helical CT scanning has made possible whole body scanning in a single breath hold and computed tomography angiography (CTA) which has replaced invasive catheter based angiography in many cases because of its easy of operation and lesser risk to patients. However, a series of recent articles and accidents have heightened the concern of radiation risk from CT scanning. Undoubtedly, the radiation dose from CT studies, in particular, CCTA studies, are among the highest dose studies in diagnostic imaging. Nevertheless, CT has remained the workhorse of diagnostic imaging in emergent and non-emergent situations because of their ubiquitous presence in medical facilities from large academic to small regional hospitals and their round the clock accessibility due to their ease of use for both staff and patients as compared to MR scanners. The legitimate concern of radiation dose has sparked discussions on the risk vs benefit of CT scanning. It is recognized that newer CT applications, like CCTA and perfusion, will be severely curtailed unless radiation dose is reduced. This paper discusses the various hardware and software techniques developed to reduce radiation dose to patients in CT scanning. The current average effective dose of a CT study is ∼10 mSv, with the implementation of dose reduction techniques discussed herein; it is realistic to expect that the average effective dose may be decreased by 2-3 fold.

[Assessment of parotid gland dose variations by helical tomotherapy adaptive system in head and neck cancer]

The paper introduces a helical tomotherapy (HT) adaptive system in assessment of parotid gland dose variation in head and neck cancer. The system, which helical therapy unit is equipped with, is based on megavoltage computed tomography (MVCT) images to calculate the actual volume and dose of region of interest (ROI). Whether to change plan is judged on the fact for the realization of adaptive radiotherapy. One case of nasopharyngeal carcinoma was as a sample to evaluate parotid gland dose variation during the treatment. On every week and last time, patient was scanned by MVCT before treatment, a total of eight MVCT images. As the treatment progressed, the parotid gland volume was shrinking and the dose was increasing. The parotids volume variation was negatively related with D50 and V1 (both P < 0.05).

What are the basic concepts of temporal, contrast, and spatial resolution in cardiac CT?

An imaging instrument can be characterized by its spatial resolution, contrast resolution, and temporal resolution. The capabilities of computed tomography (CT) relative to other cardiac imaging modalities can be understood in these terms. The purpose of this review is to characterize the spatial, contrast, and temporal resolutions of cardiac CT in practical terms.

[Multidetector computed tomography of the liver]

Multidetector-row CT (MDCT) scanners have dramatically improved liver imaging. With the newest generation of 40-64 row scanners, true isotropic imaging with a z-axis resolution of 0.3-0.6 mm has become possible. Acquisition time for the scan has been shortened to a few seconds. To fully exploit the advantages of MDCT scanners in liver imaging, the examination protocols have to be optimized with regard to contrast material flow rate, scan delay, and the number of scans performed. The possible advantages of double arterial phase scans in the detection of HCC are discussed. The clinical value of 3D reconstructions, such as multiplanar reconstructions and curved planar reconstructions, for assessment of the vascular and biliary duct infiltration is demonstrated. Optimized MDCT imaging improves detection and characterization of focal liver lesions.

[Dual-source variable pitch spiral CT reconstruction algorithm]

Computed tomography angiography (CTA) is a useful approach for diagnosing vascular diseases. In this paper, we proposed a reconstruction algorithm for dual-source spiral CT with variable pitch. The projection data are collected by the double-source double-multislice spiral CT (DSDMS-CT). However, the pitch of the DSDMS-CT is variable other than being constant. We have developed a new formula performing interpolation along Z-axis for dual-source spiral CT with variable pitch. The dual-source spiral CT with variable pitch can chase contrast bolus more flexibly and more effectively. The simulation results show the correctness and efficiency of the proposed algorithm.

Technological approaches to in-room CBCT imaging

The use of Cone-Beam Computed Tomography (CBCT) in Image-Guided Radiation Therapy (IGRT) has become increasingly feasible and popular in recent years. Advances and developments in Flat-Panel Imager (FPI) technology and image reconstruction software allow for linac-mounted 3D CBCT imaging. Taking CBCT images on a daily/weekly basis, offers the possibility to guide the treatment beam according to tumour motion and to apply changes to the treatment plan if necessary. This however raises the issue of additional imaging dose and thus increases in secondary cancer risk. The performance characteristics of kV-CBCT and MV-CBCT solutions currently offered by Elekta, Siemens and Varian are compared in this paper in terms of additional imaging dose and image quality. The review also outlines applications of CBCT for IGRT and Adaptive Radiotherapy (ART). As CBCT is not the only in-room IGRT platform, helical MV-CT (Tomotherapy) and in-room CT designs are also presented.

[Slice profile characteristics of MPR images in multi-slice CT]

Few studies have investigated the detailed imaging characteristics of multiplanar reconstruction (MPR) images, which have come to be used in imaging diagnosis. The purpose of this study was to evaluate the slice profile characteristics of MPR images. The slice profile of a coronal image was measured by the bead method. Moreover, it assumed that the slice profile of an MPR image became a convolution of the square profile corresponding to the nominal slice thickness and line spread function (LSF) of an axial image, and the simulation was performed. The nominal slice thicknesses of the original axial image and coronal image were 1.0 mm, 2.0 mm, and 3.0 mm. Three reconstruction kernels (B20, B30, and B40) of the original axial image were used. The results of measurement revealed that the full width at half maximum (FWHM) values were 1.7 mm for reconstruction kernel B20 and 1.3 mm for reconstruction kernel B40 in the case of a nominal slice thickness of 1.0 mm. The simulated and measured modulation transfer factors (MTF) were in close agreement. Then the slice profile of the coronal (sagittal) MPR image forms by the convolution of a LSF of the y- (x-) direction and the square profile with a nominal MPR slice width, and is affected by the reconstruction kernel.

[Effects of 16-multi-detector row CT aortography with lower tube current]

OBJECTIVE

To study the effects of 16-multi-detector row CT (MDCT) aortography with lower tube current in diagnosis of aortic diseases.

METHODS

The study was conducted in 2 steps. In the first step, 58 patients with suspicious aortic disease or after operation on the aorta underwent 16-MDCT aortography for 70 times. Ten of them underwent scanning with conventional tube current of 175 mAs and the other 60 patients were divided into 3 groups according to their bogy weights: <65 kg group (n=20) receiving the lowest tube current of 25 mAs, 65-75 kg group (n=20) receiving the lowest tube current of 50 mAs, and >75 kg group (n=20) receiving the lowest tube current of 75 mAs. In the second step 60 patients with dissecting aneurysm, underwent 16-MDST aortography and were divided into 3 groups according to their body weight too: <65 kg group (n=20) receiving the lowest tube current of 50 mAs, 65-75 kg group (n=20) receiving the lowest tube current of 75 mAs, and >75 kg group (n=20) receiving the lowest tube current of 100 mAs, all 25 mAs more compared with the corresponding groups in the first step. The weighted CT dose index (CTDI), scanning length, and dose length produce (DLP) were recorded. The diagnostic accuracy rates of the images from the low dose groups were compared with those of the higher dose groups.

RESULTS

The data of the first step showed that the CTDI values of the patients who received 25 mAs, 50 mAs, and 75 mAs tube current were 11.3%, 29.0%, and 42.7% that of the conventional tube current group (all P < 0.001) and the DLP values of the 3 low dose groups were also significantly lower than that of the conventional tube current group (all P < 0.001). The diagnostic accuracy rate of the 25 mAs, 50 mAs, and 75 mAs groups were 60% , 85%, and 85% that of the conventional tube current group. The results of the second step showed that the CTDI values of the 50 mAs, 75 mAs, and 100 mAs groups were 29.0%, 42.7%, and 57.3% that of the conventional tube current group respectively, and the DLP values of the 3 low dose groups were also significantly lower than that of the conventional group ( all P < 0. 001); and the 50 mAs, 75 mAs, and 100 mAs groups all showed good three-dimensional reconstruction imaging qualities, all with the diagnostic accuracy rate of 100%. The crossing section and three-dimensional images all showed excellent diagnostic image quality.

CONCLUSION

16-MDCT aortography with the tube current at the doses 50 mAs to 100 mAs suffices to diagnose aortic diseases in patients with different body weights. Higher tube current should be used in dissecting aneurysm. The tube current at the dose of 100 mAs satisfies the imaging and diagnosing of all kinds of aortic diseases in the patients with any body weight.

3 T contrast-enhanced magnetic resonance angiography for evaluation of the intracranial arteries: comparison with time-of-flight magnetic resonance angiography and multislice computed tomography angiography

PURPOSE

We sought to prospectively evaluate the image quality and visualization of the intracranial arteries using high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) at 3 T and to perform intraindividual comparison with time-of-flight (TOF) MRA and multislice CT angiography (CTA).

MATERIALS AND METHODS

Twelve patients (5 men, 7 women, 37-71 years of age) with suspected cerebrovascular disease prospectively underwent MRA and CTA. MRA was performed on a 3 T MR system, including both 3-dimensional (3D) TOF (Voxel dimension: 0.6 x 0.5 x 0.9 mm in 5 minutes and 40 seconds) and 3D CE-MRA (voxel dimension: 0.7 x 0.7 x 0.8 mm in 20 seconds, using parallel acquisition with an acceleration factor of 4). CTA images were acquired on a 16-slice CT scanner (voxel dimension: 0.35 x 0.35 x 0.8 mm in 17 seconds). The image quality and visualization of up to 26 intracranial arterial segments in each study was evaluated by 2 experienced radiologists. The arterial diameter for selective intracranial arteries was measured independently on each of the 3 studies, and statistical analysis and comparative correlation was performed.

RESULTS

A total of 312 arterial segments were examined by CE-MRA, TOF-MRA, and CTA. The majority of intracranial arteries (87%) were visualized with diagnostic image quality on CE-MRA with a significant correlation to TOF (R values = 0.84; 95% confidence interval 0.79-0.86, P < 0.0001), and to CTA (R values = 0.74; 95% confidence interavl 0.68-0.78, P < 0.001). The image quality for small intracranial arteries, including the anterior-inferior cerebellar artery, the posterior communicating artery, and the M3 branch of the middle cerebral artery, was significantly lower on CE-MRA compared with TOF and CTA (P < 0.03). There was a significant correlation for the dimensional measurements of arterial diameters at CE-MRA with TOF (r = 0.88, 95% confidence interval 0.81-0.93), and CTA (r = 0.83, 95% confidence interval 0.73-0.90).

CONCLUSION

The described 3 T CE-MRA protocol, spanning from the cervical to the intracranial vessels, visualized and characterized the majority of intracranial arteries with image quality comparable with that obtained using TOF-MRA and CTA. Further clinical studies are required to establish the accuracy of the technique in a broader clinical setting.

Non-invasive detection of aortic and coronary atherosclerosis in homozygous familial hypercholesterolemia by 64 slice multi-detector row computed tomography angiography

Homozygous familial hypercholesterolemia (HoFH) is a rare disorder characterized by the early onset of atherosclerosis, often at the ostia of coronary arteries. In this study we document for the first time that aortic and coronary atherosclerosis can be detected using 64 slice multiple detector row computed tomographic coronary angiography (CTCA). We studied five HoFH patients (three females, two males, mean age 19.8+/-2.9 years, age range 15-23 years, with a mean low density lipoprotein (LDL) cholesterol 618+/-211 mg/dL) using 64 slice CTCA. None of the patients showed evidence of ischemia with standard exercise testing. Calcified and mixed atherosclerotic plaques adjacent to or compromising the coronary artery ostia were found in all study subjects. Coronary plaques causing significant obstruction were found in one patient, who had previously undergone coronary artery bypass surgery and aortic valve replacement. Two other patients were noted to have non-obstructive calcified, mixed and non-calcified coronary artery plaques. Our data suggest that CTCA could be a useful non-invasive method for detection of early aortic and coronary atherosclerosis specifically affecting the coronary ostia in HoFH subjects.

Accuracy of spiral CT in preoperative staging of gastric carcinoma: correlation with surgical and pathological findings

OBJECTIVE

To assess the accuracy of spiral CT scan in the preoperative staging of gastric carcinoma by comparing it with surgical/pathological staging.

MATERIAL AND METHOD

Twenty-eight patients with gastric carcinoma who underwent both preoperative CT scan and surgery were retrospectively studied for TNM classification. All CT scans were reviewed for tumor location, gastric wall thickness, tumor extension, N1 and N2 nodal involvement, and metastases to the liver, peritoneum and lung.

RESULTS

Spiral CT staging was correct in 20 of 28 patients (71.4%). The preoperative CT scan had 96.1% sensitivity, 100% specificity and 96.4% accuracy for evaluating serosal invasion. The sensitivity, specificity and accuracy for assessing pathologic lymph node involvement were 73.1, 50.0 and 84.2 percent, respectively. In the present study, peritoneal metastasis could not be identified by CT but CT had 100% sensitivity for evaluating hepatic metastases.

CONCLUSION

Spiral CT is a useful modality for preoperative staging of gastric carcinoma with high accuracy for evaluating serosal invasion and hepatic metastases.

Helical CT assessment on hilar cholangiocarcinoma: comparison value of arterial phase and portovenous phase correlation

OBJECTIVE

To study the correlation between the findings of hilar cholangiocarcinoma in hepatic arterial phase and portal venous phase. Attention will focus on whether the arterial phase imaging shows more detail than portal phase imaging.

MATERIAL AND METHOD

Descriptive study design with retrospective data collection in Srinagarind Hospital, Khon Kaen University. CT scans of the upper abdomen of 34 patients with pathologically proven hilar cholangiocarcinoma between 2002 and 2004 were reviewed for: (1) characteristic of the tumor; (2) adenopathy, (3) arterial involvement, (4) venous involvement, and (5) degree of biliary involvement on both the hepatic arterial and portal venous phases.

RESULTS

The correlation was high for characteristics of the tumor, the tumor enhancement pattern, and detection of adenopathy, degree of biliary involvement, and arterial involvement, but low for portal venous involvement which the portal venous phase detected better than the hepatic arterial phase.

CONCLUSION

In hilar type cholangiocarcinoma, the portal venous phase yielded the best findings. Furthermore, it showed all findings that were seen in the hepatic arterial phase. According to the present study, the authors suggest doing a pre-contrast study then a portal venous phase imaging for evaluation and diagnosis of hilar type cholangiocarcinoma. There is no necessity to perform hepatic arterial phase in hilar cholangiocarcinoma.

Retrospective evaluation of pediatric cranio-spinal axis irradiation plans with the Hi-ART tomotherapy system

Helical tomotherapy (HT) can be used for the delivery of cranio-spinal axis irradiation (CSAI) without the need for beam matching of conventional linac-based external beam irradiation. The aim of this study is to retrospectively evaluate HT plans used for treatment in nine patients treated with CSAI. Helical tomotherapy cranio-spinal axis irradiation (HT-CSAI) plans were created for each patient. Average length along the cranio-spinal axis of the PTV was 65.6 cm with a range between 53 and 74 cm. Treatment planning optimization and plan evaluation parameters were obtained from the HT planning station for each of the nine patients. PTV coverage by the 95% isodose surface ranged between 98.0 to 100.0% for all nine patients. The clinically acceptable dose variation within the PTV or tolerance range was between 0.7 and 2.5% for all nine patients. Doses to the organs at risk were clinically acceptable. An increasing length along the longitudinal axis of the PTV did not consistently increase the beam-on time indicating that using a larger jaw width had a greater impact on treatment time. With a larger jaw width it is possible to substantially reduce the normalized beam-on treatment time without compromising plan quality and sparing of organs at risk. By using a larger jaw width or lower modulation factor or both, normalized beam-on times were decreased by up to 61% as compared to the other evaluated treatment plans. From the nine cases reported in this study the minimum beam-on time was achieved with a jaw width of 5.0 cm, pitch of 0.287 and a modulation factor of 2.0. Large and long cylindrical volumes can be effectively treated with helical tomotherapy with both clinically acceptable dose distribution and beam-on time.

Spiral computed tomography for the diagnosis of acute pulmonary embolism

The accuracy of computed tomography (CT) imaging for the diagnosis of acute pulmonary embolism (PE) was reviewed. Single detector CT, based on pooled data, showed a sensitivity of 73% and multidetector CT, mostly 4-slice, showed a sensitivity of 83%. Respective specificities were 87% and 96%. Among patients with suspected PE evaluated with single slice CT, 20% of patients found to have venous thromboembolic disease were diagnosed on the basis of a positive CT venous phase venogram. With multislice CT, 14% were diagnosed on the basis of a positive CT venogram. The positive likelihood ratio with single detector CT was 5.7 and with multidetector CT it was 19.6. Respective negative likelihood ratios were 0.31 and 0.18. Calculations of post-test probability using pretest probability and likelihood ratios according to Bayes' theorem showed that even with multidetector CT, false positive and false negative images are not uncommon when clinical assessment is discordant with the CT interpretation. Outcome studies showed recurrent PE in only 1.7% or fewer untreated patients with negative CT pulmonary angiograms.

A cone-beam volume CT using a 3D angiography system with a flat panel detector of direct conversion type: usefulness for superselective intra-arterial chemotherapy for head and neck tumors

BACKGROUND AND PURPOSE

The development of flat panel detectors (FPDs) has made cone-beam CT feasible for practical use in a clinical setting. Our purpose was to assess the usefulness of cone-beam CT using the FPD in conjunction with conventional digital subtraction angiography (DSA) for performing superselective intra-arterial chemotherapy for head and neck tumors.

MATERIALS AND METHODS

Twenty-three consecutive patients (43 feeding arteries) were prospectively examined. All of the patients underwent intra-arterial rotational angiography using an FPD system, and the cone-beam CT was reconstructed from the volume dataset. Two radiologists evaluated the quality of the cone-beam CT and then evaluated whether the additional information provided by the cone-beam CT was useful for the interventional procedures.

RESULTS

In 41 (95%) of 43 arteries, the extent of contrast material perfusion was sufficiently visualized on cone-beam CT. In 20 (47%) of 43 arteries, the DSA plus cone-beam CT was superior to the DSA alone regarding the precise understanding of vascular territory of each artery. This information was helpful for predicting the drug delivery for superselective intra-arterial chemotherapy, especially in deeply invasive tumors with multiple feeding arteries.

CONCLUSION

In superselective intra-arterial chemotherapy for head and neck tumors, cone-beam CT with FPD provides useful additional information, which allows interventional radiologists to determine the feeders, as well as the dose of antitumor agent for each feeder.

GPU-based streaming architectures for fast cone-beam CT image reconstruction and demons deformable registration

This paper shows how to significantly accelerate cone-beam CT reconstruction and 3D deformable image registration using the stream-processing model. We describe data-parallel designs for the Feldkamp, Davis and Kress (FDK) reconstruction algorithm, and the demons deformable registration algorithm, suitable for use on a commodity graphics processing unit. The streaming versions of these algorithms are implemented using the Brook programming environment and executed on an NVidia 8800 GPU. Performance results using CT data of a preserved swine lung indicate that the GPU-based implementations of the FDK and demons algorithms achieve a substantial speedup--up to 80 times for FDK and 70 times for demons when compared to an optimized reference implementation on a 2.8 GHz Intel processor. In addition, the accuracy of the GPU-based implementations was found to be excellent. Compared with CPU-based implementations, the RMS differences were less than 0.1 Hounsfield unit for reconstruction and less than 0.1 mm for deformable registration.

A rebinned backprojection-filtration algorithm for image reconstruction in helical cone-beam CT

In the last few years, mathematically exact algorithms, including the backprojection-filtration (BPF) algorithm, have been developed for accurate image reconstruction in helical cone-beam CT. The BPF algorithm requires minimum data, and can reconstruct region-of-interest (ROI) images from data containing truncations. However, similar to other existing reconstruction algorithms for helical cone-beam CT, the BPF algorithm involves a backprojection with a spatially varying weighting factor, which is computationally demanding and, more importantly, can lead to undesirable numerical properties in reconstructed images. In this work, we develop a rebinned BPF algorithm in which the backprojection invokes no spatially varying weighting factor for accurate image reconstruction from helical cone-beam projections. This rebinned BPF algorithm is computationally more efficient and numerically more stable than the original BPF algorithm, while it also retains the nice properties of the original BPF algorithm such as minimum data requirement and ROI-image reconstruction from truncated data. We have also performed simulation studies to validate and evaluate the rebinned BPF algorithm.

Improvement in image quality of noncontrast head images in multidetector-row CT by volume helical scanning with a three-dimensional denoising filter

PURPOSE

The aim of this study was to improve the contrast-to-noise ratio on noncontrast head computed tomography (CT) images, which are crucial for assessing patients with acute ischemic stroke. We applied a technique combining volume helical scanning with a three-dimensional (3D) denoising filter.

MATERIALS AND METHODS

We scanned phantoms for low-contrast resolutions and helical/cone-beam artifacts as well as stroke patients using a 16-row multidetector-row CT (MDCT) unit. Volume helical scans with 1-mm collimation and nonhelical scans with 8-mm thickness were performed. From the 1-mm thick volume data, 8-mm thick contiguous images were generated before and after applying a 3D denoising filter.

RESULTS

On images stacked from volume data, the contrast-to-noise ratio was significantly improved by the 3D denoising filter and was nearly the same as that on nonhelical images. On stacked volume images, artifacts due to the cone beam and the helical scan were increased with larger helical pitches, but bone-related streak artifacts in the posterior fossa and underneath the calvarium were reduced when compared with nonhelical images.

CONCLUSION

Volume helical scan with a 3D denoising filter effectively improves image quality in noncontrast head MDCT images.

A new scheme for view-dependent data differentiation in fan-beam and cone-beam computed tomography

In computed tomography, analytical fan-beam (FB) and cone-beam (CB) image reconstruction often involves a view-dependent data differentiation. The implementation of this differentiation step is critical in terms of resolution and image quality. In this work, we present a new differentiation scheme that is robust to changes in the data acquisition geometry and to coarse view sampling. Our scheme was compared to two previously suggested methods, which we call the direct scheme and the chain-rule scheme. Image reconstructions were performed from computer-simulated data of the Shepp-Logan phantom, the FORBILD thorax phantom and a modified FORBILD head phantom. For FB reconstruction, we investigated three acquisition geometries: a circular, an ellipse-shaped and a square-shaped trajectory. For CB reconstruction, the circle-plus-line trajectory was considered. Image comparison showed that the new scheme performs consistently well when varying the scenario, in both FB and CB geometry, unlike the other two schemes.

Reduction of Artifacts Induced by Misaligned Geometry in Cone-Beam CT

The quality of computed tomography (CT) images frequently suffers from artifacts caused by scanner misalignments. In this paper, we discuss the results of our improved approximate cone-beam reconstruction formula, which corrects for the mechanical misalignment of the scanner. Based on the general filtered back-projection (FBP) algorithm proposed by Feldkamp, the new formula reduces the artifacts in reconstructed images. Six parameters are employed to describe the scanner misalignment. Experimental results show that the images reconstructed by using the new formula are clearer than those reconstructed by using the general FBP algorithm in a misaligned system. Through the new formula, we have reduced the artifacts caused by misalignment.

Mass screening of multiple abdominal solid organs using mobile helical computed tomography scanner--a preliminary report

OBJECTIVE

The possibility of a new screening procedure for multiple abdominal solid organs using a mobile helical computed tomography (CT) scanner was evaluated.

METHODS

A total of 4,543 residents, who were 40 years of age or older, received CT scanning without contrast medium. The mean age of participants was 64 years including 2,022 males and 2,521 females.

RESULTS

A total of 2,105 abnormal findings were uniquely detected in 1,594 participants. Liver and kidney diseases including ureter occupied around 30% of total abnormal findings, respectively. Besides frequent cystic or calcified lesions, solid tumours were suspected in 56 lesions, which received further examination by specialized physicians. Five (9%) of them were confirmed as being malignant tumours including pancreatic cancer in two patients, and liver, lung and ovary cancers in one patient each, respectively. All five patients with each malignant lesion received curative operations. Small-sized abdominal aortic aneurysms and heart valve diseases were uniquely found in 22 and two patients, respectively.

CONCLUSION

Qualitative diagnoses of solid tumours were difficult using CT findings without contrast medium. CT screening procedures require further investigation in aspect of the selection of examinees, CT scanning procedure, sensitivity and specificity, and cost-effectiveness.

Commissioning experience with cone-beam computed tomography for image-guided radiation therapy

This paper reports on the commissioning of an Elekta cone‐beam computed tomography (CT) system at one of the first U.S. sites to install a “regular,” off‐the‐shelf Elekta Synergy (Elekta, Stockholm, Sweden) accelerator system. We present the quality assurance (QA) procedure as a guide for other users. The commissioning had six elements: (1) system safety, (2) geometric accuracy (agreement of megavoltage and kilovoltage beam isocenters), (3) image quality, (4) registration and correction accuracy, (5) dose to patient and dosimetric stability, and (6) QA procedures. The system passed the safety tests, and agreement of the isocenters was found to be within 1 mm. Using a precisely moved skull phantom, the reconstruction and alignment algorithm was found to be accurate within 1 mm and 1 degree in each dimension. Of 12 measurement points spanning a 9×9×15‐cm volume in a Rando phantom (The Phantom Laboratory, Salem, NY), the average agreement in the x, y, and z coordinates was 0.10 mm, −0.12 mm, and 0.22 mm [standard deviations (SDs): 0.21 mm, 0.55 mm, 0.21 mm; largest deviations: 0.6 mm, 1.0 mm, 0.5 mm] respectively. The larger deviation for the y component can be partly attributed to the CT slice thickness of 1 mm in that direction. Dose to the patient depends on the machine settings and patient geometry. To monitor dose consistency, air kerma (output) and half‐value layer (beam quality) are measured for a typical clinical setting. Air kerma was 6.3 cGy (120 kVp, 40 mA, 40 ms per frame, 360‐degree scan, S20 field of view); half value layer was 7.1 mm aluminum (120 kV, 40 mA).

We suggest performing items 1, 2, and 3 monthly, and 4 and 5 annually. In addition, we devised a daily QA procedure to verify agreement of the megavoltage and kilovoltage isocenters using a simple phantom containing three small steel balls. The frequency of all checks will be reevaluated based on data collected during about 1 year.

PACS number: 87.53.Xd

[Dual-source CT coronary angiography]

Multidetector computed tomography (MDCT) has been demonstrated to be a very useful technique to non-invasively study coronary arteries. Despite the high spatial and temporal resolution of 64-slice MDCT scanners, this technique has several limitations. Dual-source computed tomography (DSCT) allows to study coronary arteries with excellent diagnostic quality in all subjects independent of the heart rate, thus avoiding the use of beta-blockers. In this article DSCT studies from three subjects with elevated heart rate and irregular heart rhythm are described. Usefulness of this technique to obtain studies of excellent quality in cases in which conventional 64-row-MDCT might present limitations is emphasized.

Evaluation of Coronary Stents and Stenoses at Different Heart Rates With Dual Source Spiral CT (DSCT)

OBJECTIVES

Evaluation of coronary arteries at higher heart rates and in the presence of coronary stents remains problematic. The utilization of dual source computed tomography (DSCT) might improve the visualization of the coronary arteries under these conditions by imaging at a temporal resolution of 83 milliseconds, independent of heart rate.

MATERIALS AND METHODS

Vessel phantoms (diameter 2-4 mm) were attached to a robotic device to simulate cardiac motion and scanned with a DSCT system. The phantoms had either inserts leading to 50% stenosis or carried stents. Images were evaluated for motion artifacts and measurements of the normal, stenotic, and in-stent lumen at different heart rates (50-120 bpm) were performed. Quantile regression analysis was performed to investigate heart rate dependence of the measurement errors.

RESULTS

Visualization of the stenoses and stents was possible without motion artifacts at heart rates of up to 120 bpm. Image quality was similar for the static (0 bpm) and the dynamic (50-120 bpm) scans. Errors for diameter measurements of the vessel lumen and the stenotic lumen were low (3-mm vessel: 1-2%), but considerable for in-stent diameter measurements (3-mm stent: 27-32%). A window/level setting of 1500/300 Hounsfield units was more favorable for stent evaluation. No heart rate dependence was found.

CONCLUSIONS

Depiction of coronary stents with DSCT is possible across a large range of simulated heart rates without motion artifacts and with image quality superior to that of previous generations of CT scanners.