[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.