Three-dimensional volumetric display of CT data: effect of scan parameters upon image quality

Technological developments of X-ray computed tomography over half a century: User's influence on protocol optimization

Since the introduction of Computed Tomography (CT), technological improvements have been impressive. At the same time, the number of adjustable acquisition and reconstruction parameters has increased substantially. Overall, these developments led to improved image quality at a reduced radiation dose. However, many parameters are interrelated and part of automated algorithms. This makes it more complicated to adjust them individually and more difficult to comprehend their influence on CT protocol adjustments. Moreover, the user's influence in adapting protocol parameters is sometimes limited by the manufacturer's policy or the user's knowledge. As a consequence, optimization can be a challenge. A literature search in Embase, Medline, Cochrane, and Web of Science was performed. The literature was reviewed with the objective to collect information regarding technological developments in CT over the past five decades and the role of the associated acquisition and reconstruction parameters in the optimization process.

Is expansion thoracoplasty a safe procedure for mobility and growth potential of the spine? Spontaneous fusion after multiple chest distractions in young children

BACKGROUND

Expansion thoracoplasty (ET) is claimed to be a spine-sparing procedure because of the fact that the spine is not exposed directly and intervention toward the spinal column is not performed. It is also recommended in cases of primary spine deformities without rib fusion/aplasia and when the primary problem is not in the thorax itself. The aim of this study was to report spontaneous spinal fusion after multiple thoracic distractions in patients with congenital thoracospinal deformities who have undergone ET in early childhood.

METHODS

In our clinic, between May 2003 and March 2010, ET treatment was started in 11 patients who had congenital spinal deformity along with thoracic asymmetry due to fused ribs. The lengthening procedures for 6 of them are still ongoing. This study includes 5 of these patients who had undergone 3-dimensional computed tomography (3D-CT) scans. Four of these patients underwent a CT scan as part of the graduation protocol and 1 was ordered a 3D-CT because a newly formed bony fusion of the ribs was observed in a lengthening procedure.

RESULTS

The mean age of the patients (4 F, 1 M) was 4.2 years (range, 2 to 8 y) at the time of the index operation. The mean number of lengthening procedures was 9.4 (range, 7 to 13). The mean follow-up period was 73 months (range, 60 to 96 mo). All 5 patients in the latest follow-up were evaluated by x-ray and 3D-CT scans of the whole spine. The CT scans confirmed spontaneous spinal fusion in the thoracic spine.

CONCLUSIONS

We speculate that distraction-based, growth-friendly instrumentations are not risk-free for spinal health and motion, even when the instrumentation is not primarily on the spine.

LEVEL OF EVIDENCE

Level IV.

Development of a simulation system in mandibular orthognathic surgery based on integrated three-dimensional data

Purpose

Surgical simulation should reflect the 3D movement of dentition and the resultant movement of the osteotomized segments, which can influence surgical outcome. The present study was aimed at developing a new simulation system that enables virtual osteotomy of a given surgical situation and evaluation of the bony interference between the osteotomized segments of the mandible.

Subjects and methods

The data of 3D computer tomography (CT) for maxillomandibular dental casts were integrated into the standard coordinates of a 3D cephalogram. To evaluate the accuracy of the system, measurement errors of the 3D CT virtual model from a dry skull were compared with the computer simulation system and a contact-type 3D digitizer. To examine the clinical accessibility, 15 mandibular prognathism patients with mild to severe asymmetry were evaluated with the simulation program.

Results

The average error of measurement in all directions was 1.31 mm. It was possible to simulate various osteotomy procedures by conversion of the 3D coordinates of the dental cast and CT data into the standard coordinate system of a 3D cephalogram. Using this simulation system, it was possible to prevent condylar torque or segment malpositioning by removing the bony interference visualized by a 3D virtual model.

Conclusion

A new system, which enables the precise visualization of osteotomized segments and calculation of bony interference, was proposed in the present study. This new system provides an acceptable precision of treatment planning of orthognathic surgery, especially for facial asymmetry.

Computer-assisted pelvic tumor resection: fields of application, limits, and perspectives

The treatment of malignant tumors involving the pelvic area is a challenging problem in musculoskeletal oncology due to the complex pelvic anatomy and the often large tumor size at presentation. The use of navigation systems has effectively increased surgical precision aiming at optimal preservation of pelvic structures without compromising oncologic outcome by means of improved visibility of the surgical field, and enabling intraoperative display and 3D reproduction of preoperatively determined pelvic osteotomy and resection levels. In the following sections, current developments in computer-assisted pelvic surgery are reviewed and possible fields of application, as well as limitations of navigation systems, are discussed.

Real-time stereographic rendering and display of medical images with programmable GPUs

The study was to explore the power and feasibility of using programmable graphics processing units (GPUs) for real-time rendering and displaying large 3D medical datasets for stereoscopic display workstation. Lung cancer screening CT images were used for developing GPU-based stereo rendering and displaying. The study was run on a personal computer with a 128 MB NVIDIA Quadro FX 1100 graphics card. The performance of rendering and displaying was measured and compared between GPU-based and central processing unit (CPU)-based programming. The results indicate that GPU-based programming was capable of rendering large 3D datasets at real-time interactive rates with stereographic displays.

Validation of computed tomography protocols for simulated mandibular lesions: a comparison study

Computed tomography is the choice technique to assess oral and maxillofacial osseous lesions because it provides hard and soft tissues visualization in one examination without superimposition of surrounding structures. This examination offers a significant advance in maxillofacial lesions detection with an excellent anatomic resolution. The aim of this research was to evaluate the validity of two protocols, in axial sections, in simulated mandibular lesions. Two CT protocols were obtained in dry mandibles in which perforations were done simulating lesions. Two observers, previously calibrated, evaluated the images according to different parameters. The results indicated that the sensitivity and specificity in lesion detection were 100% for both protocols, but the detection of loci number of multilocular lesions and the location and detection of medullar invasion obtained reduced validity values, which were influenced by the acquisition protocol. We concluded that thinner axial slices and reconstructions were more effective in detecting early medullar invasion and loci number. Thicker protocols were not considered appropriate to detect multilocular lesions and early stages of medullar invasion.

Role of image fusion combining three-dimensional digital subtraction angiography with magnetic resonance imaging in evaluation of unruptured cerebral aneurysms

OBJECTIVES

The goal of this study was to evaluate the usefulness of a recently developed image fusion of three-dimensional digital subtraction angiography (3D DSA) and magnetic resonance (MR) images, DSA-MR fusion, in the pre-treatment assessment of cerebral aneurysm.

METHODS

Eighteen patients with 21 unruptured anterior or posterior circulation aneurysms underwent pre-treatment DSA-MR fusion. The authors independently assessed whether DSA-MR fusion images provided any useful additional information compared with analysing 3D DSA and MR images separately, and if this had an impact on the therapeutic decision-making of unruptured aneurysms.

RESULTS

DSA-MR fusion images were obtained within 30 minutes for all patients. In 19 of 21 aneurysms, it provided the following additional information to the findings of 3D DSA, MR images or both: the passing course in the brain tissues of perforating arteries near or originating from an aneurysm, and/or the spatial relationship between an aneurysm and an oculomotor nerve. This information from DSA-MR fusion images was useful for diagnosis, therapeutic decision-making and the risk assessment associated with the treatment, as well as patient education regarding cerebral aneurysm.

DISCUSSION

DSA-MR fusion images were useful for the pre-treatment evaluation of unruptured cerebral aneurysms as a supplement to DSA and MR images.

Informatics in radiology (infoRAD): introduction to the language of three-dimensional imaging with multidetector CT

The recent proliferation of multi-detector row computed tomography (CT) has led to an increase in the creation and interpretation of images in planes other than the traditional axial plane. Powerful three-dimensional (3D) applications improve the utility of detailed CT data but also create confusion among radiologists, technologists, and referring clinicians when trying to describe a particular method or type of image. Designing examination protocols that optimize data quality and radiation dose to the patient requires familiarity with the concepts of beam collimation and section collimation as they apply to multi-detector row CT. A basic understanding of the time-limited nature of projection data and the need for thin-section axial reconstruction for 3D applications is necessary to use the available data effectively in clinical practice. The axial reconstruction data can be used to create nonaxial two-dimensional images by means of multiplanar reformation. Multiplanar images can be thickened into slabs with projectional techniques such as average, maximum, and minimum intensity projection; ray sum; and volume rendering. By assigning a full spectrum of opacity values and applying color to the tissue classification system, volume rendering provides a robust and versatile data set for advanced imaging applications.

Multi-detector row CT scanning in Paleoanthropology at various tube current settings and scanning mode

The purpose of this study was to determine the optimal tube current setting and scanning mode for hominid fossil skull scanning, using multi-detector row computed tomography (CT). Four fossil skulls (La Ferrassie 1, Abri Pataud 1, CroMagnon 2 and Cro-Magnon 3) were examined by using the CT scanner LightSpeed 16 (General Electric Medical Systems) with varying dose per section (160, 250, and 300 mAs) and scanning mode (helical and conventional). Image quality of two-dimensional (2D) multiplanar reconstructions, three-dimensional (3D) reconstructions and native images was assessed by four reviewers using a four-point grading scale. An ANOVA (analysis of variance) model was used to compare the mean score for each sequence and the overall mean score according to the levels of the scanning parameters. Compared with helical CT (mean score=12.03), the conventional technique showed sustained poor image quality (mean score=4.17). With the helical mode, we observed a better image quality at 300 mAs than at 160 in the 3D sequences (P=0.03). Whereas in native images, a reduction in the effective tube current induced no degradation in image quality (P=0.05). Our study suggests a standardized protocol for fossil scanning with a 16 x 0.625 detector configuration, a 10 mm beam collimation, a 0.562:1 acquisition mode, a 0.625/0.4 mm slice thickness/reconstruction interval, a pitch of 5.62, 120 kV and 300 mAs especially when a 3D study is required.

Assessment of real-time 3D visualization for cardiothoracic diagnostic evaluation and surgery planning

RATIONALE AND OBJECTIVES

Three-dimensional (3D) real-time volume rendering has demonstrated improvements in clinical care for several areas of radiological imaging. We test whether advanced real-time rendering techniques combined with an effective user interface will allow radiologists and surgeons to improve their performance for cardiothoracic surgery planning and diagnostic evaluation.

MATERIAL AND METHODS

An interactive combination 3D and 2D visualization system developed at the University of North Carolina at Chapel Hill was compared against standard tiled 2D slice presentation on a viewbox. The system was evaluated for 23 complex cardiothoracic computed tomographic (CT) cases including heart-lung and lung transplantation, tumor resection, airway stent placement, repair of congenital heart defects, aortic aneurysm repair, and resection of pulmonary arteriovenous malformation. Radiologists and surgeons recorded their impressions with and without the use of the interactive visualization system.

RESULTS

The cardiothoracic surgeons reported positive benefits to using the 3D visualizations. The addition of the 3D visualization changed the surgical plan (65% of cases), increased the surgeon's confidence (on average 40% per case), and correlated well with the anatomy found at surgery (95% of cases). The radiologists reported fewer and less major changes than the surgeons in their understanding of the case due to the 3D visualization. They found new findings or additional information about existing findings in 66% of the cases; however, they changed their radiology report in only 14% of the cases.

CONCLUSION

With the appropriate choice of 3D real-time volume rendering and a well-designed user interface, both surgeons and radiologists benefit from viewing an interactive 3D visualization in addition to 2D images for surgery planning and diagnostic evaluation of complex cardiothoracic cases. This study finds that 3D visualization is especially helpful to the surgeon in understanding the case, and in communicating and planning the surgery. These results suggest that including real-time 3D visualization would be of clinical benefit for complex cardiothoracic CT cases.

Comparison of Accuracy of Three-Dimensional Spiral Computed Tomography, Standard Radiography, and Direct Measurements in Evaluating Facial Fracture Healing in a Rat Model

Complex maxillofacial fractures demand a detailed understanding of the three-dimensional (3D) pattern of injury. Evaluation of the outcome of the facial fracture repair additionally requires optimal demonstration of fracture gap, bony union, fibrous callus or incorporation of fracture ends, presence of incomplete fusion, or pseudoarthrosis. Although 3D computed tomography (CT) is reliably used for the diagnosis of complex facial fractures, its value in facial fracture healing is unknown. An experimental study was conducted to determine the accuracy of 3D spiral CT scans in evaluating facial fracture healing during the early and late postoperative periods. In 10 adult Wistar Albino rats, a standardized bone defect (3 mm) was created within the mid portion of each zygomatic arch (n = 20). At 10 and 20 weeks postfracture, gap distance displayed by 3D CT and plane radiography (posteroanterior) were measured. At 20 weeks postfracture, intraoperative measurement was also performed. A comparison between 3D CT, radiography, and intraoperative findings was performed. At 10 weeks postfracture, the fracture sites displayed larger bone defects in imaging with 3D CT than with plane radiography. The difference between groups was statistically significant (P < 0.05). The mean defect size imaged by 3D CT was 0.91 +/- 0.82 mm (standard deviation) and by plane radiography was 0.42 +/- 0.16 mm. At 20 weeks postfracture, the mean defect size imaged by 3D CT was 0.56 +/- 0.64 mm, and by plane radiography was 0.38 +/- 0.22 mm. The difference between groups was not statistically significant (P > 0.05). The defect size imaged by both plane radiography and 3D CT was significantly less than the measurement obtained from the intraoperative assessment (P < 0.05). It was concluded that 3D CT has limited benefit in the detection of newly formed bone at week 10 and in the detection of fibrous callus, which can eventually give rise to the bony tissue. Plane radiography is more valid during the early postoperative period (week 10), because it can detect the fibrous callus and newly formed bone more precisely. Gap distance between fracture ends could be determined by 3D CT accurately at week 20, although there was a tendency, which was not statistically significant, to overestimate the amount of bone defect measured by 3D CT when compared with that of plane radiography.

Computed tomography-based navigation for hip, knee, and spine surgery

A review of CT-based orthopaedic navigation is presented with a specific emphasis on arthroplasty for the hip and the knee. Fundamental issues about the laboratory and clinical validation of the applications are addressed. The ability to compute the position and orientation of an acetabular implant using a postoperative CT scan was investigated. Angle deviations relative to known positions were computed with an error of less than 1 degree. Then, the system accuracy for three-dimensional reconstruction and registration of two cadaveric pelvis specimens was measured with more than 350 registrations. We observed a maximal inclination error of 5 degrees in 99% of cases and a maximal anteversion error of 5 degrees in 97% of cases. The accuracy of the three-dimensional reconstruction and registration for knee arthroplasty also was measured and computed with an angular accuracy of 0.5 degrees in the AP plane and accuracy of 3 degrees in the lateral plane. A clinical study then was done in 109 cases where 96% of implants were installed with a hip-knee-ankle angle of 180 +/- 3 degrees . Computed tomography-based navigation for orthopaedic surgery provides greater accuracy and reproducibility than conventional surgery. As noted by learning curves, software improvements are needed to bring it into daily clinical routine.

The use of medical imaging-based kinematic analysis in the evaluation of wrist function and outcome

The authors developed a 3D CT technique to analyze in vivo variations in carpal bone position based on 3D reconstruction of transverse CT data in 5 wrist positions. The subject groups analyzed consisted of 40 asymptomatic volunteers and 30 patients with various wrist disorders (fractures, instabilities). In 11 anatomic specimens, this kinematic analysis was completed by a radiographic morphologic study and an investigation of capsular ligament anatomy. Clinical applications showed that carpal bone motion in the injured wrist was not significantly different from contralateral, asymptomatic wrist motion. In both wrists of patients with unilateral pathology, however, significant differences were observed as compared with asymptomatic volunteers. Scaphoid motion was bilaterally altered, suggesting the existence of anatomic or kinematic factors predisposing to certain carpal pathologies.

Bone induction capacity of the periosteum and neonatal dura in the setting of the rat zygomatic arch fracture model

OBJECTIVES

Osteogenic properties of the dura and periosteum are thought to contribute to the regenerative capacity of membranous bone tissue. The purpose of this investigation was to elucidate (1) whether dura without underlying neural tissues can induce osteogenesis, (2) to what extent the periosteum participates in membranous bone healing, and (3) the difference between dura-induced and periosteum-induced osteogenesis.

METHODS

A standardized 2-mm defect was created within the middle portion of each zygomatic arch in 30 Wistar albino rats. The rats were divided into 3 groups, 10 animals in each group. In group 1, the periosteum was removed and neonatal dura grafts were transplanted onto the zygomatic arch bone defect circumferentially. In group 2, the overlying periosteum was preserved. In group 3, the periosteum was removed. At 3 and 10 weeks, animals from each group were killed, and specimens were obtained. Data were collected from the 3-dimensional computed tomographic scans and histologic studies to compare the extent of bony repair.

RESULTS

Fracture sites demonstrated osteogenesis associated with chondrogenesis in groups 1 and 2 and only limited osteogenesis with no chondrogenesis in group 3. In some animals in group 3, cortical bone ends underwent resorption. In groups 1 and 2, bone defects were obliterated by the formation of the mature compact bone at 10 weeks postoperatively. The difference between bone regeneration in these groups was not significant (P =.16). In group 3, the defects failed to heal by bony union, and in most of the samples the fibrous union was observed instead. The difference between groups 1 and 3 was significant (P =.03). The difference between groups 2 and 3 was not significant (P =.09).

CONCLUSIONS

The trend toward significance is in agreement with the current clinical practice of preserving periosteum in the manipulations of the membranous bone defects. Newborn dura can exert a potentiating effect on osteogenesis.

Diagnosis of a porto-azygous shunt using helical computed tomography angiography

Congenital portosystemic shunts occur uncommonly in dogs. Conventional diagnostic methods either do not offer simultaneous diagnosis and anatomic characterization or require an invasive selective catheterization. Helical computed tomography (HCT) is a rapid, noninvasive means of acquiring cross-sectional images of any portion of the body. Combined with a peripheral venous injection of contrast medium, HCT can produce computer-rendered, "angiogram-like" images of vasculature. These computer-generated multiplanar and three-dimensional HCT angiographic images were helpful in the diagnosis and accurate anatomic characterization of a porto-azygous shunt. A brief discussion of scanner and contrast medium protocol considerations necessary to achieve adequate vascular opacification for volumetric data reconstructions and diagnosis are outlined.

Multiplanar reformat display technique in abdominal multidetector row CT imaging

The purpose of this study was to evaluate the image quality and diagnostic value of multiplanar reformat (MPR) of abdominal CT performed with multidetector row spiral technique (MDCT). Forty-five patients were referred for an abdominal MDCT angiography. No significant differences in image quality and in the number of lesions detected were found between axial and MPR images (t-test, P>.90 and chi-square, P>.95). Additional diagnostic value to axial images could be obtained with MPR display.

Recent development on computer aided tissue engineering--a review

The utilization of computer-aided technologies in tissue engineering has evolved in the development of a new field of computer-aided tissue engineering (CATE). This article reviews recent development and application of enabling computer technology, imaging technology, computer-aided design and computer-aided manufacturing (CAD and CAM), and rapid prototyping (RP) technology in tissue engineering, particularly, in computer-aided tissue anatomical modeling, three-dimensional (3-D) anatomy visualization and 3-D reconstruction, CAD-based anatomical modeling, computer-aided tissue classification, computer-aided tissue implantation and prototype modeling assisted surgical planning and reconstruction.

The quality of reconstructed 3D images in multidetector-row helical CT: experimental study involving scan parameters

OBJECTIVE

To determine which multidetector-row helical CT scanning technique provides the best-quality reconstructed 3D images, and to assess differences in image quality according to the levels of the scanning parameters used.

MATERIALS AND METHODS

Four objects with different surfaces and contours were scanned using multidetector-row helical CT at three detector-row collimations (1.25, 2.50, 5.00 mm), two pitches (3.0, 6.0), and three different degrees of overlap between the reconstructed slices (0%, 25%, 50%). Reconstructed 3D images of the resulting 72 sets of data were produced using volumetric rendering. The 72 images were graded on a scale from 1 (worst) to 5 (best) for each of four rating criteria, giving a mean score for each criterion and an overall mean score. Statistical analysis was used to assess differences in image quality according to scanning parameter levels.

RESULTS

The mean score for each rating criterion, and the overall mean score, varied significantly according to the scanning parameter levels used. With regard to detector-row collimation and pitch, all levels of scanning parameters gave rise to significant differences, while in the degree of overlap of reconstructed slices, there were significant differences between overlap of 0% and of 50% in all levels of scanning parameters, and between overlap of 25% and of 50% in overall accuracy and overall mean score. Among the 18 scanning sequences, the highest score (4.94) was achieved with 1.25 mm detector-row collimation, 3.0 pitch, and 50% overlap between reconstructed slices.

CONCLUSION

Comparison of the quality of reconstructed 3D images obtained using multidetector-row helical CT and various scanning techniques indicated that the 1.25 mm, 3.0, 50% scanning sequence was best. Quality improved as detector-row collimation decreased; as pitch was reduced from 6.0 to 3.0; and as overlap between reconstructed slices increased.

Dual-slice helical CT of the thoracic aorta

With the advent of helical CT, the capability of noninvasive imaging of the thoracic aorta has been enhanced considerably. In this article, we describe the potential of helical CT using dual-slice technology to evaluate thoracic aortic diseases such dissection, aneurysm, trauma, infection, inflammation, thromboembolic disease, and postoperative complications. Technical considerations for optimal CT imaging as well as limitations of helical CT are highlighted.

Three-dimensional volume rendering of spiral CT data: theory and method

Three-dimensional (3D) medical images of computed tomographic (CT) data sets can be generated with a variety of computer algorithms. The three most commonly used techniques are shaded surface display, maximum intensity projection, and, more recently, 3D volume rendering. Implementation of 3D volume rendering involves volume data management, which relates to operations including acquisition, resampling, and editing of the data set; rendering parameters including window width and level, opacity, brightness, and percentage classification; and image display, which comprises techniques such as "fly-through" and "fly-around," multiple-view display, obscured structure and shading depth cues, and kinetic and stereo depth cues. An understanding of both the theory and method of 3D volume rendering is essential for accurate evaluation of the resulting images. Three-dimensional volume rendering is useful in a wide variety of applications but is just now being incorporated into commercially available software packages for medical imaging. Although further research is needed to determine the efficacy of 3D volume rendering in clinical applications, with wider availability and improved cost-to-performance ratios in computing, 3D volume rendering is likely to enjoy widespread acceptance in the medical community.

Dual-phase spiral CT angiography with volumetric 3D rendering for preoperative liver transplant evaluation: preliminary observations

PURPOSE

The goal of our study was to determine whether dual-phase spiral CT angiography with 3D volume rendering could be used for preoperative evaluation and patient selection for orthotopic liver transplantation candidates.

METHOD

Fifty consecutive potential candidates for liver transplantation were evaluated with dual-phase spiral CT with 3D volume rendering. Intravenous contrast medium was administered as bolus peripheral injection at 3 ml/s. The protocol consisted of a contrast-enhanced dual-phase spiral CT (arterial phase acquisition at 30 s after initiation of contrast medium injection followed by portal venous phase beginning at 60 s) with scan parameters of 0.75 s gantry rotation speed, 3 mm collimation, 5 to 6 mm/s table speed, and reconstruction at 1 mm intervals for arterial-phase images and 3 mm collimation for portal venous-phase studies (Siemens Plus 4 scanner; Siemens Medical Systems, Iselin, NJ, U.S.A.). All scan information was sent to a free-standing workstation (Silicon Graphics Onyx or Infinite Reality, Mountain View, CA, U.S.A.) for interactive real-time 3D volume rendering using a customized version of the Volren volume renderer (Silicon Graphics; Advanced Imaging Laboratory, Johns Hopkins Medical Institutions, Baltimore, MD, U.S.A.). The arterial phase was used to create vascular maps of the celiac axis including the origin(s) of the hepatic artery and origin of the superior mesenteric artery. The portal phase was used to define portal venous patency as well as the hepatic venous anatomy. All images were analyzed for vascular patency, shunting, or collateralization as well as the status of the underlying liver (i.e., liver size, cirrhosis, tumor, etc.).

RESULTS

All 50 studies were successfully completed without complication. The 3D CT angiograms defined key arterial and venous structures including origin(s) of the hepatic artery, portal vein and/or superior mesenteric vein thrombosis, cavernous transformation of the portal vein, and/or other collateral vasculature. Ten patients (20%) demonstrated anomalous anatomy at the origin(s) of the hepatic artery. Portal vein thrombosis with cavernous transformation of the portal vein was shown in six patients, and there were three cases of partial venous thrombosis. Underlying liver tumors as well as parenchymal liver disease were well defined. Hepatic masses were found in five patients. Masses were pathologically proven as hepatocellular carcinoma (n = 1), giant cavernous hemangioma (n = 1), hepatic adenoma (n = 1), and focal nodular hyperplasia (n = 2).

CONCLUSION

Preliminary results suggest that dual-phase spiral CT with CT angiography can provide a comprehensive preoperative liver transplant evaluation, supplying the necessary information for patient selection and surgical planning. As a single, minimally invasive examination, this should significantly impact patient care by minimizing procedures and avoiding potential complications.

Increasing spiral CT benefits with postprocessing applications

This paper reviews the current and future role of various postprocessing tools for epidemiologically important diseases. It introduces a generic business system for diagnosis and treatment using Spiral CT. Postprocessing of Spiral CT data should become a routine part of radiological practice. As viewing moves from film to monitor displays, interactive postprocessing tools support evaluation of CT studies and will in some cases also improve diagnostic accuracy. Track-ball controlled browsing through the volume data may be performed on axial images or on multiplanar reformats (MPR). These tools can be expected to become an integral part of most CT evaluations in the near future. Already now, MPR are important adjuncts for most orthopaedic applications. Presently, three-dimensional (3D) displays are used mainly in orthopaedic and trauma patients. In CT angiography, 3D surface displays and maximum intensity projections are routine display modalities. New volume rendering techniques (VRT) with interactive parameter changes will make 3D imaging of soft tissues feasible as well. The key input factor for many postprocessing applications will be Spiral CT data sets with high z-axis resolution (subsecond scanning, thin collimation, overlapping image reconstruction) and optimised application of contrast media. The most important benefit of postprocessing is the communication with the referring physician since 3D representations are becoming increasingly important for treatment planning and control. Postprocessing services will become a key ingredient of a successful radiological practice. If radiology does not provide it, the other physicians will do it themselves. For treatment simulation, virtual surgical instruments and tissue motion models are still in their infancy and will keep software architects and physicians busy for the next decade of Spiral-CT.

The use of spiral computed tomography in musculoskeletal radiology of the lower limb: the calcaneus as an example

The advent of spiral (helical) computed tomography (CT) has markedly increased the speed of modern CT systems and has found a use in a variety of musculoskeletal applications. However, the limitations of the technique must be understood if examinations are to be tailored and optimised. This review puts the limitations and advantages into context by outlining how spiral CT can be applied to musculoskeletal imaging of the lower limb. Imaging of intra-articular fractures of the calcaneus serves as a timely example of how the imaging parameters can be optimised and where the technique can offer potential advantages over conventional CT.

Segmentation of the visible human for high-quality volume-based visualization

This article describes a combination of interactive classification and super-sampling visualization algorithms that greatly enhances the realism of 3-D reconstructions of the Visible Human data sets. Objects are classified on the basis of ellipsoidal regions in RGB space. The ellipsoids are used for super-sampling in the visualization process.

Three-dimensional computed tomographic imaging in the diagnosis of vertebral column trauma: experience based on 21 patients and review of the literature

OBJECTIVE

To compare standard x-ray films, two-dimensional computed tomographic reconstructions and three-dimensional (3-D) computed tomographic reconstructions for assessing the grade, extent, and severity of vertebral fracture.

PATIENTS AND METHODS

3-D images were created from standard computed tomographic scans obtained using a General Electric PACE scanner. In 21 patients (17 men and four women) these images were obtained during both the acute phase and at long-term follow-up; there were six cervical, four dorsal, five dorso-lumbar, and six lumbar fractures.

RESULTS

The 3-D images supplied useful information in complex traumas with rotation and/or dislocation of the vertebral body and in cases with loss of spinal alignment. The 3-D images also proved to be useful as an adjunctive imaging method for evaluation of bone fusion integrity.

CONCLUSION

3-D images produced by recently available software provide a 3-D understanding much more readily than do multiple two-dimensional images. Because it would be very difficult to standardize this method of imaging, it seems best that the specialist (orthopedic surgeon, neurosurgeon, neuroradiologist) be present during the investigation to decide the viewing angles. An important limitation to this method is the presence of degenerative disease or osteoporosis, mainly in elderly patients.

Multiplanar image reconstruction and 3D imaging using a musculoskeletal phantom: conventional versus helical CT

PURPOSE

Our goal was to perform a detailed comparison of the relative performances of helical CT (pitches 1.0, 1.5, and 2.0) and conventional (overlapped and nonoverlapped) CT in detailed 3D and MPR musculoskeletal imaging.

METHOD

A specially designed bone fragment phantom was imaged with multiple slice thicknesses using conventional (overlapped and nonoverlapped) and helical (varying pitch and slice index) CT. Studies were randomized, blinded, and graded using predetermined criteria by 10 radiologists. Statistical analysis included an assessment of raw image scores, a separate testing using duplicate copies of the conventional images as gold standards, and a multivariate model based upon the results of both scoring systems.

RESULTS

When assessing raw scores of the images, conventional scans were consistently scored more favorably than helical studies. Decreasing the slice index improved conventional CT studies and helical studies with a pitch of 1.0, but showed no effect on helical studies with a pitch of > 1.0. When using the conventional studies as gold standards, the helical studies were consistently graded as poorer than conventional overlapped and nonoverlapped studies.

CONCLUSION

For detailed musculoskeletal 3D and MPR work, helical CT may not adequately compare with conventional CT and offers no discernible advantage, particularly for pitches of > 1.0.

The accuracy of measurements of three-dimensional computed tomography reconstructions

PURPOSE

The purpose of this study was to evaluate the accuracy and reproducibility of linear measurements obtained from three-dimensional reconstructions of computed tomography (CT) scans.

MATERIALS AND METHODS

Ten rectangular acrylic blocks were prepared with titanium molybdenum alloy (TMA) markers spaced from 1 to 10 mm, respectively. A plastic sphere was prepared with 10 sets of TMA markers spaced at variable intervals of 1 to 10 mm. Each object was scanned three times at 3-mm slice thicknesses and 1.5 mm with 0.5 mm overlap slice thicknesses, as well as positioned in the CT scanner in two different directions (perpendicular and parallel) to the scanning beam. Intermarker distances of the reconstructed objects were then measured using the measurement tool of the MediCAD software and compared with measurements taken by hand with a vernier caliper.

RESULTS

Using the 3-mm cut protocol, the data indicated that inconsistency exists between intermarker distance in the scans when the rectangular objects were scanned parallel to the scanning beam. This finding was not seen using the 1.5-mm with 0.5-mm overlap slice thickness protocol. The intermarker distances for objects scanned perpendicular to the scanning beam were consistent but subject to demagnification in the range of 17% to 20% for both scanning protocols.

CONCLUSION

The orientation of the object to the scanning beam and slice thickness protocol appear to have an impact on the accuracy and variability of linear measurements taken in the x, y, z axes.

Multiplanar display of spiral CT data of the pulmonary hila in patients with lung cancer. Preliminary observations

Spiral or helical computed tomography (CT)-generated multiplanar reconstructions were used in the radiological assessment of the pulmonary hila in patients with central lung cancer. Twelve patients with non-small-cell lung cancer and hilar abnormalities were examined with contrast-enhanced spiral CT. Studies were performed on a Siemens Somatom S or Plus-S scanner using either a 24- or 32-second spiral. The study volume was from the arch of the aorta to the inferior pulmonary veins done in a single breath-hold, using 4-mm collimation, and reconstructed at 2-mm intervals. We assessed the quality of vascular enhancement and of multiplanar reconstructions. Bronchoscopic, surgical, and pathological findings were correlated. Excellent vascular opacification and good-quality reconstructions were obtained in all patients. No interscan motion was detected. No problems were encountered with the breathholding technique or in the reconstruction of images, even in patients with poor respiratory function. Multiplanar reconstructions were useful for the evaluation of mediastinal including vascular and airways invasion, for optimal definition of lymph node groups, for the planning of bronchoscopically guided biopsy, as well as for endobronchoscopic laser coagulation therapy and surgical treatment. Spiral CT-generated multiplanar reconstructions of the hila are helpful for staging, solving problems, guiding bronchoscopy, and planning surgery. Even patients with limited respiratory reserve can successfully complete the examination.