Volume rendering quantification algorithm for reconstruction of CT volume-rendered structures: Part I. Cerebral arteriovenous malformations

Knowledge-driven 3-D extraction of the masseter from MR data

In this paper, we propose a knowledge-driven highly automatic methodology for extracting the masseter from magnetic resonance (MR) data sets for clinical purposes. The masseter is a muscle of mastication which acts to raise the jaw and clench the teeth. In our initial work, we designed a process which allowed us to perform 2-D segmentation of the masseter on 2-D MR images. In the methodology proposed here, we make use of ground truth to first determine the index of the MR slice in which we will carry out 2-D segmentation of the masseter. Having obtained the 2-D segmentation, we will make use of it to determine the region of interest (ROI) of the masseter in the other MR slices belonging to the same data set. The upper and lower thresholds applied to these MR slices, for extraction of the masseter, are determined through the histogram of the 2-D segmented masseter. Visualization of the 3-D masseter is achieved via volume rendering. Our methodology has been applied to five MR data sets. Validation was done by comparing the segmentation results obtained by using our proposed methodology against manual contour tracings, obtaining an average accuracy of 83.5%

Opacity transfer function optimization for volume-rendered computed tomography images of the prostate

RATIONALE AND OBJECTIVES

The selection of an opacity transfer function is essential for volume visualization. Computed tomography (CT) scans of the pelvis were used to determine an optimal opacity transfer function for use in radiotherapy.

MATERIALS AND METHODS

On sample datasets (a mathematical phantom and a patient pelvis CT scan), standard viewing orientations were selected to render the prostate. Opacity functions were selected via (1) trapezoidal manual selection, (2) trapezoidal semiautomatic selection, and (3) histogram volume-based selection. Using an established metric, the errors using each of these methods were computed.

RESULTS

Trapezoidal manual opacity function optimization resulted in visually acceptable images, but the errors were considerable (6.3-9.1 voxel units). These errors could be reduced with the use of trapezoidal semiautomatic selection (4.9-6.2 voxel units) or with histogram volume-based selection (4.8-7.9 voxel units). As each visualization algorithm focused on enhancing the boundary of the prostate using a different approach, the scene information was considerably different using the three techniques.

CONCLUSION

Improved volume visualization of soft tissue interfaces was achieved using automated optimal opacity function determination, compared with manual selection.

Craniofacial measurements based on 3D-CT volume rendering: implications for clinical applications

OBJECTIVES

This study was designed to determine the precision and accuracy of anthropometric measurements using three-dimensional computed tomography (3D-CT) volume rendering by computer systems for craniofacial clinical applications, and to compare the craniometric landmarks using bone and soft tissue protocols.

METHODS

The study population consisted of 13 cadaver heads that were examined with spiral CT. The archived CT data were transferred to a workstation, and 3D-CT volume rendered images were generated using computer graphics tools. Linear measurements (n = 10), based upon conventional craniometric anatomical landmarks (n = 08), were identified in 2D-CT and in 3D-CT images by two radiologists twice each independently, and then performed by 3D-CT imaging using a computer graphics systems using bone and soft tissue protocols. In total, 520 imaging measurements were made. The soft tissues were subsequently removed from the cadaver heads and the measurements were repeated using an electromagnetic 3 Space trade mark digitizer.

RESULTS

The results demonstrated no statistically significant difference between interobserver and intraobserver measurements or between imaging and physical measurements in both 3D-CT protocols. The standard error was found to be between 0.45% and 1.44% for all the measurements in both protocols, indicating a high level of precision. Furthermore, there was no statistically significant difference between imaging and physical measurements (P > 0.01). The error between the mean actual and mean 3D-based linear measurements was 0.83% for bone and 1.78% for soft tissue measurements, demonstrating high accuracy of both 3D-CT protocols.

CONCLUSIONS

3D-CT volume rendering images using craniometric measurements can be used for anthropological studies involving craniofacial applications.

Intensity-Modulated Radiation Therapy for Prostate Cancer

Prostate cancer is among the most common solid malignancies. A number of treatment alternatives exist for localized prostate cancer, including observation, prostatectomy, brachytherapy, and external-beam radiation therapy (EBRT). External-beam radiation therapy has changed dramatically during the past several years. Older techniques paved the way for 3-dimensional conformal radiation therapy (CRT), which in turn facilitated the introduction of intensity-modulated radiation therapy (IMRT). The prostate has served as a model disease site for the implementation of IMRT. As indicated by a growing body of experience, IMRT for prostate cancer represents a major technologic and clinical advance for radiation therapy. In this article, a review is provided of the evolution of EBRT leading to IMRT, the unique features making the prostate an ideal disease site for employing IMRT, the details of the clinical implementation of prostate IMRT and supporting technologic advancements, and the currently reported clinical outcomes of IMRT in prostate cancer. In addition, future directions of prostate IMRT, both technologic and clinical, are discussed.

3D volume rendering using multislice CT for dental implants

OBJECTIVES

To determine the precision and accuracy of three-dimensional (3D) volume rendering spiral multislice computed tomography (CT)-based linear measurements of the mental foramen for dental implants, in vitro, and their precision, in vivo.

METHODS

Five cadaver heads were imaged by multislice spiral CT (Toshiba Aquilion) with 0.5 mm thick axial slices (0.5 mm/0.5 s of table feed) at 0.5 mm interval reconstructions. The image data sets were transferred to a networked computer workstation. Using computer graphics the data were analysed with a 3D volume rendering technique using Vitrea software. Two oral and maxillofacial radiologists, independently, made electronic linear measurements from the superior border of the mental foramen to the crest of the alveolar process. The soft tissues were removed and physical measurements made using a 3 Space (Polhemus, Colchester, VT, USA) electromagnetic digitizer with a personal computer running Windows 98. The same linear measurements of 15 patients using the same imaging methodology were performed and the precision was analysed.

RESULTS

The findings showed no statistically significant inter- or intra-observer differences in vitro and in vivo, or between imaging and physical measurements in vitro (P>0.05).

CONCLUSIONS

3D multislice spiral CT imaging allows highly accurate measurements for dental implant placement in proximity to the mental foramen. Computer graphics software, using volume rendering is suitable for implant planning.

Compartments in arteriovenous malformation nidi demonstrated with rotational three-dimensional digital subtraction angiography by using selective microcatheterization. Report of three cases

Although in several histological studies of arteriovenous malformation (AVM) nidi the presence of compartments has been documented, no clinical study has been published. The present study was conducted to determine the presence of nidus compartments in clinical cases by using a new radiographic method. Two patients with unruptured and one with a ruptured AVM (all Spetzler-Martin Grade III) were studied. A microcatheter was superselectively introduced into each of two or three feeding arteries of the AVMs under three-dimensional (3D) angiographic guidance to obtain 3D images of the nidus by using rotational digital subtraction angiography. On 3D images the different feeding arteries were found to be independent from one another, which allowed the authors to confirm the presence of compartments. On the other hand, separate feeding arteries often had a common draining vessel. Compartments in AVM nidi were demonstrated by a novel rotational 3D angiographic procedure by using superselective microcatheterization, which should be useful for designing treatment strategies for large and complex AVMs.

Three-dimensional Contrastless Varicography by Spiral Computed Tomography

OBJECTIVE

to report and discuss preliminary results obtained in varicose limbs by means of a volume rendering (VR)-computed tomography (CT) technique without contrast medium injection.

MATERIALS AND METHODS

VR-CT and duplex sonography (US) were performed to visualise the superficial veins of the lower extremity in eight healthy and 12 varicose limbs.

RESULTS

VR-CT clearly demonstrated the 3D arrangement of the superficial veins and visualised small sized veins which were not visible at US examination.

CONCLUSIONS

VR-CT is not suitable for routine evaluation of varicose limbs. VR-CT 3D reconstructions may be useful in the evaluation of atypical varicosis. Further studies are needed to define the role of VR-CT in deep venous disease.