Variation Of Anatomical Structures Research Articles

TH-E-L100F-01: Advances in Simulation Tools and Their Applications to CT, PET/CT and SPECT/CT

In CT, PET/CT and SPECT/CT imaging research, we are often involved in the design, development and evaluation of instrumentation, data acquisition methods, and image reconstruction and processing techniques. Ideally, clinical trials using patient images from actual imaging systems should be used in the evaluation studies. In practice, clinical trials are difficult to perform due to the difficulties and the high costs in acquiring ‘good quality’ clinical images and physicians' time to read them. Most importantly, there is a lack of known ‘truth’ in most clinical images. In the past, although computer simulation methods allowed generation of a large number of images with known ‘truth’, they suffered from the availability of computer generated phantoms that realistically model human anatomy and physiological functions and the ability to generate simulate data that accurately represent data acquired from actual medical imaging systems. We have developed a 4D computer generated phantom that are based on the Visible Human data and cardiac and respiratory gated MRI and CT data from normal human subjects. The non-uniform rational b-splines (NURB) computer graphics tools were used to allow accurate modeling of the shapes of 3D anatomical structures and generation of collections of phantoms that represent variations in anatomical structures and physiological functions found in different patient populations. Also, analytical and Monte Carlo simulation methods have been developed to provide data that accurately model the imaging system geometry, and photon interactions in the phantom and within the imaging system. Applications of the simulation tools to CT, PET/CT and SPECT/CT imaging research will be demonstrated with sample research projects. They demonstrate the potential utility of the simulation tools in a wide variety of applications in the research and development of instrumentation, image reconstruction and processing methods of different medical imaging modalities in the years to come.

MO‐E‐330A‐05: Evaluation of Similarity Measures for Use in Intensity‐Based Registration in Radiotherapy

Purpose: In radiotherapy, the implementation of automated patient positioning depends on optimal selection of a similarity measure. Visual inspection of a registration is insufficient for evaluating performance of a measure, since high precision registration is usually involved. A general methodology is presented for evaluation of a measure based on convergence, precision and systematic errors for 2D and 3D imaging. Method and Materials: The following common metrics were studied: mean pixelwise product (PROD), normalized correlation coefficient (NCC), partitioned intensity uniformity (PIU), mutual information (MI), normalized mutual information (NMI), entropy of the difference image (ED), gradient correlation (GC), gradient difference (GD), and pattern intensity (PI). Imaging from an anthropomorphic phantom and clinical data were used. Portal images were acquired with a video camera EPID and a flat‐panel imager. Kilovoltage digitally reconstructed radiographs (DRR) and megavoltage DRRs (MVDRR) were used for reference images. The following shifts were carried out: translations from −10 mm to +10 mm with 0.2 mm increments, and/or rotations from −10° to +10° with 0.2° increments. The effect down‐sampling and image type were also investigated. Results: The selection of a measure depended on image type and down‐sampling schedule. PROD introduced the largest systematic error. NCC, PIU, MI, NMI, and GD typically had systematic errors less than 1 mm and 1°. Down‐sampling has less effect on NCC, PIU, and GC. MI, NMI, GC, GD, and PI have sharp “peaks” around their global optima. Asymmetry in the objective function was observed in NCC, PIU, MI, NMI, and ED. Registrations using GC, GD, and PI were less sensitive to the variation of anatomical structures. Using MVDRRs instead of DRRs increased objective function smoothness. Conclusion: A general methodology was presented for evaluation and selection of a measure. Selection was application dependent, indicating necessity of a validation study, as presented here, prior to clinical use.

Neuroimaging and Psychopharmacology.

This review presents the most recent research concerning neuroimaging in developmental disabilities. Changes in structure and activation have been found in children with ADHD and learning disabilities, following intervention. For the children with learning disabilities changes in activation have been found following intensive behavioral and academic intervention. Structural and activation differences in the auditory processing regions of the brain were found prior to academic intervention, with activation differences found for those children responding to the reading programs. Children with ADHD have been found to show differences in brain structures with few studies evaluating the differences in activation following medication. Emerging evidence indicates differences in the frontal regions of the brain for children who respond successfully to medication. Finally, a discussion of the variables that can impact the results in neuroimaging studies is presented. Further study is needed in this area, and additional variables of concern are also discussed. With the advent of structural and functional neuroimaging, it is now possible to obtain information about brain activity during selected tasks as well as differences in brain structure across various psychological disorders. Contemporary neurological models for language, reading, and attention suggest that these complex behaviors are a result of the interaction of functional systems that are separate (Luria, 1980). During development, these systems change in organization and possibly in structure in response to neurological maturation, experience, and environmental influences (Semrud-Clikeman, 1997). Variations in anatomical structure can contribute to differing types of developmental disabilities depending on the type and severity of deviance. To be useful, these models need to

A brainstem stereotactic atlas in a three-dimensional magnetic resonance imaging navigation system: first experiences with atlas-to-patient registration.

The authors describe a computer-resident digital representation of a stereotactic atlas of the human brainstem, its semiautomated registration to sagittal fast low-angle shot three-dimensional (3-D) magnetic resonance (MR) imaging data sets in 27 healthy volunteers and 24 neurosurgical patients, and an analysis of the subsequent transforms needed to refine the initial registration. Contour drawings from the atlas, which offer the 70th percentile of variation of anatomical structures, were interpolated into an isotropic 3-D representation. Initial atlas-to-patient registration was based on the fastigium/ventricular floor plane reference system. The quality of the fit was evaluated using superimposition of the atlas and MR images. If necessary, the atlas was tailored to the individual anatomy by using additional transforms. On average, the atlas had to be stretched by 2 to 6% in the three directions of space. Scale factors varied over a broad range from -8 to +19% and the benefit of visual interactive control of the atlas-to-patient registration was evident. Analysis of distances within the pons measured in the midsagittal MR imaging slices and the required scale factors revealed significant correlations that may be used to reduce the amount of user interaction in the coregistration substantially. In 70.6% of the cases, the atlas had to be shifted in a cranial direction along the brainstem axis (in 25.5% of cases 3-4 mm, in 45.1% of cases 1-2 mm). This was due to a more caudal position of the fastigium cerebelli on the MR images compared with the atlas. This observation, in conjunction with the variability of the height of the fourth ventricle in our MR imaging data (range 6.1-15.2 mm, mean 10.1 mm, standard deviation 1.8 mm) calls into question the role of the fastigium cerebelli as an anatomical landmark for localization within the brainstem.

Topographic variations in anatomical structures of the anterior neck of childrenAn ultrasonographic study

Objective. Tracheostomies in children are frequently used for temporary airway support during surgical procedures. In pediatric patients with congenital craniofacial malformations, preoperative assessment of the delicate anatomy of the airway is necessary. The purpose of this study was to assess the ultrasonographic anatomy of the anterior neck with regard to the performance of tracheostomy. Study design. Ultrasonographic investigation was done in 50 pediatric patients (age range, 6 to 15 years) to analyze the relationships among the anatomical structures that are of practical interest with respect to tracheostomy. Results. The data reveal that information concerning variations in anatomical structures lying in the immediate vicinity of the tracheostomy site was readily obtainable with the techniques used. Conclusions. In pediatric patients requiring tracheostomy for surgical treatment of severe congenital craniofacial malformations, preoperative ultrasonography may be used to diagnose individual anatomical variations at the tracheostomy site. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:429-36)

Anatomical variations in human carotid bodies.

The variations in anatomical structure and position of both carotid bodies were noted in 100 consecutive subjects who came to necropsy. Considerable variations in form were found. Although most carotid bodies (83% on the right and 86% on the left) were of the classic ovoid type, an appreciable minority was bilobed (9% on the right and 7% on the left) or double (7% on the right and 6% on the left); 1% were leaf shaped. All these anatomical variants have to be distinguished from the pathologically enlarged carotid body that may have a smooth or finely nodular surface. Anatomical variants (such as the bilobed) may themselves enlarge as a consequence of carotid body hyperplasia.

Vesico-umbilical fistula: A complication of umbilical artery cutdown

A vesico-umbilical fistula occurred following cut down for catheterization of the umbilical artery in a premature infant; a previously unreported complication. Knowledge of the variations in anatomical structure of the urachus and umbilical arteries at birth will help to prevent this complication.

The interpretation of mean transit time measurements for multiphase tissue systems

A model-independent proof of the central-volume principle for multiphase tissue systems is presented. This derivation emphasizes the transport processes which occur within the system, and the physical constraints which the system must satisfy for valid application of the principle. These constraints include: (i) the fluid flowing into the system must be equivalentlylabelled; (ii) the system under study must be part of a larger system which has no diffusive inlets or outlets. The derivation shows that the definition of the volume of distribution and the choice of appropriate partition coefficients for evaluation of this quantity, are independent of any assumption concerning tracer equilibrium between phases as a whole. A less restrictive definition of equivalent labelling also results from the proof. The relationship between the mean transit times measured by global residue detection and by “snapshot” outflow detection is derived. If diffusion of tracer across the boundaries of the monitored system is significant compared to convective transport, then these two transit times will not have identical values. The conditions under which valid measurements of regional, i.e. local, physiological variables can be performed by residue detection are also discussed, and it is shown that regional residue-detection measurements may be used to assess variations in anatomical structure throughout a larger region. However, the use of the height/area method for calculating regional perfusion can lead to error when tracer enters the detector field by diffusion, as opposed to convection, or when a significant amount of diffusion occurs before tracer enters the observed region.