Identification of a stable reference area for superimposing mandibular digital models.

PURPOSE: The purpose of this retrospective study was to assess the stability of buccal and lingual alveolar bone surfaces for superimposing three-dimensional (3D) digital models of dental casts. MATERIALS AND METHODS: The pre- and posttreatment dental casts and lateral cephalometric radiographs were obtained from 10 adult patients who had undergone orthodontic treatment entailing the extraction of four premolars. Five of them had bilateral mandibular tori and the other 5 patients had no torus. Dental casts were scanned with a three-dimensional (3D) surface scanning system and 3D digital models were reconstructed using 3D reverse modeling software. The pre- and posttreatment digital models were superimposed on the following reference areas by the best-fit method: Area 1, bilateral lingual surfaces of the alveolar process of the posterior teeth; Area 2, the lingual alveolar surface of the anterior and posterior teeth; Area 3, bilateral surfaces of the posterior teeth's buccal and lingual alveolar surfaces; Area 4, bilateral mandibular tori. The horizontal and vertical movements of the mandibular central incisors and first molars were measured on cephalometric radiographs and on the 3D digital models. RESULTS: In the 5 patients without a mandibular torus, the median differences between cephalograms and 3D digital models ranged from 0.8-1.9 mm and the maximum differences from 1.5-10.0 mm. The median and maximum differences between cephalograms and 3D digital models superimposed on Area 2 were greater than those superimposed on Areas 1 and 3. In the patients with mandibular tori, the median differences between cephalograms and 3D digital models were under 1.0 mm, the maximum difference being 0.7 mm. CONCLUSION: The buccal and lingual alveolar surface near the dentition seems to be inappropriate as a reference area for superimposing 3D mandibular digital models of patients without a mandibular torus. Mandibular tori in adult patients are stable structures which can be used as reference areas for the superimposition of 3D mandibular digital models.

Importance of Reference Muscle Selection in Quantitative Signal Intensity Analysis of T2-Weighted Images of Myocardial Edema Using a T2 Ratio Method.

OBJECTIVES: The purpose of our study was to identify the suitability of various skeletal muscles as reference regions for calculating the T2 SI ratio for a semiautomated quantification of the extent of myocardial edema with T2-weighted images. METHODS: Thirty-four patients with acute myocardial infarction (MI) were enrolled. The extent of myocardial edema was determined by T2 SI ratio map, using 4 different muscles as reference: major and minor pectoralis, serratus anterior, teres minor-infraspinatus, and subscapularis. The size of myocardial edema as visually quantified was used as the standard of truth. The control group consisted of 15 patients with chronic MI. Intra- and interobserver variability were assessed. RESULTS: Due to poor image quality four patients were excluded from the analysis. In acute MI patients, serratus anterior muscle showed the strongest correlation with the visual analysis (r = 0.799; P < 0.001) and low inter- and intraobserver variability, while the other muscles resulted in a significant interobserver variability. In contrast, the use of other muscles as a reference led to overestimating edema size. CONCLUSIONS: In acute MI patients, serratus anterior resulted to be the most reliable and reproducible muscle for measuring the extent of myocardial edema.

Developing a stereotypical Drosophila brain atlas.

Brain research requires a standardized brain atlas to describe both the variance and invariance in brain anatomy and neuron connectivity. In this study, we propose a system to construct a standardized 3D Drosophila brain atlas by integrating labeled images from different preparations. The 3D fly brain atlas consists of standardized anatomical global and local reference models, e.g., the inner and external brain surfaces and the mushroom body. The averaged global and local reference models are generated by the model averaging procedure, and then the standard Drosophila brain atlas can be compiled by transferring the averaged neuropil models into the averaged brain surface models. The main contribution and novelty of our study is to determine the average 3D brain shape based on the isosurface suggested by the zero-crossings of a 3D accumulative signed distance map. Consequently, in contrast with previous approaches that also aim to construct a stereotypical brain model based on the probability map and a user-specified probability threshold, our method is more robust and thus capable to yield more objective and accurate results. Moreover, the obtained 3D average shape is useful for defining brain coordinate systems and will be able to provide boundary conditions for volume registration methods in the future. This method is distinguishable from those focusing on 2D + Z image volumes because its pipeline is designed to process 3D mesh surface models of Drosophila brains.

Generating a minimal set of templates for the hippocampal region in MR neuroimages.

OBJECTIVES: We detail a procedure for generating a set of templates for the hippocampal region in magnetic resonance (MR) images, representative of the clinical conditions of the population under investigation. METHODS: The first step is robust standardization of the intensity scale of brain MR images, belonging to patients with different degrees of neuropathology (Alzheimer's disease). So similar tissues have similar intensities, even across images coming from different sources. After the automatic extraction of the hippocampal region from a large dataset of images, we address template generation, choosing by clusterization methods a small number of the extracted regions. RESULTS: We assess that template generation is largely independent on the clusterization method and on the number and the clinical condition of the patients. The templates are chosen as the most representative images in a population. The estimation of the "minimum" number of templates for the hippocampal region can be proposed, using a metric based on the geometrical position of the extracted regions. CONCLUSIONS: This study describes a simple and easily reproducible procedure to generate templates for the hippocampal region. It can be generalized and applied to other brain regions, which may be relevant for neuroimaging studies.

Digital evaluation of the reproducibility of implant scanbody fit--an in vitro study.

Dental restorations are increasingly manufactured by CAD/CAM systems. Currently, there are two alternatives for digitizing dental implants: direct intra-oral data capturing or indirect from a master cast, both with transfer caps (scanbodies). The aim of this study was the evaluation of the fit of the scanbodies and their ability of reposition. At the site of the first molars and canines, implants were placed bilaterally in a polymer lower arch model (original model), and an impression was taken for fabricating a stone cast (stone model). Ten white-light scans were obtained from the original and the stone model with the scanbodies in place. The scanbodies were retrieved after each scan and re-attached to the same implant or lab analogue. The first scan of the series served as control in both groups. The subsequent nine scans and control were superimposed using inspection software to identify the discrepancies of the four scanbodies in both experimental groups. The systematic error of digitizing the models was 13 µm for the polymer and 5 µm for the stone model. The mean discrepancy of the scanbodies was 39 µm (±58 µm) on the original implants versus 11 µm (±17 µm) on the lab analogues. The difference in scanbody discrepancy between original implants and lab analogues was statistically significant (p < 0.05, Mann-Whitney U test). Scanbody discrepancy was higher on original implants than on lab analogues. Fit and reproducibility of the scanbodies on original implants should be improved to achieve higher accuracy of implant-supported CAD/CAM fabricated restorations.

Evaluation of simulated external root resorptions with digital radiography and digital subtraction radiography.

INTRODUCTION: Root resorption can cause damage in orthodontic patients. Digital subtraction radiography (DSR) is a useful resource for the detection of mineral losses. The purpose of this study was to compare the efficacy of digital radiography (DR) and DSR in detecting simulated external root resorption. Examiner agreement between the 2 techniques was also evaluated. METHODS: Root resorptions of various sizes were simulated on the apical and lingual aspects of 49 teeth from 9 dry human mandibles. The teeth were radiographed in standardized conditions. The radiographs were registered with Regeemy Image Registration and Mosaicking (version 0.2.43-RCB, DPI-INPE, São José dos Campos, São Paulo, Brazil) and subtracted with Image Tool (University of Texas Health Science Center at San Antonio). The subtracted images and the digital radiographs were evaluated by 3 oral radiologists. RESULTS: No statistically significant differences were found for the methods in the detection of apical root resorptions, independently from lesion size, and of lingual resorptions of 1.2 mm or greater. DSR was significantly better than DR for detection of lingual resorptions up to 1 mm. Resorptions less than 0.5 mm were not precisely detected by either method. DSR provided better intraexaminer and interexaminer agreement than did DR. CONCLUSIONS: Both methods are precise for detection of apical root resorptions as small as 0.5 mm and lingual resorptions of 1 mm or more. However, DSR frequently performed better than did DR.

FDG PET and PET/CT: EANM procedure guidelines for tumour PET imaging: version 1.0.

The aim of this guideline is to provide a minimum standard for the acquisition and interpretation of PET and PET/CT scans with [18F]-fluorodeoxyglucose (FDG). This guideline will therefore address general information about[18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) and is provided to help the physician and physicist to assist to carrying out,interpret, and document quantitative FDG PET/CT examinations,but will concentrate on the optimisation of diagnostic quality and quantitative information.

Standardized platform for coregistration of nonconcurrent diffuse optical and magnetic resonance breast images obtained in different geometries.

We present a novel methodology for combining breast image data obtained at different times, in different geometries, and by different techniques. We combine data based on diffuse optical tomography (DOT) and magnetic resonance imaging (MRI). The software platform integrates advanced multimodal registration and segmentation algorithms, requires minimal user experience, and employs computationally efficient techniques. The resulting superposed 3-D tomographs facilitate tissue analyses based on structural and functional data derived from both modalities, and readily permit enhancement of DOT data reconstruction using MRI-derived a-priori structural information. We demonstrate the multimodal registration method using a simulated phantom, and we present initial patient studies that confirm that tumorous regions in a patient breast found by both imaging modalities exhibit significantly higher total hemoglobin concentration (THC) than surrounding normal tissues. The average THC in the tumorous regions is one to three standard deviations larger than the overall breast average THC for all patients.

NEMA NU 2-2001 performance measurements of an LYSO-based PET/CT system in 2D and 3D acquisition modes.

UNLABELLED: The National Electrical Manufacturers Association (NEMA) NU 2-2001 performance measurements were conducted on the Discovery RX, a whole-body PET/CT system under development by GE Healthcare. The PET scanner uses 4.2 x 6.3 x 30 mm lutetium yttrium orthosilicate (LYSO) crystals grouped in 9 x 6 blocks. There are 24 rings with 630 crystals per ring and the ring diameter is 88.6 cm. The transaxial and axial fields of view are 70.0 and 15.7 cm, respectively. The scanner has retractable septa and can operate in both 2-dimensional (2D) and 3-dimensional (3D) modes. 2D acquisitions use ring differences of +/-4 for direct and +/-5 for cross slices; 3D acquisitions use a ring difference of 23. The coincident window width is 6.5 ns and the energy window is 425-650 keV. Other than the detectors, the system uses the same hardware and software as a Discovery ST. The CT scanner is a 16-slice LightSpeed; the performance characteristics of the CT component are not included herein. METHODS: Performance measurements of sensitivity, spatial resolution, image quality, scatter fraction and counting rate performance, and image quality were obtained using NEMA methodology. RESULTS: The system sensitivity in 2D and 3D was measured as 1.7 cps/kBq and 7.3 cps/kBq, respectively. The transaxial resolution for 2D (3D) was 5.1 mm full width at half maximum (FWHM) (5.0 mm) at 1 cm from gantry center and the radial and tangential resolutions were 5.9 mm (5.9 mm) and 5.1 mm (5.2 mm) at 10 cm, respectively. The axial resolution for 2D (3D) was 4.8 mm FWHM (5.8 mm) and 6.3 mm (6.5 mm) at 1 cm and 10 cm from gantry center, respectively. The scatter fraction was 13.1% and 31.8% in 2D and 3D. The peak noise equivalent count rate (NECR) was 155 kcps at 92.1 kBq/mL in 2D and 117.7 kcps at 21.7 kBq/mL in 3D for a noise-free estimation of randoms. The contrast of the 22, 17, 13, and 10 mm hot spheres in the image quality phantom in 2D (3D) were 74.6% (72.4%), 56.7% (59.5%), 46.2% (44.6%), and 17.9% (18.0%), respectively. CONCLUSION: The Discovery RX is a scanner that possesses high NECR, low scatter fraction, and good spatial resolution characteristics.

The challenges in creating reference maps for verification of ultrasound images.

In the development of new medical imaging techniques, references to which the images can be compared are necessary if one wants to assess how precise the images are. This is especially interesting in diagnostic ultrasound where a number of artefacts influence the image. The reference can either be derived from a phantom with precisely known properties and geometry, from the specifications of a computer phantom (simulated images) or from evaluation of biological tissue. The third approach can be conducted with other medical imaging modalities (CT, MRI, etc.) or "destructive testing" involving histology. In this paper, aspects of the latter method is considered in detail. Formalin fixed tissue is moulded into an agar block containing at set of fiducial markers. The block is scanned with ultrasound. Both tissue and fiducial markers are imaged. The block is afterwards sliced at the location of the fiducial markers. The slices are then photographed and analyzed histologically. From this data, reference maps with similar geometry as the ultrasound images can be created. Ideally, for each pixel in the ultrasound image, these reference maps indicate tissue type, such as collagen poor tissue, collagen rich tissue, etc. Many of the sources of error as well as the challenges with such a method are discussed.

Standardized evaluation methodology for 2-D-3-D registration.

In the past few years, a number of two-dimensional (2-D) to three-dimensional (3-D) (2-D-3-D) registration algorithms have been introduced. However, these methods have been developed and evaluated for specific applications, and have not been directly compared. Understanding and evaluating their performance is therefore an open and important issue. To address this challenge we introduce a standardized evaluation methodology, which can be used for all types of 2-D-3-D registration methods and for different applications and anatomies. Our evaluation methodology uses the calibrated geometry of a 3-D rotational X-ray (3DRX) imaging system (Philips Medical Systems, Best, The Netherlands) in combination with image-based 3-D-3-D registration for attaining a highly accurate gold standard for 2-D X-ray to 3-D MR/CT/3DRX registration. Furthermore, we propose standardized starting positions and failure criteria to allow future researchers to directly compare their methods. As an illustration, the proposed methodology has been used to evaluate the performance of two 2-D-3-D registration techniques, viz. a gradient-based and an intensity-based method, for images of the spine. The data and gold standard transformations are available on the internet (http://www.isi.uu.nl/Research/Databases/).

Performance characteristics of a newly developed PET/CT scanner using NEMA standards in 2D and 3D modes.

UNLABELLED: This study evaluates the 2-dimensional (2D) and 3-dimensional (3D) performance characteristics of a newly developed PET/CT scanner using the National Electrical Manufacturers Association (NEMA) NU 2-1994 (NU94) and NEMA NU 2-2001 (NU01) standards. The PET detector array consists of 10,080 individual bismuth germanate crystals arranged in 24 rings of 420 crystals each. The size of each crystal is 6.3 x 6.3 x 30 mm in the axial, transaxial, and radial dimensions, respectively. The PET detector ring diameter is 88.6 cm with axial and transaxial fields of view (FOVs) of 15.7 and 70 cm, respectively. The scanner has a uniform patient port of 70 cm throughout the PET and CT FOV, and the PET scanner is equipped with retractable septa to allow 2D and 3D imaging. METHODS: Spatial resolution, scatter fraction, sensitivity, counting rate, image quality, and accuracy as defined by the NEMA protocols of NU94 and NU01 for 2D and 3D modes are evaluated. The 2D mode data were acquired with a maximum ring difference of 5, whereas the 3D mode acquisition used ring differences of 23. Both 2D and 3D mode data were acquired with an energy window of 375-650 keV. Random estimation from singles counting rate was applied to all relevant analysis. In addition, images from 2 clinical whole-body oncology studies acquired in 2D and 3D modes are shown to demonstrate the image quality obtained from this scanner. RESULTS: The 2D NU94 transaxial resolution is 6.1-mm full width at half maximum (FWHM) 1 cm off center and increases to 6.9 mm tangential and 8.1 mm radial at a radius (R) of 20 cm. NU01 2D average transaxial (axial) FWHM resolution measured 6.1 (5.2) mm at R = 1 cm and 6.7 (6.1) mm at R = 10 cm. The NU94 scatter fraction for 2D (3D) was 13% (29%), whereas the NU01 scatter fraction gave 19% (45%). NU01 peak 2D (3D) noise equivalent counting rate (T(2)/[T + R + S]) was 90.2 (67.8) kilocount per second (kcps) at 52.5 (12) kBq/mL. Total 2D (3D) system sensitivity for true events is 8 (32.9) kcps/kBq/mL for NU94 and 1.95 (9.2) kcps/Bq for NU01. CONCLUSION: The results show excellent system sensitivity with relatively uniform resolution throughout the FOV, making this scanner highly suitable for whole-body studies.

Acquisition protocol considerations for combined PET/CT imaging.

UNLABELLED: Since its introduction in 1998, dual-modality PET/CT imaging has received great attention in the medical community. For the first time, patients can be examined with both CT and PET in a single examination. A whole-body survey is the standard mode of acquisition. The CT images are used for anatomic reference of the tracer uptake patterns imaged in PET, as well as for attenuation correction of the PET data. The routine use of CT-based attenuation correction and user preferences for the quality and type of the CT examination have led to the introduction of different PET/CT scanning protocols. DISCUSSION: Two general approaches to PET/CT imaging can be distinguished today. One uses CT as a fast transmission source with little additional information for anatomic labeling. The other uses CT as a fast transmission source as well as a state-of-the-art diagnostic tool to maximize image quality using optimal acquisition parameters together with oral and intravenous contrast agents. Variations of these approaches share common concerns about image artifacts that result from mismatches in respiration and patient positioning between the CT and the PET examinations. Protocol requirements for the more complex radiologic PET/CT scenario also include alternative contrast application schemes or modifications to the attenuation correction procedure to handle CT contrast agents appropriately. CONCLUSION: High-quality PET/CT studies can be provided routinely with existing PET/CT technology that is used efficiently by trained and motivated technologists and physicians. Only then will the potential diagnostic benefit of this new imaging modality be explored fully.

Optimisation of brain SPET and portability of normal databases.

Use of a normal database in quantitative regional analysis of brain single-photon emission tomography (SPET) facilitates the detection of functional defects in individual or group studies by accounting for inter-subject variability. Different reconstruction methods and suboptimal attenuation and scatter correction methods can introduce additional variance that will adversely affect such analysis. Similarly, processing differences across different instruments and/or institutions may invalidate the use of external normal databases. The object of this study was to minimise additional variance by comparing reconstructions of a physical phantom with its numerical template so as to optimise processing parameters. Age- and gender-matched normal scans acquired on two different systems were compared using SPM99 after processing with both standard and optimised parameters. For three SPET systems we have optimised parameters for attenuation correction, lower window scatter subtraction, reconstructed pixel size and fanbeam focal length for both filtered back-projection (FBP) and iterative (OSEM) reconstruction. Both attenuation and scatter correction improved accuracy for all systems. For single-iteration Chang attenuation correction the optimum attenuation coefficient (mu) was 0.45-0.85 of the narrow beam value (Nmu) before, and 0.75-0.85 Nmu after, scatter subtraction. For accurately modelled OSEM attenuation correction, optimum mu was 0.6-0.9 Nmu before and 0.9-1.1 Nmu after scatter subtraction. FBP appeared to change in-plane voxel dimensions by about 2% and this was confirmed by line phantom measurements. Improvement in accuracy with scatter subtraction was most marked for the highest spatial resolution system. Optimised processing reduced but did not remove highly significant regional differences between normal databases acquired on two different SPET systems.

The performance of projective standardization for digital subtraction radiography.

OBJECTIVE: We sought to test the performance and robustness of projective standardization in preserving invariant properties of subtraction images in the presence of irreversible projection errors. Study design Twenty bone chips (1-10 mg each) were placed on dentate dry mandibles. Follow-up images were obtained without the bone chips, and irreversible projection errors of up to 6 degrees were introduced. Digitized image intensities were normalized, and follow-up images were geometrically reconstructed by 2 operators using anatomical and fiduciary landmarks. Subtraction images were analyzed by 3 observers. RESULTS: Regression analysis revealed a linear relationship between radiographic estimates of mineral loss and actual mineral loss (R(2) = 0.99; P <.05). The effect of projection error was not significant (general linear model [GLM]: P >.05). There was no difference between the radiographic estimates from images standardized with anatomical landmarks and those standardized with fiduciary landmarks (Wilcoxon signed rank test: P >.05). Operator variability was low for image analysis alone (R(2) = 0.99; P <.05), as well as for the entire procedure (R(2) = 0.98; P <.05). The predicted detection limit was smaller than 1 mg. CONCLUSIONS: Subtraction images registered by projective standardization yield estimates of osseous change that are invariant to irreversible projection errors of up to 6 degrees. Within these limits, operator precision is high and anatomical landmarks can be used to establish correspondence.

Aortic blood flow subtraction: an alternative method for measuring total renal blood flow in conscious dogs.

We have measured total renal blood flow (TRBF) as the difference between signals from ultrasound flow probes implanted around the aorta above and below the renal arteries. The repeatability of the method was investigated by repeated, continuous infusions of angiotensin II and endothelin-1 seven times over 8 wk in the same dog. Angiotensin II decreased TRBF (350 +/- 16 to 299 +/- 15 ml/min), an effect completely blocked by candesartan (TRBF 377 +/- 17 ml/min). Subsequent endothelin-1 infusion reduced TRBF to 268 +/- 20 ml/min. Bilateral carotid occlusion (8 sessions in 3 dogs) increased arterial blood pressure by 49% and decreased TRBF by 12%, providing an increase in renal vascular resistance of 69%. Dynamic analysis showed autoregulation of renal blood flow in the frequency range <0.06-0.07 Hz, with a peak in the transfer function at 0.03 Hz. It is concluded that continuous measurement of TRBF by aortic blood flow subtraction is a practical and reliable method that allows direct comparison of excretory function and renal blood flow from two kidneys. The method also allows direct comparison between TRBF and flow in the caudal aorta.

Value of subtraction technique in Gd-DTPA-enhanced magnetic resonance angiography of the thoracic aorta.

AIM: To assess routine image subtraction in 3D gadopentate dimeglumine (Gd-DTPA)-enhanced magnetic resonance (MR) angiography of the thoracic aorta. MATERIALS AND METHODS: This was a prospective study of 22 consecutive patients referred for magnetic resonance imaging (MRI) of the thoracic aorta. All patients had 3D MR aortography (TR/TE/FA; 5/2 ms/25 degrees ) performed before and after bolus intravenous injection of Gd-DTPA. The Gd-DTPA enhanced and unenhanced data sets were subtracted and maximum intensity projections (MIP) projections of the thoracic aorta were performed. The standard unsubtracted MIP images were initially evaluated. These were then reviewed together with the subtracted images to assess for additional diagnostic information. Signal to noise ratios (SNR) and contrast to noise ratios (CNR) were measured. RESULTS: In four cases there was mild image degradation due to patient movement. In no case did subtraction alter the diagnosis. The mean SNR in the unsubtracted MIP images was 10.8 +/- 4.0 (median 11.1) and on the subtracted images was 21.2 +/- 9.9 (median 20.7;P < 0.0001). The mean aorta-to-mediastinal fat CNR was 3.9 +/- 2.8 (median 3.9) on the unsubtracted images and 15.0 +/- 10.6 (median 13) on the subtracted images (P < 0.0001). The mean aorta-to-vertebral body CNR was 5.2 +/- 3.1 (median 4.4) on the unsubtracted images and 15.1 +/- 9.3 on the subtracted images (P < 0.0001). CONCLUSION: Image subtraction significantly improved both the SNR and CNR, but did not alter the final diagnosis, and does not appear warranted in routine practice.