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PubMed1989

Effects of amiodarone on barium-induced automatic activity in guinea pig ventricular muscle.

1. The electrophysiological effects of a potent antiarrhythmic agent, amiodarone, on BaCl2-induced automaticity of guinea pig ventricular papillary muscle were studied by means of conventional microelectrode techniques. 2. BaCl2 (5 x 10(-4) M) depolarized the maximum diastolic potential of muscle preparation to about -62 mV and induced the spontaneous activity at rate of about 62 beats/min. 3. The application of amiodarone (4.4 x 10(-5) M to 1.1 x 10(-3) M) to the BaCl2-induced automatic muscle fibers decreased the spontaneous rate and slope of slow diastolic depolarization in a dose-dependent manner, associated with insignificant changes in action potential duration. 4. Amiodarone may exert the inhibitory effects of BaCl2-induced automaticity by decreasing steady-state conductance for the Na+ and Ca2+, probably thereby permitting the manifestation of antiarrhythmic properties in combination of its other actions.

Action Potentials↗
PubMed1988

Automatic methods for detection of tachyarrhythmias by antitachycardia devices.

Electrical devices play an increasingly important role in the control of tachyarrhythmias. Antitachycardia pacing and automatic defibrillation have been severely limited by the poor specificity of tachycardia discrimination in commercially available devices. Although absolute heart rate has been the principal means of automatic diagnosis, several new detection algorithms and methods are being investigated. Multiple electrode timing comparison, signal processing and pattern recognition are employed in these newer techniques. Although each offers some improvement over present technology, none is capable of identifying all arrhythmias. The methods employing comparison of atrial and ventricular rates, without additional criteria, are unable to detect ventricular tachycardia in the presence of 1:1 retrograde conduction. Electrographic analysis techniques require very stable electrodes and may not tolerate normal morphologic variations. A combination of two or more approaches may ultimately be required. All techniques will require that certain critical variables be programmable to allow for individualization in each clinical situation. Soft-ware-controllable devices and those capable of sensing from both the atria and the ventricles will provide the sophistication necessary for the implementation of complex tachycardia detection algorithms. This report reviews automatic tachycardia detection techniques in current use and under investigation.

Cardiac Pacing, Artificial↗
PubMed1988

Ectopic automatic atrial tachycardia in children: clinical characteristics, management and follow-up.

Ectopic automatic atrial tachycardia, an uncommon type of supraventricular tachycardia in children and adults, has been reported to be resistant to medical therapy, and surgical or cryoblation has been recommended. This report describes 10 infants and children (median age 6 months; range birth to 7.5 years) with automatic atrial tachycardia and their management and follow-up. Digoxin alone was unsuccessful in controlling tachycardia in all 10 patients but decreased the tachycardia rate by 5 to 20% in 8. Intravenous (0.1 mg/kg body weight per dose) and oral propranolol successfully suppressed tachycardia in three of five patients and oral propranolol successfully controlled tachycardia in two of five other patients. Class I antiarrhythmic agents--quinidine (three patients), procainamide (four patients) and phenytoin (three patients)--did not control tachycardia in any patients but made the tachycardia rate worse in three patients. Intravenous (5 mg/kg per dose) and oral amiodarone suppressed tachycardia in three of four patients and oral amiodarone suppressed it in another patient. Thus, intravenous propranolol and amiodarone were effective in acutely suppressing automatic ectopic atrial tachycardia and predicted the response to long-term oral therapy. One patient had persistent tachycardia after surgical ablation of the high right atrial ectopic focus, and another patient had unsuccessful catheter ablation of the high right atrial ectopic focus (25 J). During follow-up (10 to 28 months), ectopic atrial tachycardia resolved completely in four patients and was well controlled in four patients.

Administration, Oral↗
PubMed1996

Identification of severe and extensive coronary artery disease by automatic measurement of transient ischemic dilation of the left ventricle in dual-isotope myocardial perfusion SPECT.

OBJECTIVES: This study sought to assess whether a transient ischemic dilation ratio, determined from automatically derived stress and rest left ventricular volumes during stress technetium-99m (Tc-99m) sestamibi/rest thallium-201 dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT), is useful for the identification of patients with severe and extensive coronary artery disease. BACKGROUND: Transient ischemic dilation of the left ventricle on stress/redistribution thallium-201 scintigraphy has been shown to be a clinically useful marker of severe and extensive coronary artery disease. However, in practice, its assessment is highly subjective. This study automatically assessed the transient ischemic dilation ratio on the basis of a previously described algorithm to estimate three-dimensional ventricular boundaries. METHODS: Normal limits for the transient ischemic dilation ratio were developed using data from 54 patients with a low likelihood (< 5%) of coronary artery disease, and criteria for abnormality were developed based on data from 97 who under-went catheterization, of whom 34 had severe and extensive coronary artery disease, defined as > or = 90% stenosis in the proximal left anterior descending coronary artery or in two or more coronary arteries, and 63 had no coronary artery disease (15 patients) or mild to moderate coronary artery disease (48 patients). The criteria were then tested in a validation cohort of 77 additional patients who underwent catheterization, of whom 36 had severe and extensive coronary artery disease. The quantitative results of the dilation ratio were compared with the visual results of the dilation ratio and perfusion defect analysis. RESULTS: For normal limits, receiver operating characteristic curve analysis showed that abnormal transient ischemic dilation ratio values corresponded to left ventricular endocardial volume ratios > 1.22 (mean +/- 2 SD). Transient ischemic dilation assessment using these criteria for abnormality showed high sensitivity (24 [71%] of 34) and very high specificity (60 [95%] of 63) for severe and extensive coronary artery disease. When the analysis was applied to the prospective catheterization group, similar sensitivity and specificity for severe and extensive coronary artery disease were observed (77% and 92%, respectively). Significant agreement (p = 0.0001) was found between the degree of transient ischemic dilation and the Tc-99m sestamibi defect extent, the latter assessed by semiquantitative visual analysis (summed stress score). CONCLUSIONS: The automatic measurement of transient ischemic dilation in dual-isotope myocardial perfusion SPECT is a clinically useful marker that is sensitive and highly specific for detection of severe and extensive coronary artery disease.

Aged↗
PubMed1994

Screening of protein sequences databanks by Automat for search of host sequences integration and/or autoimmune disorders induction by retroviruses.

We have designed an efficient algorithm in order to detect systematically all the oligopeptides shared by a given protein with all the protein sequences in a databank. This software, Automat, also makes statistics on the number of shared oligopeptides. In the present study, we apply Automat on HIV-1 proteins to detect putative critical sites and to identify candidate viral antigens that may trigger autoimmune disorders. A list of pertinent similarities between HIV-1 proteins and human proteins, as detected by Automat, is reported.

Amino Acid Sequence↗
PubMedDate not supplied

IMPROMPTU: a system for automatic 3D medical image-analysis.

The utility of three-dimensional (3D) medical imaging is hampered by difficulties in extracting anatomical regions and making measurements in 3D images. Presently, a user is generally forced to use time-consuming, subjective, manual methods, such as slice tracing and region painting, to define regions of interest. Automatic image-analysis methods can ameliorate the difficulties of manual methods. This paper describes a graphical user interface (GUI) system for constructing automatic image-analysis processes for 3D medical-imaging applications. The system, referred to as IMPROMPTU, provides a user-friendly environment for prototyping, testing and executing complex image-analysis processes. IMPROMPTU can stand alone or it can interact with an existing graphics-based 3D medical image-analysis package (VIDA), giving a strong environment for 3D image-analysis, consisting of tools for visualization, manual interaction, and automatic processing. IMPROMPTU links to a large library of 1D, 2D, and 3D image-processing functions, referred to as VIPLIB, but a user can easily link in custom-made functions. 3D applications of the system are given for left-ventricular chamber, myocardial, and upper-airway extractions.

Computer Graphics↗
PubMed1996

Automatic leukocyte differentiation in bronchoalveolar lavage fluids of guinea pigs and brown-Norway rats.

Asthma is considered to be a chronic inflammatory response of the airways characterized by a leukocyte infiltration into the lungs. Whereas lymphocytes and macrophages are involved in the initiation and propagation of inflammation, both neutrophils and in particular eosinophils are considered to play major effector roles. Therefore, allergic animal models in various species have been established to assess leukocyte infiltration by bronchoalveolar lavage (BAL) of antigen-sensitized and antigen-challenged animals as an inflammatory parameter in asthma pharmacology. Differential leukocyte counts in BAL fluids are routinely assessed by visual microscopic analysis of stained slides after cytocentrifugation. This procedure is very time-consuming, and the underlying standard morphological criteria may vary between different observers. In the present paper, we propose an alternative automatic method for leukocyte differentiation in BAL fluids from ovalbumin-treated guinea pigs and Brown-Norway rats using Cobas Helios 5Diff from Hoffmann-La Roche. BAL samples are directly applied to the analyzer and are automatically mixed with "Eosinofix," which stabilizes leukocyte membranes and specifically stains eosinophils. By a combination of electric (resistance) and optical (light scatter) analysis, the lymphocytes, monocytes/macrophages, neutrophils, and eosinophils are discriminated and the total leukocyte numbers are obtained. For both animal species we found high correlations for all leukocyte populations by comparing the results obtained with Cobas Helios 5Diff and conventional microscopic analysis. The major advantage of the automatic method is the much lower (about one-third) time requirement.

Animals↗
PubMed1994

Automatic detection method of P300 waveform in the single sweep records by using a neural network.

Event-related potentials (ERPs) are responses related to the recognition of certain stimuli. P300 is the most important positive component in the ERP and appears around 300 ms after the target stimulus in the oddball paradigm. In our previous work, we proposed a method for the automatic detection of the P300 waveform in single-sweep records by using a correlation technique. However, determination of the threshold values of the P300 waveform for the correlation study was not an easy task. In skirting this problem, we developed an automatic method of detecting a single-sweep P300 waveform by using an artificial neural network. We selected appropriate characteristic parameters of positive peaks as input signals for the input layer units, and the weights between the layers were determined by using the back-propagation algorithm. The neural network for P300 detection was obtained automatically, based on the data of ERPs obtained from 11 healthy males, and gave substantial accuracy for P300 detection. Furthermore, by using this neural network we clarified the way in which the P300 waveform is judged visually by each inspector.

Acoustic Stimulation↗
PubMed2006

Automatic selection of the optimal cardiac phase for gated three-dimensional coronary x-ray angiography.

RATIONALE AND OBJECTIVES: For the reconstruction of the coronary arteries from rotational angiography data, a crucial point is the selection of the optimal cardiac phase for data reconstruction. To avoid time-consuming interactive selection of the optimal cardiac phase by visual inspection of multiple high-resolution data sets reconstructed at different cardiac phases, an automatic approach for deriving optimal reconstruction windows is attractive. MATERIALS AND METHODS: This paper presents a new approach to fully automatic selection of the optimal cardiac phase for image reconstruction. It is based on the analysis of a four-dimensional data set of the region of interest reconstructed at low-spatial resolution utilizing an image quality index, which quantifies the image quality of a single three-dimensional reconstructed volume. The derived image quality index utilizes the histogram information of a single temporal snapshot as a quality measure for the vessel reconstruction. The proposed technique was applied to 16 projection data sets obtained in eight pigs. RESULTS: Experiments to evaluate the proposed method based on user-defined image quality parameters serving as ground truth, showed a relatively high correlation (>84%) for high-quality (c(phi) > 0.95) images. CONCLUSION: An image-based technique is introduced, which is able to determine the optimal cardiac phase for 3D-RCA fully automatically. The proposed method was successfully applied to 16 data sets obtained in a total of 8 porcine models.

Algorithms↗
PubMed2004

Exposure to violent video games increases automatic aggressiveness.

The effects of exposure to violent video games on automatic associations with the self were investigated in a sample of 121 students. Playing the violent video game Doom led participants to associate themselves with aggressive traits and actions on the Implicit Association Test. In addition, self-reported prior exposure to violent video games predicted automatic aggressive self-concept, above and beyond self-reported aggression. Results suggest that playing violent video games can lead to the automatic learning of aggressive self-views.

Adolescent↗
PubMed2005

Neural mechanisms of automatic and direct processing of phobogenic stimuli in specific phobia.

BACKGROUND: The study aimed to identify brain activation during direct and automatic processing of phobogenic stimuli in specific phobia. METHODS: Responses to phobia-related and neutral pictures (spiders and mushrooms) were measured by means of event-related functional magnetic resonance imaging during two different tasks. In the identification task, subjects were asked to identify the object (spider or mushroom). In a demanding distraction task, subjects had to match geometric figures displayed in the foreground of the pictures. RESULTS: Phobics showed greater responses to spiders versus mushrooms in the left amygdala, left insula, left anterior cingulate gyrus (ACC), and left dorsomedial prefrontal cortex (DMPFC) during the identification task and in the left and right amygdala during the distraction task. All of these activations were also significantly increased compared to control subjects who did not show stronger brain activation to spiders versus mushrooms under any task condition. CONCLUSIONS: Our findings propose specific neural correlates of automatic versus direct evaluation of phobia-relevant threat. While the amygdala, especially the right amygdala, seems to be crucially involved in automatic stimuli processing, activation of areas such as the insula, ACC and DMPFC is rather associated with direct threat evaluation and requires sufficient attentional resources.

Adult↗
PubMed2004

Automatic bio-sampling chips integrated with micro-pumps and micro-valves for disease detection.

The present study reports a microfluidic system using the concept of membrane-movement to design and fabricate micro-pneumatic valves and pumps to form a bio-sensing diagnostic chip. The automatic bio-sampling system includes a micro-diagnostic chip fabricated by using MEMS (micro-electro-mechanical systems) technology and an automatic platform comprising of a control circuit, a compressed air source and several electromagnetic valve switches. The control circuit is used to regulate the electromagnetic valve switches, causing thin PDMS membranes to deflect pneumatically by the compressed air and generate valving and pumping effects. The micro-diagnostic chip allows for the quick detection of diseases. Compared to large-scale systems, the new microfluidic system uses smaller amounts of samples and reagents and performs fast diagnosis in an automated format. Instead of using traditional pneumatic micro-pumps, the current study adopts a new design called "spider-web" micro-pumps to increase the pumping rate, and more importantly, improve the uniformity of flow rates inside multiple micro-channels. Experimental data show that for disease diagnosis, the bio-sensing chips integrated with the micro-pneumatic valves and the peristaltic micro-pumps could successfully perform diagnosis tests. Small amounts of samples and reagents could be injected into the diagnosis chips using the micro-pumps and the micro-pneumatic valves could effectively control the movement of the samples and reagents. In order to demonstrate the functionality of the developed device, detection of hepatitis C virus (HCV) and syphilis has been performed using the bio-sampling chips. Experimental data show that fluorescence signals from the microfluidic system were comparable to the ones using conventional testing methods. The developed chip could be easily extended for multiple disease detection. The automatic bio-sensing chips could provide a useful tool for fast disease detection and be crucial for a micro-total-analysis system.

Biosensing Techniques↗
PubMed2007

Automatic segmentation and 3D reconstruction of intravascular ultrasound images for a fast preliminar evaluation of vessel pathologies.

Intravascular ultrasound (IVUS) imaging is used along with X-ray coronary angiography to detect vessel pathologies. Manual analysis of IVUS images is slow and time-consuming and it is not feasible for clinical purposes. A semi-automated method is proposed to generate 3D reconstructions from IVUS video sequences, so that a fast diagnose can be easily done, quantifying plaque length and severity as well as plaque volume of the vessels under study. The methodology described in this work has four steps: a pre-processing of IVUS images, a segmentation of media-adventitia contour, a detection of intima and plaque and a 3D reconstruction of the vessel. Preprocessing is intended to remove noise from the images without blurring the edges. Segmentation of media-adventitia contour is achieved using active contours (snakes). In particular, we use the gradient vector flow (GVF) as external force for the snakes. The detection of lumen border is obtained taking into account gray-level information of the inner part of the previously detected contours. A knowledge-based approach is used to determine which level of gray corresponds statistically to the different regions of interest: intima, plaque and lumen. The catheter region is automatically discarded. An estimate of plaque type is also given. Finally, 3D reconstruction of all detected regions is made. The suitability of this methodology has been verified for the analysis and visualization of plaque length, stenosis severity, automatic detection of the most problematic regions, calculus of plaque volumes and a preliminary estimation of plaque type obtaining for automatic measures of lumen and vessel area an average error smaller than 1mm(2) (equivalent aproximately to 10% of the average measure), for calculus of plaque and lumen volume errors smaller than 0.5mm(3) (equivalent approximately to 20% of the average measure) and for plaque type estimates a mismatch of less than 8% in the analysed frames.

Blood Vessels↗
PubMed2006

Automatic mapping of human atrial fibrillation by template matching.

BACKGROUND: The high spatiotemporal variation in morphology of fibrillation electrograms makes mapping of atrial fibrillation (AF) a difficult and burdensome task. OBJECTIVES: The purpose of this study was to evaluate the results of automatic detection of fibrillation electrograms by a template matching technique. METHODS: During cardiac surgery in 25 patients without a history of AF, paroxysms of AF were induced by rapid atrial pacing. A mapping array of 244 unipolar electrodes (3.6-cm diameter, 2.25-mm interelectrode distance) was positioned on the free wall of the right atrium. All fibrillation electrograms were correlated with a mathematically constructed library of 128 potentials of different duration, RS ratio, and short double components. The moments of maximal correlation, coinciding with the negative deflection in the fibrillation potentials, were used to create fibrillation maps. RESULTS: In each patient, a segment of 18.6 +/- 3.8 seconds of AF was analyzed, resulting in 80 to 130 maps per patient. The output of the automatic algorithm was compared with careful manual analysis by an experienced investigator. Of the total database of 398,796 fibrillation potentials, 93.6% +/- 4.2% resulted in a good correlation with one of the templates in the library (correlation coefficient >= 0.7). At a correlation threshold of 0.6, on average template matching yielded slightly more false-positive than false-negative detections (sensitivity 96.6% +/- 2.5%, positive predictive value 94.3% +/- 5.4%). The majority of false-positive detections were due to electrotonic potentials recorded along the lateral boundaries of the fibrillation waves. This led to a slight overlap of fibrillation waves but not to false detection of nonexisting wavefronts. Undersensing was mainly due to the presence of long double and fractionated potentials (2.6%) that were not represented in the template library. Fractionated parts in the electrograms were identified by failure of template matching and can be analyzed separately. CONCLUSION: Template matching is a useful technique for characterizing unipolar fibrillation electrograms and for visualizing the complex activation patterns during AF. It allows automatic evaluation of the electropathologic substrate of AF on an individual basis.

Adult↗
PubMed2005

Inducibility of abnormal automaticity and triggered activity in myocardial sleeves of canine pulmonary veins.

BACKGROUND: To study the cellular mechanisms governing cardiac atrial arrhythmias initiated by ectopic focus (or foci) from pulmonary veins (PVs). METHODS: In the present in vitro study, we applied the conventional microelectrode technique to record intracellular action potentials in PV sleeves from dogs. RESULTS: In 80 normal healthy dogs, all action potentials recorded in cardiomyocytes from PV sleeves were fast-response. The pharmacological responses to quinidine, nisoldipine, D-sotalol, 4-aminopyridine, isoproterenol, acetylcholine, and adenosine were characteristic of those in atrial cells. Diastolic depolarization and spontaneous activity could be induced by 1 mmol/L Ba2+ in all the 22 PV specimens being tested, but only in 3 of 11 of left atrial specimens (p<0.0001). In the presence of 1 mmol/L Ba2+, the diastolic slope was only slightly affected by Ni2+ (500 micromol/L), but was significantly suppressed by Cd2+ (200 micromol/L). Ryanodine (2 micromol/L) caused a transient increase, followed by a marked decrease of Ba2+-induced spontaneous activity. Isoproterenol shortened and acetylcholine prolonged the cycle length of the Ba2+-induced automatic activity. In the presence of isoproterenol, washout of acetylcholine induced a rebound phenomenon, which triggered a short period of spontaneous activity. The results suggest an important role of intracellular cytoplasmic Ca2+ loading. Under conditions that mimic ischemia/hypoxia, the resting membrane potential depolarized, upstroke of the action potential became depressed and the action potential duration shortened. In the presence of isoproterenol and elevated external K+, spontaneous activity was generated. CONCLUSIONS: These findings indicate a lack of arrhythmogenic activity in normal healthy PV sleeves. Abnormal automaticity and triggered activity occurred exclusively under simulated pathologic conditions. Ba2+-induced automaticity was more easily induced in PV than in the left atrium. The same conditions might also favor the genesis of reentry in the in vivo condition.

Action Potentials↗
PubMed2006

Who is in charge of patient safety? Work practice, work processes and utopian views of automatic drug dispensing systems.

In June 2003, a large, Canadian tertiary care facility introduced automatic drug dispensing machines on all units when it opened up a new building. In this paper, we provide an overview of the automatic drug dispensing system (ADS) implementation at the hospital. Our findings, based on daily field observations and interviews during and after implementation, with regular follow-up visits to the field site illustrate how the introduction of the ADS brought to light work practices that sometimes compromised patient safety. We suggest that utopian views of automatic drug dispensing machines obfuscate the challenges inherent to implementing such systems, and deter stakeholders from performing rigorous evaluation of the costs (both social and economic) and benefits of investing in such systems. Our work contributes to debates about the socio-technical efficacy of automating medication dispensing and delivery, and suggests that the balance of power in the patient safety equation lies in the work context and implementation issues, and not just the technology. For technology implementations to be successful considering that technologies frequently cross over jurisdictional boundaries, planning and implementation have to be conducted at a system wide level.

Canada↗
PubMed2005

Comparison of human and automatic segmentations of kidneys from CT images.

PURPOSE: A controlled observer study was conducted to compare a method for automatic image segmentation with conventional user-guided segmentation of right and left kidneys from planning computerized tomographic (CT) images. METHODS AND MATERIALS: Deformable shape models called m-reps were used to automatically segment right and left kidneys from 12 target CT images, and the results were compared with careful manual segmentations performed by two human experts. M-rep models were trained based on manual segmentations from a collection of images that did not include the targets. Segmentation using m-reps began with interactive initialization to position the kidney model over the target kidney in the image data. Fully automatic segmentation proceeded through two stages at successively smaller spatial scales. At the first stage, a global similarity transformation of the kidney model was computed to position the model closer to the target kidney. The similarity transformation was followed by large-scale deformations based on principal geodesic analysis (PGA). During the second stage, the medial atoms comprising the m-rep model were deformed one by one. This procedure was iterated until no changes were observed. The transformations and deformations at both stages were driven by optimizing an objective function with two terms. One term penalized the currently deformed m-rep by an amount proportional to its deviation from the mean m-rep derived from PGA of the training segmentations. The second term computed a model-to-image match term based on the goodness of match of the trained intensity template for the currently deformed m-rep with the corresponding intensity data in the target image. Human and m-rep segmentations were compared using quantitative metrics provided in a toolset called Valmet. Metrics reported in this article include (1) percent volume overlap; (2) mean surface distance between two segmentations; and (3) maximum surface separation (Hausdorff distance). RESULTS: Averaged over all kidneys the mean surface separation was 0.12 cm, the mean Hausdorff distance was 0.99 cm, and the mean volume overlap for human segmentations was 88.8%. Between human and m-rep segmentations the mean surface separation was 0.18-0.19 cm, the mean Hausdorff distance was 1.14-1.25 cm, and the mean volume overlap was 82-83%. CONCLUSIONS: Overall in this study, the best m-rep kidney segmentations were at least as good as careful manual slice-by-slice segmentations performed by two experienced humans, and the worst performance was no worse than typical segmentations from our clinical setting. The mean surface separations for human-m-rep segmentations were slightly larger than for human-human segmentations but still in the subvoxel range, and volume overlap and maximum surface separation were slightly better for human-human comparisons. These results were expected because of experimental factors that favored comparison of the human-human segmentations. In particular, m-rep agreement with humans appears to have been limited largely by fundamental differences between manual slice-by-slice and true three-dimensional segmentation, imaging artifacts, image voxel dimensions, and the use of an m-rep model that produced a smooth surface across the renal pelvis.

Humans↗
PubMed2005

Automatic prostate localization on cone-beam CT scans for high precision image-guided radiotherapy.

PURPOSE: Previously, we developed an automatic three-dimensional gray-value registration (GR) method for fast prostate localization that could be used during online or offline image-guided radiotherapy. The method was tested on conventional computed tomography (CT) scans. In this study, the performance of the algorithm to localize the prostate on cone-beam CT (CBCT) scans acquired on the treatment machine was evaluated. METHODS AND MATERIALS: Five to 17 CBCT scans of 32 prostate cancer patients (332 scans in total) were used. For 18 patients (190 CBCT scans), the CBCT scans were acquired with a collimated field of view (FOV) (craniocaudal). This procedure improved the image quality considerably. The prostate (i.e., prostate plus seminal vesicles) in each CBCT scan was registered to the prostate in the planning CT scan by automatic 3D gray-value registration (normal GR) starting from a registration on the bony anatomy. When these failed, registrations were repeated with a fixed rotation point locked at the prostate apex (fixed apex GR). Registrations were visually assessed in 3D by one observer with the help of an expansion (by 3.6 mm) of the delineated prostate contours of the planning CT scan. The percentage of successfully registered cases was determined from the combined normal and fixed apex GR assessment results. The error in gray-value registration for both registration methods was determined from the position of one clearly defined calcification in the prostate gland (9 patients, 71 successful registrations). RESULTS: The percentage of successfully registered CBCT scans that were acquired with a collimated FOV was about 10% higher than for CBCT scans that were acquired with an uncollimated FOV. For CBCT scans that were acquired with a collimated FOV, the percentage of successfully registered cases improved from 65%, when only normal GR was applied, to 83% when the results of normal and fixed apex GR were combined. Gray-value registration mainly failed (or registrations were difficult to assess) because of streaks in the CBCT scans caused by moving gas pockets in the rectum during CBCT image acquisition (i.e., intrafraction motion). The error in gray-value registration along the left-right, craniocaudal, and anteroposterior axes was 1.0, 2.4, and 2.3 mm (1 SD) for normal GR, and 1.0, 2.0, and 1.7 mm (1 SD) for fixed apex GR. The systematic and random components of these SDs contributed approximately equally to these SDs, for both registration methods. CONCLUSIONS: The feasibility of automatic prostate localization on CBCT scans acquired on the treatment machine using an adaptation of the previously developed three-dimensional gray-value registration algorithm, has been validated in this study. Collimating the FOV during CBCT image acquisition improved the CBCT image quality considerably. Artifacts in the CBCT images caused by large moving gas pockets during CBCT image acquisition were the main cause for unsuccessful registration. From this study, we can conclude that CBCT scans are suitable for online and offline position verification of the prostate, as long as the amount of nonstationary gas is limited.

Algorithms↗