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At least 217 records · Page 12Linked to original sources
PubMed2004

Quantitative image quality evaluation of pixel-binning in a flat-panel detector for x-ray fluoroscopy.

X-ray fluoroscopy places stringent design requirements on new flat-panel (FP) detectors, requiring both low-noise electronics and high data transfer rates. Pixel-binning, wherein data from more that one detector pixel are collected simultaneously, not only lowers the data transfer rate but also increases x-ray counts and pixel signal-to-noise ratio (SNR). In this study, we quantitatively assessed image quality of image sequences from four acquisition methods; no-binning and three types of binning; in synthetic images using a clinically relevant task of detecting an extended guidewire in a four-alternative forced-choice paradigm. Binning methods were conventional data-line (D) and gate-line (G) binning, and a novel method in which alternate frames in an image sequence used D and G binning. Two detector orientations placed the data lines either parallel or perpendicular to the guide wire. At a low exposure of 0.6 microR (1.548 x 10(-10) C/kg) per frame, irrespective of detector orientation, D binning with its reduced electronic noise was significantly (p<0.1) better than the other acquisition methods. On average, alternate binning performed better than G binning. At a higher exposure of 4.0 microR (10.32 x 10(-10) C/kg) per frame, with data lines parallel to the guidewire, detection with D binning was significantly (p<0.1) better than G binning. However, with data lines perpendicular to the guidewire, G binning was significantly (p<0.1) better than D binning because the partial area effect was reduced. Alternate binning was the best binning method when results were averaged over both orientations, and it was as good as the best binning method at either orientation. In addition, at low and high exposures, alternate binning gave a temporally fused image with a smooth guidewire, an important image quality feature not assessed in a detection experiment. While at high exposure, detection with no binning was as good, or better, than the best binning method, it might be impractical at fluoroscopy imaging rates. A computational observer model based on signal detection theory successfully fit data and was used to predict effects of similar acquisition methods. Results from this study suggest the use of exposure-dependent detector binning in fluoroscopy that switches between D binning and alternate binning at low and high exposures, respectively.

Fluoroscopy↗
PubMed1994

Perception of fluoroscopy last-image hold.

Last-image hold (LIH) is used in x-ray fluoroscopy systems as a convenience and dose savings feature. In the case of an image sequence, temporal filtering in the human visual system (HVS) reduces perceived noise. In the case of a constant, single image frame, this phenomenon is not present: the image looks noisier, and low-contrast objects disappear. Using low-contrast, stationary cylinder and disk phantoms in noise, perception of single frames are compared with that of conventional 30 acq/s continuous fluoroscopy (continuous). The dose of continuous is fixed at Q/acq, and the dose of single-frame presentations is varied in order to determine an "equivalent-perception dose" for a paired-comparison task. The equivalent-perception dose depends upon the shape and size of an object. As cylinder diameter increases from 1 to 21 pixels, the equivalent-perception dose decreases from 4.6 to 2.8 Q/acq. At equal equivalent-perception dose values, the relationship between cylinder and disk diameters are determined; a cylinder diameter of 10 pixels is roughly equivalent to a disk diameter of 20 pixels. For interventional angiography, an average equivalent-perception dose of approximately 3.5 Q/acq for a single-frame presentation is predicted. Thus processing by the HVS effectively reduces noise variance by a factor of 3.5, corresponding to an effective averaging time of 3.5 frames or 120 ms. Several variance reduction techniques are suggested to create an LIH frame having perception equal to the fluoroscopy sequence.

Biophysical Phenomena↗
PubMed1994

Perceptual comparison of pulsed and continuous fluoroscopy.

Pulsed fluoroscopy (hereafter called pulsed) at reduced acquisition rates, typically 15 acq/s (pulsed-15), is proposed to reduce x-ray dose in interventional procedures. However, since the human visual system (HVS) acts as a temporal low-pass filter that interacts with such acquisitions, the proper dose for pulsed must be obtained in perception experiments. We determine the dose for low-frame-rate pulsed that gives visualization equivalent to that of conventional 30 acq/s fluoroscopy, hereafter called continuous. Computer-generated phantoms are used. They consist of stationary, low-contrast disks on a flat background containing Poisson noise that mimics quantum noise in fluoroscopy. Image sequences are displayed on the video tachistoscope, a device with considerable display flexibility. Three experimental paradigms are used. (1) In a paired-comparison study, pulsed and continuous are displayed side-by-side on the same monitor, and the visibility of a contrast detail phantom is compared. (2) Using this same display, subjects record the minimally detectable disk contrast (the min-contrast measurement). (3) In a four-alternative forced-choice experiment, a disk is placed in one of four positions, and the subject determines the position of the disk. The methods are complementary--the forced-choice experiment properly eliminates the subjectivity of the observer threshold while the paired-comparison study is much more time efficient. With regard to pulsed and continuous comparisons, remarkable similarity is found between the supra-threshold experiments (1 and 2) and the detectability experiment (3); i.e., the average absolute differences in the equivalent-perception dose as determined by the three measures is approximately 3%. No difference is found between interlaced and noninterlaced display. A relatively small dependence of dose savings on disk size is found with larger disks giving increased dose savings. Average dose savings of 22%, 38%, and 49% are found for pulsed-15, pulsed-10, and pulsed-7.5, respectively.

Fluoroscopy↗
PubMedDate not supplied

Fluoroscopy: recording of fluoroscopic images and automatic exposure control.

Some means of recording images is a necessary part of most fluoroscopic systems. Several methods are available for recording images during fluoroscopy. Screen-film recording methods such as use of spot film devices and automatic film changers provide high-spatial-resolution images. Recording images by using the image intensifier (fluorography) provides film or digital images at relatively lower doses but with poorer spatial resolution. Digitally recorded images have better contrast resolution than analog images but lower spatial resolution and represent a compromise between dose and image quality. Motion picture (cine fluorographic) recording requires extremely high dose rates compared with those of lower-resolution videotape recording of motion. Recording systems in fluoroscopy require automatic exposure control for optimum image quality. The same feedback system used to control fluorographic exposures can be used to control exposure rates during fluoroscopy as well. Automatic brightness control maintains intensifier exposure rates on the basis of subject thickness by adjusting various technique factors. The type of control mechanism depends on the imaging task and the complexity (age and cost) of the equipment. The operator can choose between better image quality (higher contrast) or lower radiation dose.

Fluoroscopy↗
PubMed1985

Videofluorography and pulsed fluoroscopy using a 512 X 512-pixel digital image system.

The combination of videofluorography and pulsed fluoroscopy using an analog videodisc system has previously been investigated with regard to image quality and potential for dose reduction. The authors found that the system could be improved still further by replacing the analog disc with a 512 X 512-pixel digital image system, thereby increasing fluoroscopic image quality and permitting stored images to be recorded with a multiformat camera. The pulsed method is compared with low-dose-rate fluoroscopy, in which a continuous image is obtained at 1/4 of the normal rate. Whereas image quality using a low dose rate was inadequate for any useful purpose, pulsed fluoroscopy was sufficient for all but the most critical stages of the examination.

Computers↗
PubMed1994

Credentialing of crossover privileges in fluoroscopy for nonradiologists.

PURPOSE: To comply with federal and state guidelines, a credentialing process was developed for nonradiologist medical users of fluoroscopy. MATERIALS AND METHODS: Seventy-three nonradiologist physicians participated in a program consisting of (a) an introductory 1-hour lecture; (b) a 10-page booklet providing basic information on radiation physics, radiobiology, and radiation safety; and (c) successful completion of a 15-question self-study quiz on fluoroscopy RESULTS: Mean fluoroscopy times per surgical case were compared for a 7-month period before (7.01 minutes in 201 cases) and after (4.39 minutes in 396 cases) the program and showed a 37.4% decrease (P < .05). Participating physician attitudes were surveyed at the completion of the program and showed an average physician time investment of 2 1/2 hours and a 4.1 approval rating for the credentialing program on a 5-point Likert scale. CONCLUSION: This fluoroscopic credentialing process for nonradiologist medical users (a) achieved a statistically significant reduction in fluoroscopic time per surgical case, (b) required a minimal investment of physician time, and (c) was well received by the medical staff.

Credentialing↗
PubMed2001

CT fluoroscopy--guided interventional procedures: techniques and radiation dose to radiologists.

PURPOSE: To determine the radiation dose to radiologists who perform computed tomographic (CT) fluoroscopic interventional procedures by using a quick-check method and a low-milliampere technique. MATERIALS AND METHODS: Two hundred twenty CT fluoroscopy--guided interventional procedures were performed in 189 patients. Procedures included 57 spinal injections, 17 spinal biopsies, 24 chest biopsies, 20 abdominal aspirations, 44 abdominal biopsies, and 58 abdominal drainages. Procedure details were prospectively recorded and included site, depth, target diameter, milliampere value, kilovolt peak, fluoroscopic time, and CT technique (continuous CT fluoroscopy, quick-check method, or a combination of these techniques). An individual collar and finger radiation detector were worn by each radiologist during each procedure to determine the dose per procedure. RESULTS: The quick-check technique was performed in 191 (87%) of 220 procedures. Four procedures were performed with continuous CT fluoroscopy, and a combination technique was used for 25 (11%) procedures. The overall mean CT fluoroscopic time was 17.9 seconds (range, 1.2--101.5 seconds). The mean milliampere value was 13.2 mA (range, 10--50 mA). The overall mean radiologist radiation dose per procedure was 2.5 mrem (0.025 mSv) (whole body). Individual procedure doses ranged from 0.66 to 4.75 mrem (0.007--0.048 mSv). The finger radiation dose was negligible. CONCLUSION: By using a low-milliampere technique and the quick-check method, CT fluoroscopic time and radiation exposure can be minimized.

Adult↗
PubMedDate not supplied

Use of fluoroscopy-guided wire manipulation and/or laparoscopic surgery in the repair of malfunctioning peritoneal dialysis catheters.

BACKGROUND: Peritoneal catheter is the lifeline for the continuous ambulatory peritoneal dialysis (CAPD) patients. Over the years, obstruction or displacement of the CAPD catheter has been one of the common complications of CAPD. Fluoroscopy-guided wire manipulation or laparoscopic surgery has been developed to manage outflow obstruction. We analyzed the catheter outcome of fluoroscopy-guided wire manipulation or laparoscopic surgery to determine the ultimate benefit of these procedures. METHODS: From June 1996 to August 2000, catheter complications were manipulated in 24 patients. Eleven (46%) of these patients were initially managed by guide wire under fluoroscopic control. The remaining 13 (54%) patients were manipulated by laparoscopic surgery. A successful outcome was defined as maintained normal peritoneal catheter function at 30 days after the manipulations. Among the catheters manipulated, 18 (75%) were inserted by nephrologist and 6 (25%) by surgeons at the initiation of CAPD. Tenckhoff double-cuff peritoneal catheters were inserted to all patients. RESULTS: The time elapsed between catheter insertion and manipulation varied from 1 to 60 days with a mean of 11 days. The primary causes of catheter malfunction were kinking in 1 case, omental wrapping with adhesions in 9 cases, and catheter displacements in the remaining 14 cases. Thirty-day catheter function was achieved in 50% (12/24) of initial catheter manipulations, with guide wire under fluoroscopic control (46%, 5/11) and laparoscopic surgery (54%, 7/13). Overall success rate of repeated manipulation was 71% (17 of 24). CONCLUSION: The successful outcome in repairing of the malfunctioning CAPD catheters could be increased by the combination of fluoroscopy-guided wire manipulation and laparoscopic surgery.

Adolescent↗
PubMed2000

Transcatheter closure of atrial septal defects without fluoroscopy: feasibility of a new method.

BACKGROUND: In an effort to reduce x-ray exposure, we developed a technique for transcatheter closure of atrial septal defects under echocardiographic guidance without fluoroscopy. To assess the efficiency of this procedure for routine use, we compared our initial results with those for the conventional procedure. METHODS AND RESULTS: Twenty-two randomly selected patients (median age 18 years; range 2 to 66 years) with atrial septal defects (n=13) or patent foramen ovale (n=9) underwent cardiac catheterization for possible interventional defect closure with echocardiography as the only imaging tool. Median stretched diameter was 9 mm (range 6 to 26 mm); median left-to-right shunt over the atrial septal defects was Qp/Qs=1.8 (range 1.5 to 2.6). An Amplatzer septal occluder was successfully implanted in 19 defects without fluoroscopy and in 3 with the help of radiography. After 1 month, complete defect closure was documented in all patients. Compared with the conventional procedure of a control group of 131 patients, procedure times were not significantly different (88 versus 100 minutes; P=0.09). However, the study group received significantly higher doses of propofol for sedation (9.9 versus 5.6 mg/kg body weight; P=0.002) owing to extended transesophageal echocardiography. CONCLUSIONS: In the majority of patients in whom transcatheter closure of interatrial communications with the Amplatzer septal occluder is possible, the procedure can be safely performed under echocardiographic guidance without fluoroscopy.

Adolescent↗
PubMed1998

Comparative study of fluoroscopy and intracardiac echocardiographic guidance for the creation of linear atrial lesions.

BACKGROUND: Recently, attempts have been made to cure atrial fibrillation by creating multiple linear atrial lesions with radiofrequency energy. Intracardiac echocardiography (ICE) offers imaging of endocardial anatomy and the ablation electrode-tissue interface not available with standard fluoroscopy. This study sought to prospectively compare fluoroscopic with ICE guidance for the creation of linear atrial lesions in a canine model. METHODS AND RESULTS: The creation of 3 linear atrial lesions was attempted in each of 10 dogs, half guided by fluoroscopy alone and half by ICE. Coil-tissue contact was prospectively graded. After ablation, animals were euthanized, and the location and continuity of lesions were evaluated. ICE guidance led to a higher percentage of successful applications (P=0.02) and mean achieved temperature (P=0. 004). The contact scores of excellent, fair, and poor correlated well with successful energy delivery, mean temperature, and efficiency of heating (P<0.0001). In 25% of the blinded energy deliveries, the location, as determined by the ablation operator, differed from that of ICE. Pathological evaluation revealed improved lesion formation in the ICE-guided compared with the ICE-blinded group. Lesions were found outside the target areas in the ICE-blinded but not the ICE-guided group. CONCLUSIONS: Compared with fluoroscopy, ICE guidance improved targeting, energy delivery, and lesion formation in this canine model. This study suggests that ICE guidance improves lesion formation and prevents energy delivery to potentially dangerous sites.

Analysis of Variance↗
PubMed1988

Transbronchial biopsy without fluoroscopy in patients with diffuse roentgenographic infiltrates and the acquired immunodeficiency syndrome.

Transbronchial biopsy with the flexible fiberoptic bronchoscope is usually performed with the assistance of fluoroscopy in order to increase diagnostic yield and decrease the incidence of pneumothorax. We have compared the results of transbronchial biopsy performed with or without fluoroscopic guidance in patients with diffuse roentgenographic infiltrates who had or were suspected of having the acquired immunodeficiency syndrome. Neither the sensitivity for Pneumocystis carinii (88.5 versus 92%) nor the percentage of patients developing pneumothoraces after transbronchial biopsy (8.6 versus 11.1%) was significantly different in those patients who had the procedure without fluoroscopic guidance compared with those in whom fluoroscopy was used. There were no patients with significant hemorrhage or deaths in either group. This complication rate compares favorably with other reports of transbronchial biopsy in immunocompromised patients in which fluoroscopy was used. "Blind" transbronchial biopsy is a safe and effective diagnostic procedure in this patient population.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Upper airway size and collapsibility in snorers: evaluation with digital fluoroscopy.

This study addressed the question of whether there are any differences in the size and collapsibility of the upper airway measured by digital fluoroscopy, between snorers and controls whilst they were awake and breathing normally; and whether there are any correlations between these measurements and other clinical data. The dynamic changes of the upper airway size were evaluated using digital fluoroscopy in 33 patients and 16 normal controls. The measurements were compared with findings in an overnight sleep study, including a static-charge-sensitive bed (SCSB) and oximeter recordings. The minimum anteroposterior dimension at the velopharyngeal level was smaller in patients with partial upper airway obstruction than in controls (p<0.005); patients with complete obstruction did not differ from the controls. The velopharyngeal airways were also more collapsible in patients with severe partial obstruction (p<0.01) than in controls. At the oropharyngeal and hypopharyngeal levels, the dimensions and the collapsibilities were similar in patients and controls. The velopharyngeal collapsibility correlated with body mass index (p<O.001), whereas the airway size did not. The velopharyngeal collapsibility was more pronounced in patients with frequent episodes of arterial oxyhaemoglobin desaturation during sleep. Velopharyngeal collapsibility associated with high body mass index was the important determinant of nocturnal breathing disturbances. Digital fluoroscopy displays the dynamic changes of the upper airways throughout the respiratory cycle.

Adult↗
PubMed1997

Hawthorne effect: shortening of fluoroscopy times during radiation measurement studies.

Screening times were recorded before (n = 92, 13 radiologists) and after (n = 75, 6 radiologists) commencing a protocol with dose-area product (DAP) measurements and filling of structured questionnaires. Fluoroscopy times were significantly (p = 0.0001) longer before starting these measurements (median 4.3, mean 5.2 min) than during them (median 3.2, mean 3.6 min), which indicates a Hawthorne effect. Fluoroscopy times did not increase during the DAP measurement period up to 21 barium enemas and a study period of up to 45 days per radiologist. Previous fluoroscopic radiation measurements based on action during an analysis period may be biased towards too short fluoroscopy times and too low doses. Radiation measurement, even if not scientifically indicated, seems a practical way of reducing doses.

Barium Sulfate↗
PubMed2004

Threshold contrast detail detectability curves for fluoroscopy and digital acquisition using modern image intensifier systems.

Threshold contrast detail detectability (TCDD) test objects are a commonly used tool to assess image quality of imaging systems. FAXIL (The Facility for the Assessment of X-ray imaging, Leeds) produced updated standard TCDD curves, for fluoroscopy systems in good adjustment, in 1992. Fluoroscopy curves can be corrected to account for the effect of image intensifier input air kerma rate and field size. This paper presents updated TCDD curves for fluoroscopy and new curves for digital acquisition. The results for digital acquisition suggest that the TCDD curves should not be corrected for input air kerma, as the quantum noise is not dominant and system noise is significant. These curves will prove useful for accepting new equipment, to give an indication of the expected image quality for a new image intensifier system.

Fluoroscopy↗
PubMed2004

Application of low dose rate pulsed fluoroscopy in cardiac pacing and electrophysiology: patient dose and image quality implications.

The performance of a low dose rate pulsed fluoroscopy option and its successful application to cardiac pacing and electrophysiology is reported. Low dose rate 6.25 frames per second pulsed fluoroscopy was made available in two catheter laboratories at a specialist cardiac centre in February 2003, and was adopted as the standard imaging technique for cardiac pacing procedures. The image quality was found to be considerably poorer than conventional modern units, being very similar to that which would have been accepted as adequate performance 20 years ago, but at less than one-tenth of the dose rate. No problems with the clinical acceptance of this imaging mode for cardiac pacing and electrophysiology have been reported. The already low median patient dose-area product for pacing at this cardiac centre was further reduced by 50% with the introduction of this fluoroscopy option.

Attitude of Health Personnel↗
PubMed1994

Model for perception of pulsed fluoroscopy image sequences.

Pulsed fluoroscopy at reduced frame rates can be used to lower x-ray dose with equivalent detection (hereafter called equivalent perception) of low-contrast, stationary objects. Experimentally average dose savings of 22%, 38%, and 49%, for pulsed fluoroscopy at 15, 10, and 7.5 acquisitions per second, respectively, are documented. Dose savings depend on object size, with fewer savings for smaller objects. To explain these data, we extend the framework of an ideal observer with three models for the spatiotemporal response of the human visual system (HVS). They are model 1, separable; model 2, nonseparable; and model 3, nonseparable with internal observer noise. With no free parameters, model 1 predicts the average dose savings within a 3% difference but does not describe the effect of object size. Models 2 and 3 explain the influence of size, and model 3, with a single free parameter, fits the measurements best. Perception of pulsed fluoroscopy is thus well described in terms of spatiotemporal processing by the HVS.

Fluoroscopy↗
PubMed2001

CT fluoroscopy guidance for transbronchial needle aspiration: an experience in 35 patients.

OBJECTIVE: To demonstrate the usefulness of real-time guidance with CT fluoroscopy to improve the yield of transbronchial needle aspiration (TBNA). DESIGN: Prospective, observational. SETTING: A tertiary-care, university-affiliated medical center. METHODS: From December 1998 to April 2000, 35 patients underwent CT fluoroscopy-guided TBNA. Patients with subcarinal and precarinal lymph nodes were only included if a previous attempt was nondiagnostic, as the initial yield in this setting with conventional TBNA is high. TBNA was performed using standard technique in a CT-scan suite. Needle location was confirmed with fluoroscopy without IV contrast being used. Specimens were evaluated on-site for adequacy. RESULTS: The procedure had to be aborted in three patients before TBNA could be performed. Samples were obtained in 32 patients. Samples were nondiagnostic in four patients. Adequate tissue was obtained in 28 of 32 patients (87.5%). Twenty-two patients had a specific benign or malignant diagnosis made, and 6 patients had lymphocytes only on the specimen. In follow-up, only one of these six patients proved to have a malignancy. All procedures were performed within a regular interventional CT time slot of 1 h. No TBNA side effects were noted. CONCLUSION: TBNA under CT fluoroscopic guidance is easy to perform. The yield in all accessible lymph node stations is high.

Adult↗
PubMed1988

Transbronchial biopsy without fluoroscopy. A seven-year perspective.

The use of fluoroscopic guidance for transbronchial biopsy (TBB) during flexible fiberoptic bronchoscopic examination has been controversial. Patient records and bronchoscopy reports for 112 transbronchial biopsies performed with fluoroscopy over a seven-year period were reviewed and compared with those of 135 transbronchial biopsies performed without fluoroscopy over the same interval. Complication rates with regard to pneumothorax, fever, and hemorrhage were compared, as were yield data for neoplasm, sarcoidosis, and other miscellaneous pulmonary diagnoses. Complication rates were low in both groups and not statistically different; yield data were likewise comparable, particularly in diffuse neoplasm and sarcoidosis. This report suggests that TBB without fluoroscopy (in the basilar segments) is safe and that diagnostic yield, particularly in sarcoidosis and diffuse neoplasm, is good.

Biopsy↗