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Biomedical subjects

R D Nawfel

Publications and source records attributed to R D Nawfel.

10 recordsLinked to original sources
PubMed2003

Safety of ERCP during pregnancy.

OBJECTIVES: There are few data in the literature regarding the indications, therapy, and safety of endoscopic management of pancreatico-biliary disorders during pregnancy. We report the largest single center experience with ERCP in pregnancy. METHODS: We reviewed 15 patients that underwent ERCP during pregnancy. In all patients, the pelvis was lead-shielded and the fetus was monitored by an obstetrician. Fluoroscopy was minimized and hard copy radiographs taken only when essential. RESULTS: The mean patient age was 28.9 yr (15-36 yr). The mean duration of gestation was 25 wk (12-33 wk); one patient was in the first, five in the second, and nine in the third trimester. The indications were gallstone pancreatitis (n = 6), choledocholithiasis on ultrasound (n = 5), elevated liver enzymes and a dilated bile duct on ultrasound (n = 2), abdominal pain and gallstones (n = 1), and chronic pancreatitis (n = 1). ERCP findings were bile duct stones (n = 6), patulous papilla (n = 1), bile duct debris (n = 1), normal bile duct and gallstones or gallbladder sludge (n = 3), dilated bile duct and gallstones (n = 1), normal bile duct and no gallstones (n = 2), and chronic pancreatitis (n = 1). Six patients underwent sphincterotomies and one a biliary stent insertion. One sphincterotomy was complicated by mild pancreatitis. All infants delivered to date have had Apgar-scores >8, and continuing pregnancies are uneventful. Mean fluorosocopy time was 3.2 min (SD +/- 1.8). An estimated fetal radiation exposure was 310 mrad (SD +/- 164) which is substantially below the accepted teratogenic dose. CONCLUSIONS: ERCP in pregnancy seems to be safe for both mother and fetus; however, it should be restricted to therapeutic indications with additional intraprocedure safety measures.

Adult↗
PubMed2000

Patient and personnel exposure during CT fluoroscopy-guided interventional procedures.

PURPOSE: To estimate patient dose and personnel exposure from phantom measurements during computed tomographic (CT) fluoroscopy, to use the estimates to provide users with dose information, and to recommend methods to reduce exposure. MATERIALS AND METHODS: Surface dose was estimated on a CT dosimetric phantom by using thermoluminescent dosimetric (TLD) and CT pencil chamber measurements. Scatter exposure was estimated from scattered radiation measured at distances of 10 cm to 1 m from the phantom. Scatter exposures measured with and without placement of a lead drape on the phantom surface adjacent to the scanning plane were compared. RESULTS: Phantom surface dose rates ranged from 2.3 to 10. 4 mGy/sec. Scattered exposure rates for a commonly used CT fluoroscopic technique (120 kVp, 50 mA, 10-mm section thickness) were 27 and 1.2 microGy/sec at 10 cm and 1 m, respectively, from the phantom. Lead drapes reduced the scattered exposure by approximately 71% and 14% at distances of 10 and 60 cm from the scanning plane, respectively. CONCLUSION: High exposures to patients and personnel may occur during CT fluoroscopy-guided interventions. Radiation exposure to patients and personnel may be reduced by modifying CT scanning techniques and by limiting fluoroscopic time. In addition, scatter exposure to personnel may be substantially reduced by placing a lead drape adjacent to the scanning plane.

Fluoroscopy↗
PubMed1999

Comparison of polytomography and computed tomography for fracture assessment.

OBJECTIVE: To compare polytomography (PT) and computed tomography (CT) for visualizing fractures and arthrodeses, with and without metal hardware, to determine whether CT could adequately replace PT. DESIGN AND PATIENTS: An ex vivo bovine model containing fractures in three planes, reduced with metal hardware, was created to compare fractures using PT and CT. The radiation dose at the skin surface was calculated for both examinations. For in vivo assessment, images of 14 patients who underwent both PT and CT (15 fractures, five arthrodeses) were coded, sorted, and independently read by four musculoskeletal radiologists. They rated the degree of certainty of their assessment. Time factors for patients and personnel and financial costs were also compared. RESULTS: In the ex vivo model the fractures were well seen on both PT and CT. The radiation dose was higher for PT than for CT. In vivo, the degree of certainty in assessment of fractures and arthrodeses was higher for PT than CT in studies in which metal hardware was present, but there was no significant difference in studies without metal hardware or in the combined (with and without hardware) studies. The patient's and technologist's time required to perform a PT examination was greater than that for CT. CONCLUSION: In the assessment of fractures and arthrodeses containing metal hardware, PT is recommended. For studies without hardware, CT is equivalent and can replace PT.

Animals↗
PubMed1999

CT fluoroscopy-guided abdominal interventions: techniques, results, and radiation exposure.

PURPOSE: To evaluate the benefits of computed tomographic (CT) fluoroscopy-guided interventions and assess radiation exposures incurred with CT fluoroscopy. MATERIALS AND METHODS: A 6-month period of use of CT fluoroscopy to guide abdominal biopsy procedures and catheter drainage was analyzed. Efficacy measures and needle placement and procedure room times were compared with those of the preceding 6 months during which conventional CT was used. CT fluoroscopic times and estimated radiation exposures were compared for two CT fluoroscopic methods. RESULTS: The sensitivity and negative predictive values for biopsy procedures and the success rate for needle aspiration or catheter drainages for CT fluoroscopy--98%, 86%, and 100%, respectively--were not significantly different from those for conventional CT--95%, 80%, and 97%, respectively. Room time was not reduced significantly, but mean needle placement time for CT fluoroscopy (29 minutes; n = 95) was significantly lower than that for conventional CT (36 minutes; n = 93; P < .005). The mean patient dose index was 74 cGy. Limiting CT fluoroscopy to scanning the needle tip rather than scanning the entire needle pass significantly reduced the dose to the patient and the operator. CONCLUSION: Although CT fluoroscopy is a useful targeting technique, significant radiation exposures may result. Therefore, radiologists need to be aware of different methods of CT fluoroscopic guidance and the factors that contribute to radiation exposure.

Abdomen↗
PubMed1994

Flattening of the contrast-detail curve for large lesions on liver CT images.

This study evaluated the relative roles of physical and perceptual factors in flattening the contrast-detail (CD) curve on liver CT scans. To estimate the role of physical factors, the theoretical CD curve for a calculated theoretical observer (i.e., a nonprewhitening matched filter) was predicted using the measured noise power spectrum and measured modulation transfer function of the CT system. Another theoretical CD curve was also produced from the output of the same calculated observer after taking the human visual response function (VRF) into account. Perceptual factors were evaluated by analyzing human observers' replicated ratings of the visibility of details super-imposed on liver CT scans. The CD curve for the calculated theoretical observer was below the CD curve actually measured for nine human observers and showed no flattening. With the VRF included, flattening of the theoretical CD curves was only produced by fixed image viewing distances of less than 30 cm, a reading style not employed by the human observers. Correlated ROC analysis of observers' replicated ratings indicated that while random, intraobserver variation was present, the magnitude of this so-called observer noise was insufficient to explain the flattening of CD curves. Use of narrow display windows did not eliminate this flattening effect. The main reason for human observers' inefficient detection of large, low contrast liver lesions appears to be a consistent misuse of the image information.

Humans↗
PubMed1991

Visualization and detection-localization on computed tomographic images.

These studies investigated observers' ability to detect and locate highly visible liver lesions on computed tomographic (CT) images, manipulating both the lesion's location and polarity (brighter or darker than liver background). Visibility of a lesion is not sufficient to guarantee accurate localization. With clinical images, possible confusions between a lesion and coexisting normal structures (like blood vessels) is a serious constraint on observer performance.

Humans↗
PubMed1988

Size discrimination in computed tomographic images. Effects of feature contrast and display window.

Studies show that features on computed tomographic (CT) images in clinical formats become less detectable when the images are produced with wider CT display windows. We studied the effects of feature contrast and the display window on observer performance in higher-order tasks that involved discriminating small size differences between features on CT images. The features to be discriminated were pairs of disks (9.0 or 9.5 mm in diameter) superimposed on CT images of water phantoms. Sets of image stimuli for two different types of size-discrimination tasks were generated with various CT contrasts specified for the superimposed features and were produced on film transparencies with display windows ranging from 90 to 2880 Hounsfield units (HU) in width. Observers' performance improved with increasing CT contrast in both size discrimination tasks. Unlike performance in feature-detection tasks, however, size discrimination was unaffected by changing the CT display window over a factor of 16 (from 90 to 1440 HU). Performance fell only at the widest display window (2880 HU), for which CT noise was essentially invisible. These results suggest that the effect of changing the CT display window may depend on the spatial frequency content of image information required for a given task.

Humans↗
PubMedDate not supplied

Contrast-detail curves for liver CT.

Contrast-detail curves were constructed for liver computed tomographic (CT) images using an objective method. Stimuli were created by superimposing disks at specified locations on sets of 92 normal liver CT images. Bright and dark disks of 9 sizes and 36 possible image contrasts were used. Sets of 92 stimuli were rendered on film at five window widths (64, 128, 256, 512, and 1024 HU). The contrast-detail (CD) curve flattened substantially for disks larger than 7-mm diameter, and its slope (on a log-log plot) was less than predicted from signal-detection theory. Manipulation of display window manipulation had little impact on this disks' visibility. The results indicate that human observers have difficulty visualizing large, low-contrast details on liver CT scans, and suggest that narrowing the display window will have little effect on this limitation.

Contrast Media↗
PubMedDate not supplied

Evaluation of video gray-scale display.

Setting up and maintaining video display monitors properly will help to reduce display variation and improve overall presentation of the radiological image. Display monitor gray-scale characteristics were examined using the SMPTE test pattern. This test pattern may be used as a standard for adjusting brightness and contrast. The controls should be adjusted to display the full dynamic range so that the 5% and 95% signal levels in the pattern are visible. Measured luminance on a laboratory workstation used for radiological perceptual experiments, and on the Siemens CT gray-scale monitor was determined to range from 0.17 to 76.0 nit, and 0.17 to 24.66 nit, respectively. These were compared with the range of approximately 17 to 514 nit for a typical film-viewbox combination. Characteristic curves were determined for both monitors, and CRT gammas were 3.34 and 2.48 for the perceptual workstation and CT console, respectively. The display gamma was determined from fitting luminance data to a log-log plot of luminance versus input gray level. The usefulness of the SMPTE test pattern for visual presentation as well as photometric measurement is demonstrated.

Computer Terminals↗