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Biomedical subjects

K D Hopper

Publications and source records attributed to K D Hopper.

134 records · Page 8Linked to original sources
PubMedDate not supplied

The effect of helical CT on X-ray attenuation.

PURPOSE: Conventional CT has been shown to have wide variability in measured CT attenuation, both temporally within the same scanner and between different scanners. Many radiologists have raised the concern that the increased noise and multiple variables associated with helical CT may lead to degradation in resolution, specifically causing errors in CT number values. This study was designed to specifically evaluate the performance of both types of CT scanning in this regard. METHOD: A Picker PQ2000 helical CT scanner was used to scan a phantom containing multiple tissue-equivalent densities, allowing the measurement of CT attenuation of soft tissue, distilled water, cortical bone, medullary bone, air, and fat with a variety of techniques. A Catphan phantom was imaged with a variety of slice thicknesses (2, 4, and 8 mm), phantom positions (isocenter, y = +20 cm), and pitches (1.0, 1.5, 2.0) using both conventional and helical sequences. The entire image set was repeated with two additional annuli placed around the Catphan phantom to simulate the abdomen and the calvarium. The attenuation measurements of the same imaging parameters for helical versus conventional CT were statistically compared. RESULTS: No statistical differences were found for the CT numbers based on scan type (conventional versus helical) for all sequences and gantry positions tested, including helical CT with pitches > 1.0. Greater CT number variability was found with the extremes of tissue density such as with air and especially cortical bone, but were not statistically significant. The addition of the abdominal and calvarial annuli created a greater variation in CT attenuation values, but again were not statistically significant. CONCLUSION: The measurement of X-ray attenuation does not vary significantly with the use of the helical technique.

Adipose Tissue↗
PubMedDate not supplied

Multiplanar image reconstruction and 3D imaging using a musculoskeletal phantom: conventional versus helical CT.

PURPOSE: Our goal was to perform a detailed comparison of the relative performances of helical CT (pitches 1.0, 1.5, and 2.0) and conventional (overlapped and nonoverlapped) CT in detailed 3D and MPR musculoskeletal imaging. METHOD: A specially designed bone fragment phantom was imaged with multiple slice thicknesses using conventional (overlapped and nonoverlapped) and helical (varying pitch and slice index) CT. Studies were randomized, blinded, and graded using predetermined criteria by 10 radiologists. Statistical analysis included an assessment of raw image scores, a separate testing using duplicate copies of the conventional images as gold standards, and a multivariate model based upon the results of both scoring systems. RESULTS: When assessing raw scores of the images, conventional scans were consistently scored more favorably than helical studies. Decreasing the slice index improved conventional CT studies and helical studies with a pitch of 1.0, but showed no effect on helical studies with a pitch of > 1.0. When using the conventional studies as gold standards, the helical studies were consistently graded as poorer than conventional overlapped and nonoverlapped studies. CONCLUSION: For detailed musculoskeletal 3D and MPR work, helical CT may not adequately compare with conventional CT and offers no discernible advantage, particularly for pitches of > 1.0.

Bone and Bones↗
PubMedDate not supplied

The optimization of helical thoracic CT.

PURPOSE: Our purpose was to determine the optimal helical thoracic CT scanning protocol. METHOD: Three adult Suffolk sheep under general anesthesia were repeatedly scanned by a variety of variable thickness helical and conventional plus thin section high resolution (lung gold standard) CT sequences, reconstructed for mediastinal (standard interpolator and algorithm) and lung parenchymal (extrasharp interpolator, bone algorithm) detail. The images were evaluated in a random order by five separate blinded, experienced imagers utilizing a predetermined grading scale. RESULTS: At equivalent slice thicknesses, the mediastinal images showed no statistically significant differences between conventional and helical CT using pitches of 1.0, 1.5, and 2.0. However, the 5-mm-thick sections, regardless of technique, performed better than did either the 2- or the 10-mm-thick section images. For the lung interstitium, there was an obvious and marked advantage to reconstructing the lung images separately from the mediastinal images with edge-enhancing algorithms and interpolators. With 1-mm-high mA thin section, high resolution lung CT as the gold standard, 2 mm conventional and helical pitch 1.0, 1.5, and 2.0 images were all graded equivalent. Of the 5 mm images, the helical pitches of 1.0 and 1.5 were graded equivalent to the gold standard. All of the 10 mm lung sections using both conventional and helical CT were graded statistically worse than the gold standard (p < 0.05). CONCLUSION: The use of helical CT with a 5 mm beam collimation and a pitch of 1.0 or 1.5 reconstructed twice to maximize both the mediastinal and the lung parenchymal detail provides the optimal way to routinely evaluate the chest.

Algorithms↗
PubMedDate not supplied

The feasibility of surgical site tagging with CT virtual reality of the paranasal sinuses.

PURPOSE: The purpose of this work was to evaluate the feasibility of tagging (highlighting) surgical sites using volumetric CT virtual reality of the paranasal sinuses in the planning for endoscopic sinus surgery. METHOD: Twenty-five patients with significant paranasal sinus disease had a planned surgical site marked on 2D coronal images. This planned surgical site was then tagged and included on CT volumetric virtual reality imaging. Each case was evaluated as to the ability of the CT virtual reality to demonstrate the planned surgical site and its orientation with respect to adjacent superficial anatomy. RESULTS: For all 25 planned surgeries, the virtual images showed the entire surgical site marked on the 2D coronal images. In all 25 cases, the orientation of the planned surgical site to adjacent normal anatomy was well demonstrated. For surgery into the maxillary sinuses, tagging and electronic removal of the middle turbinates and uncinate processes mimicked the actual surgery and allowed complete visualization of the infundibulum and the planned surgical site. CONCLUSION: Planned endoscopic paranasal sinus surgical sites can be easily and reliably highlighted using CT virtual reality techniques with respect to the patient's normal endoscopic anatomy.

Data Display↗
PubMedDate not supplied

The use of clinical CT for baseline bone density assessment.

PURPOSE: Many patients having an abnormal initial bone densitometry study have had a previous abdominal/pelvic computed tomography (CT) for other clinical reasons. This study evaluates if a nondedicated quantitative CT (QCT) abdominal/pelvic CT scan could be used as reliable baseline data for subsequent dedicated bone density studies. SUBJECTS AND METHODS: Twenty-six patients (13 men, 13 women) undergoing clinically-indicated non-i.v. and i.v. contrast abdominal/pelvic CT had dedicated QCT performed immediately following scans of the L1, L2, and L3 vertebral bodies. QCT was then performed on all three scans. A repeated measures analysis of variance model was used to analyze the data in order to compare noncontrast clinical CT with QCT and noncontrast clinical with contrast clinical CT. RESULTS: The mean bone mineral density for the noncontrast clinical study was 98.51 (mg/cc) versus 90.56 (mg/cc) for QCT (p = 0.0003; 95% confidence interval: 3.90 to 13.71). There was no significant difference (p = 0.085) between QCT performed from non-i.v. and i.v. contrast clinical CT scans. CONCLUSION: Bone densitometry can be performed from either non-i.v. or i.v. contrast clinical CT scans if a conversion factor is applied. This can be determined by utilizing a formula Daverage = -7.83 + (0.99 x NCaverage), where Daverage and NCaverage are the abbreviations of "dedicated" and "noncontrast clinical" BMD averaged over vertebral bodies L1-L3, respectively.

Adult↗
PubMedDate not supplied

Radioprotection to the eye during CT scanning.

BACKGROUND AND PURPOSE: The lens of the eye is sensitive to radiation. Children undergoing CT of the head and patients undergoing repeated CT scanning of the head are vulnerable to this complication. The purpose of this study was to test the ability of a heavy metal, bismuth, in reducing radiation to the lens of the eye during routine cranial CT. METHODS: Both phantom and human studies were done. Using a standard head-attenuating phantom, scanning was performed with detectors placed over the eye, first without the protectors, and then with shielding by one (1T), two (2T), or three thickness (3T) of bismuth-coated latex. The patient study included 30 patients randomized into one of three groups with eye protection provided by 1T, 2T, or 3T of the bismuth-coated latex. Control measurements were done using thermoluminescent dosimeters over the forehead above each eye. Image artifact from the bismuth shields was assessed. RESULTS: The phantom study demonstrated that the use of bismuth-coated shielding over the eyes decreased radiation dosage by 48.5%, 59.8%, and 65.4% using 1T, 2T, and 3T, respectively. The effect of eye shielding in decreasing radiation dosage to the eye was highly significant for all three thicknesses (P = 2.9 x 10(-81) to 1.9 x 10(-89)). In the patient study, the use of 1T, 2T, and 3T of bismuth-coated latex saved an average radiation dose of 39.6%, 43.5%, and 52.8%, respectively. While the use of shielding was statistically significant in saving radiation for all thicknesses (P = 2.2 x 10(-10) to 1.4 x 10(-21)), there was no statistical difference between 1T, 2T, and 3T of bismuth-coated latex shielding found in patients. However, the trend was for increased radiation savings to the eye with increased thickness of shielding used. A review of all 30 studies showed no significant artifact caused by the eye shielding, regardless of thickness. CONCLUSION: Bismuth-coated latex shielding of the eye during cranial CT is simple to apply, inexpensive, and causes up to a 50% reduction in radiation to the lens of the eye.

Adult↗
PubMedDate not supplied

The interventricular extension of choroid plexus papillomas.

Four cases of choroid plexus papilloma extending through the foramen of Monro are presented. All four patients were evaluated by contrast-enhanced CT and two of these were also evaluated by neurosonography. No other intraventricular tumor commonly extends through a ventricular outlet. The radiographic demonstration of this extension of an intraventricular mass through the foramen of Monro, cerebral aqueduct, or foramen of Luschka or Magendie represents an ancillary diagnostic sign of choroid plexus papilloma.

Cerebral Ventricle Neoplasms↗