Biomedical subjects

C H McCollough

Publications and source records attributed to C H McCollough.

12 recordsLinked to original sources

PubMed1996

Detection of colorectal polyps by computed tomographic colography: feasibility of a novel technique.

BACKGROUND & AIMS: Computed tomographic colography (CTC) represents a novel technique for colorectal polyp detection. A prospective study was undertaken to determine the optimal CTC scanning parameters based on an artificial colon model and to assess the feasibility of CTC to detect clinically significant colorectal polyps. METHODS: A colon model was scanned by helical computed tomography at multiple parameters. Reformatted two-dimensional and three-dimensional images were then graded for polyp detection and image quality. Subsequently, 10 patients with known colon polyps underwent CTC immediately before colonoscopy. The number of polyps detected by two radiologists using CTC were compared with colonoscopy results that served as the gold standard. RESULTS: The optimal scanning parameters in the colon model were 5-mm collimation, 5 mm/s table speed, and 1-mm reconstruction interval. Ten patients had 30 polyps (range, 0.2-2.0 cm) by colonscopy, and all polyps > or = 0.5 cm were adenomas. Polyp detection by CTC for both observers was 100% (5 of 5) > or = 1 cm, 71% (5 of 7) between 0.5 and 0.9 cm, and 11%-28% (2-5 of 18) < 0.5 cm. CONCLUSIONS: Based on this small, unblinded pilot study, CTC is feasible for colorectal polyp detection > or = 0.5 cm in diameter.

Aged↗

PubMed1996

Technical exhibits.

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Exhibitions as Topic↗

PubMed1995

Breast dose during electron-beam CT: measurement with film dosimetry.

PURPOSE: To measure the breast dose and dose distribution from examinations performed with electron-beam computed tomography (CT). MATERIALS AND METHODS: Radiographic film was placed bilaterally at three depths in the breasts of an anthropomorphic phantom and exposed with clinically relevant protocols. The average breast dose and the dose distribution were obtained from the digitized and calibrated film and compared with those obtained with conventional CT. RESULTS: Breast doses from electron-beam CT chest, coronary artery calcium, and cardiac function examinations were 21.9, 2.87, and 1.55 mGy, respectively. Within the breast, the dose decreased linearly by a factor of three from the axilla to the sternum. The breast dose from a conventional CT chest examination ranged from 18 to 33 mGy and did not vary substantially across the breast. CONCLUSION: For chest examinations, the average breast dose from an electron-beam CT scanner was comparable to that from conventional CT scanners, despite the differences in dose distribution.

Breast↗

PubMed1995

Electron-beam CT: use of a calibration phantom to reduce variability in calcium quantitation.

PURPOSE: To measure scanner and patient variation in computed tomographic (CT) numbers for electron-beam CT and to determine the ability of calibration phantoms to reduce variability in calcium quantitation. MATERIALS AND METHODS: Two calibration phantoms were imaged to ensure longitudinal homogeneity and to determine the short-term intrascanner variation in CT numbers. Each phantom set was imaged twice a day for 14 weeks to determine intra- and interscanner variation. Data from examinations of 167 patients that included the phantom were analyzed to determine the intra- and interpatient variation in CT numbers of objects with known calcium concentrations. RESULTS: The calibration reduced scanner variations by approximately 25%. The calcium concentration associated with a CT number of 130 HU varied from 77.1 to 136.4 mg/cm3 and was dependent on patient girth, sex, smoking history, and image level. CONCLUSION: Scanner and patient variations in CT numbers in electron-beam CT can be reduced with a calibration phantom. In vitro and in vivo estimates of calcium concentration had a precision of 2% and 7%, respectively.

Adult↗

PubMed1994

The measurement of radiation dose profiles for electron-beam computed tomography using film dosimetry.

The unique geometry of electron-beam CT (EBCT) scanners produces radiation dose profiles with widths which can be considerably different from the corresponding nominal scan width. Additionally, EBCT scanners produce both complex (multiple-slice) and narrow (3 mm) radiation profiles. This work describes the measurement of the axial dose distribution from EBCT within a scattering phantom using film dosimetry methods, which offer increased convenience and spatial resolution compared to thermoluminescent dosimetry (TLD) techniques. Therapy localization film was cut into 8 x 220 mm strips and placed within specially constructed light-tight holders for placement within the cavities of a CT Dose Index (CTDI) phantom. The film was calibrated using a conventional overhead x-ray tube with spectral characteristics matched to the EBCT scanner (130 kVp, 10 mm A1 HVL). The films were digitized at five samples per mm and calibrated dose profiles plotted as a function of z-axis position. Errors due to angle-of-incidence and beam hardening were estimated to be less than 5% and 10%, respectively. The integral exposure under film dose profiles agreed with ion-chamber measurements to within 15%. Exposures measured along the radiation profile differed from TLD measurements by an average of 5%. The film technique provided acceptable accuracy and convenience in comparison to conventional TLD methods, and allowed high spatial-resolution measurement of EBCT radiation dose profiles.

Electrons↗

PubMed1994

Technical exhibits.

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Diagnostic Imaging↗

PubMed1994

Small lesions in the heart identified at electron beam CT: calcification or noise?

PURPOSE: To identify a minimum definition of coronary artery calcification (CAC) at electron beam computed tomography (CT) that would give repeatable results and be accurate as a marker for coronary artery disease. MATERIALS AND METHODS: Hyperattenuating (> 130 HU) foci 0.69-3.09 mm2 in area were evaluated for 256 subjects who underwent two sequential electron beam CT examinations to determine the percentage of hyperattenuating foci seen on a first examination that were seen again on a second examination. Accuracies of varying minimum definitions of CAC were determined in 160 subjects who underwent electron beam CT and coronary arteriography. RESULTS: Hyperattenuating foci more than 2 mm2 in area were seen again at a second examination in more than 50% of cases (P < .0001). At this minimum definition of CAC, the sensitivity and specificity for identifying any angiographically defined coronary artery disease were 82% and 85%, respectively. CONCLUSION: The 2-mm2-area definition of CAC was reliable and provided an accurate indication of coronary artery disease.

Adult↗

PubMed1994

Radiation dosimetry for electron beam CT.

PURPOSE: To measure the radiation dose profile, multiple-scan average dose (MSAD), and computed tomography dose index (CTDI) for electron beam CT and to determine the accuracy of ionization-chamber and manufacturer estimates of patient dose. MATERIALS AND METHODS: High-resolution dose profiles along the longitudinal axis were acquired at several positions within the scan plane with use of radiographic film. The full-width-at-half-maximum values, peak radiation dose, CTDI, and MSAD were calculated from the digitized film profiles. CTDI was also measured with an ionization chamber. RESULTS: The full-width-half-maximum value of the radiation profiles were significantly wider than the nominal scan width for the 6-mm single-section and 8-mm multisection modes. In the single-section mode, the CTDI underestimated the MSAD by 15%-30%. The multisection radiation profile was nonuniform and asymmetric. CONCLUSION: Patient doses in electron beam CT are approximately 125% of the ionization-chamber CTDI measurements in the single-section mode. For the multisection mode, the average patient dose over the scan volume is approximately 70%-85% of the ionization-chamber CTDI measurements.

Humans↗

PubMed1994

The technical design and performance of ultrafast computed tomography.

The ultrafast radiograph CT scanner utilizes a scanning electron beam and semicircular tungsten targets to produce a moving radiograph source about the patient, thus eliminating mechanical motion within the gantry. This design allows scan times as short as 50 or 100 ms, as well as two levels of image resolution. The short scan time reduces the effects of motion blurring and artifacts and provides the ability to obtain high-quality images of dynamic processes and rapidly moving organs. When utilized in the SS (high-resolution) mode, the UFCT scanner provides contiguous image acquisition through a patient volume at rapid speeds, yet maintains image quality comparable with conventional CT scanners. This technology provides extremely short exposure times, rapid acquisition of multiple slices, continuous scanning without concern for anode heat storage and dissipation, and the ability to image moving organs or flowing contrast media. Many clinical applications exist that exploit these unique features.

Heart Diseases↗

PubMed1993

Densitometric assessment of regional left ventricular systolic function during graded ischemia in the dog by use of dual-energy digital subtraction ventriculography.

Densitometric analysis of images obtained by digital subtraction angiography (DSA) allows for more reproducible and less operator-dependent quantitation of ventricular function. Conventional DSA uses temporal subtraction but is limited by misregistration artifacts. Dual-energy digital subtraction angiography (DE-DSA) is immune to such misregistration artifacts. The ability of DE-DSA to quantitate changes in regional ventricular volume resulting from ischemia was tested. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images was used to quantitate regional left ventricular systolic function during four levels of ischemia ranging from mild to severe in open-chest dogs (n = 10). DE-DSA left ventriculograms were obtained by means of central venous injections of iodinated contrast medium. Ischemia was graded according to percentage of systolic wall thickening as measured by sonomicrometry. Phase-matched end-systolic images were obtained at each of four levels of ischemia by subtracting an end-systolic control image from each end-systolic ischemic image. Ejection fraction images were obtained at the control level and at each level of ischemia by subtracting an end-systolic image from an end-diastolic image of the same cardiac cycle. The resulting wall motion difference signals represent the changes in regional ventricular volumes and were quantitated by densitometry. Densitometry was able to detect the effect of all levels of ischemia on regional function, even the mildest. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images provides a sensitive technique for detecting and quantitating the changes in regional left ventricular systolic volume that occur with ischemia.

Angiography, Digital Subtraction↗

PubMedDate not supplied

An electron-beam CT approach for transvenous coronary arteriography.

OBJECTIVE: The goal is to image the 3D anatomy of the major coronary arteries within a single breath-hold and using a single intravenous injection of contrast agent. MATERIALS AND METHODS: With use of an electron-beam CT (EBCT) scanner, operated in its multislice scan mode (using all four target rings, each scanning two nominal 8 mm thick slices in a total time interval of 224 ms), a radiologically realistic thorax phantom containing a heart with coronary arteries (opacified with 40 mg iodine/ml) was scanned six times with the patient table advanced by a 2 mm step into the scanner between each scan. The normalized and scaled sinogram data were transferred to an off-line computer and reconstructed using our own implementation of a 3D algebraic reconstruction technique that takes into account the exact 3D relationship of the X-ray source and detector elements of the EBCT. RESULTS: A single volume image consisting of 40 slices, at 2 mm intervals and each uniformly 3.7 mm thick, depicted the lumina of the coronary arteries with greater anatomic detail than the "original" images at 8 mm, primarily because of the reduced partial volume effect. CONCLUSION: Our preliminary results suggest that EBCT, operated in multislice scan mode, may be useful for transvenous coronary angiography performed within a single breath-hold.

Coronary Angiography↗

PubMedDate not supplied

A correlated noise reduction algorithm for dual-energy digital subtraction angiography.

It has long been recognized that the problems of motion artifacts in conventional time subtraction digital subtraction angiography (DSA) may be overcome using energy subtraction techniques. Of the variety of energy subtraction techniques investigated, non-k-edge dual-energy subtraction offers the best signal-to-noise ratio (SNR). However, this technique achieves only 55% of the temporal DSA SNR. Noise reduction techniques that average the noisier high-energy image produce various degrees of noise improvement while minimally affecting iodine contrast and resolution. A more significant improvement in dual-energy DSA iodine SNR, however, results when the correlated noise that exists in material specific images is appropriately cancelled. The correlated noise reduction (CNR) algorithm presented here follows directly from the dual-energy computed tomography work of Kalender who made explicit use of noise correlations in material specific images to reduce noise. The results are identical to those achieved using a linear version of the two-stage filtering process described by Macovski in which the selective image is filtered to reduce high-frequency noise and added to a weighted, high SNR, nonselective image which has been processed with a high-frequency bandpass filter. The dual-energy DSA CNR algorithm presented here combines selective tissue and iodine images to produce a significant increase in the iodine SNR while fully preserving iodine spatial resolution. Theoretical calculations predict a factor of 2-4 improvement in SNR compared to conventional dual-energy images. The improvement factor achieved is dependent upon the x-ray beam spectra and the size of blurring kernel used in the algorithm.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗