Optimization of shaded surface display for CT angiography.

RATIONALE AND OBJECTIVES: The authors performed this study to determine the optimum threshold for performing computed tomographic (CT) angiography with shaded surface display (SSD). MATERIALS AND METHODS: A dedicated phantom was developed with an 8-mm luminal diameter. Each of 19 vessels had stenoses ranging from 0% to 93.8%. Five blinded, experienced reviewers separately measured each vessel by using SSD with display thresholds of 50, 100, 150, and 200 HU. RESULTS: For vessel diameters of 2 mm and larger, the best threshold value was 100 HU. This yielded measurements within 2% of the actual diameter and produced no false occlusions. For vessels 1 mm in diameter, the best threshold remained 100 HU, but this threshold was significantly less accurate than the standard (P = .0001) and produced two false occlusions in 15 vessels. For vessels 0.5 mm in diameter, the best threshold was 50 HU, although this still produced measurements significantly less accurate than the gold standard (P = .036) and one false occlusion in 15 vessels. CONCLUSION: CT angiography with SSD and an optimized threshold value is a useful technique in vessels 1 mm and larger.

CT angiography: in vitro comparison of five reconstruction methods.

OBJECTIVE: Five image reconstruction techniques have been used with CT angiography: axial (cross-sectional), maximum intensity projection (MIP), curved multiplanar reconstruction (MPR), shaded-surface display, and volume rendering. This study used a phantom to compare the accuracy of these techniques for measuring stenosis. SUBJECTS AND METHODS: A 19-vessel phantom containing various grades of concentric stenoses (0-100%) and three lengths (5, 7.5, and 10 mm) of stenoses was used for this study. Scans were obtained with a slice thickness of 2.0 mm, slice interval of 1.0 mm, pitch of 1.0, 120 kVp, 200 mA, and with the vessels oriented parallel to the z-axis and opacified with nonionic contrast material. CT angiography images were produced using five optimized techniques: axial, MIP, MPR, shaded-surface display, and volume rendering; and measurements were made with an electronic cursor in the normal lumen and mid stenosis by five separate investigators who were unaware of vessel and stenosis diameters. Each of the techniques was first optimized according to the radiology literature and our own preliminary testing. RESULTS: For vessels greater than 4 mm in diameter, axial, MIP, MPR, shaded-surface display, and volume-rendering CT angiography techniques all had a measurement error of less than 2.5%. However, axial, MIP, MPR, and shaded-surface display techniques were less accurate in estimating smaller (

Training in obstetric sonography for radiology residents and fellows in the United States.

OBJECTIVE: The purpose of our study was to assess the current experience of radiology residents and fellows in obstetric sonography. SUBJECTS AND METHODS: Written surveys were sent to the directors of 206 accredited radiology residency programs and 85 fellowship programs in the United States. The surveys encompassed obstetric sonographic experience during routine working hours and after hours, the level of supervision, the types of scanning performed, and the extent of formal lectures available during training. Additional questions concerned the relative knowledge of laboratory accreditation processes and training of faculty covering obstetric sonography. RESULTS: Sixty (29%) of 206 accredited radiology residency programs and 24 (28%) of 85 fellowship programs returned surveys. The experience among residency programs was similar, providing fewer than 4 weeks per year of obstetric sonography, usually within their own department of radiology. Residents were more likely to be sent to outside departments for second or third trimester sonography experience. A decrease in scanning assistance was reported for examinations performed after hours, more so for second or third trimester studies. Lecture topics revealed similar deficiencies for residency and fellowship programs. CONCLUSION: Greater emphasis on the performance of prenatal sonographic examinations may be warranted during formal sonography rotations. Current levels of experience in obstetric sonography may not be providing sufficient experience to allow residents to appropriately manage call cases or for practicing radiologists to provide such services after their training is completed.

Comparative assessment of CT and sonographic techniques for appendiceal imaging.

OBJECTIVE: We performed a comparative assessment of CT and sonographic techniques used to assess appendicitis. MATERIALS AND METHODS: One hundred patients with clinically suspected acute appendicitis were examined with sonography, unenhanced focused appendiceal CT, complete abdominopelvic CT using IV contrast material, focused appendiceal CT with colonic contrast material, and repeated sonography with colonic contrast material. Each sonogram was videotaped for subsequent interpretation by three radiologists and two sonographers. The mean sensitivity, specificity, positive and negative predictive values, inter- and intraobserver variability, and diagnostic confidence scores of all observers were used for comparative performance assessments. The three CT examinations were filmed and interpreted separately by four radiologists. Patient discomfort was assessed on a 10-point scale for each radiologic study. Diagnoses were confirmed by pathologic evaluation of resected appendixes or clinical follow-up for a minimum of 3 months after presentation. RESULTS: Twenty-four of the 100 patients had positive findings for acute appendicitis. Both sonographic techniques had high specificity (85-89%) and comparable accuracy (73-75%) but low sensitivity (33-35%) and inter- and intraobserver variability (kappa = 0.15-0.20 and 0.39-0.42, respectively). Unenhanced focused appendiceal CT, abdominopelvic CT, and focused appendiceal CT with colonic contrast material all significantly outperformed sonography (p <0.0001), with sensitivities of 78%, 72%, and 80%; specificities of 86%, 91%, and 87%; and accuracies of 84%, 87%, and 85%, respectively. Abdominopelvic CT gave the greatest confidence in cases with negative findings (p = 0.001), and focused appendiceal CT with colonic contrast material gave the greatest confidence for cases with positive findings (p = 0.02). In terms of inter- and intraobserver variability, focused appendiceal CT with colonic contrast material yielded the highest, and unenhanced focused appendiceal CT the lowest, agreement (interobserver kappa = 0.45 vs. 0.36 and intraobserver kappa = 0.85 vs. 0.76, respectively) (p <0.05). Colonic contrast material was unsuccessfully advanced into the cecum in 18% of patients and leaked in another 24%. Patient discomfort was greatest with focused appendiceal CT using colonic contrast material and least with unenhanced focused appendiceal CT (p <0.05). CONCLUSION: A standard abdominopelvic CT scan is recommended as the initial examination for appendicitis in adult patients. However, focused appendiceal CT with colonic contrast material material should be used as a problem-solving technique in difficult cases.

Mucosal detail at CT virtual reality: surface versus volume rendering.

PURPOSE: To evaluate computed tomographic virtual reality with volumetric versus surface rendering. MATERIALS AND METHODS: Virtual reality images were reconstructed for 27 normal or pathologic colonic, gastric, or bronchial structures in four ways: the transition zone (a) reconstructed separately from the wall by using volume rendering; (b) with attenuation equal to air; (c) with attenuation equal to wall (soft tissue); (d) with attenuation halfway between air and wall. The four reconstructed images were randomized. Four experienced imagers blinded to the reconstruction graded them from best to worst with predetermined criteria. RESULTS: All readers rated images with the transition zone as a separate structure as overwhelmingly superior (P <.001): Nineteen cases had complete concurrence among all readers. The best of the surface-rendering reconstructions had the transition zone attenuation equal to the wall attenuation (P <.001). The third best reconstruction had the transition zone attenuation equal to the air attenuation, and the worst had the transition zone attenuation halfway between the air and wall attenuation. CONCLUSION: Virtual reality is best with volume rendering, with the transition zone (mucosa) between the wall and air reconstructed as a separate structure.

CT bronchoscopy: optimization of imaging parameters.

The authors evaluated the relative importance of the following scanning parameters at computed tomographic bronchoscopy in an anesthetized adult sheep's thorax: section thickness (2, 4, 8 mm), pitch (1.0, 1.5, 2.0), milliampere setting (100, 175, 250 mA), and overlap of reconstructed sections (0%, 25%, 50%, 75%). Five blinded readers ranked the images twice in comparison with photographs of the mounted specimen. Differences in image quality were significant (P < .001) with section thickness of 2 mm and a pitch of 1.0. The milliampere setting had only a minor effect on image quality, and a 50% overlap of reconstructed sections was best.

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.

Utility of low mA 1.5 pitch helical versus conventional high mA abdominal CT.

The objective of this study was to evaluate the utility of a low mA 1.5 pitch helical versus conventional high mA conventional technique in abdominal computed tomography (CT). Twenty-five patients who had both a conventional high mA (> 300) and a 1.5 pitch low mA (80-125) helical CT within 3 months were selected for inclusion in the study. Patients were excluded who had a significant change in pathology between the two studies. The other parameters (injection rate, contrast type and volume, and filming window/level) were constant. The studies were randomized and blinded to five separate experienced readers who graded the studies by a variety of normal anatomical structures and pathological criteria. Overview questions also assessed noise, resolution, contrast, and overall quality. The abdominal wall/retroperitoneum and hiatal hernias were statistically better visualized on the conventional high mA studies. However, for all other normal anatomical and pathological sites, there was equivalent or better visualization on the helical versus the conventional CT examinations. The resolution of the helical studies was graded statistically better than the high mA conventional CT scans as was the amount of noise present on the images. While there was some advantage for conventional high mA CT with respect to contrast enhancement and low contrast sensitivity, these differences were not statistically significant. It appears from the data of this study that a low mA technique in evaluating the abdomen may be a useful option in performing routine abdominal CT. The radiation dose savings to the patient is significant and there appears to be little degradation of image quality using a low mA 1.5 helical versus mA conventional CT technique.

Extended pitch thoracic helical CT 47.

The objective of this study was to test whether extended 1.5 pitch helical computed tomography (CT) can be used for routine thoracic CT without a significant loss of clinical scan quality. Thirty consecutive patients presenting for contrast thoracic CT were computer randomized into one of three groups: conventional, 1.0 pitch helical, and 1.5 pitch helical. All other variables, including kV, mA, slice thickness and reconstruction interval, and contrast administration, were kept constant. The studies were randomized to five independent, blinded, experienced radiologists who rated visualization 25 normal structures, and up to five pathologic findings per patient. In addition, each reader evaluated the studies' contrast enhancement, low contrast sensitivity, linear resolution, motion artifact, noise, and overall quality. The visualization score for all normal and overall for pathological lesions did not vary between groups. The three groups were not equivalent for several individual pathologic categories. However, these differences were not consistently in favor of one technique over the other two. The overall score for scan quality was not significantly different between the three groups. Extended 1.5 pitch thoracic helical CT provides equivalent quality versus either 1.0 pitch helical or conventional CT. The use of 1.5 pitch helical thoracic CT allows faster scanning, greater patient coverage, and the use of reduced amounts of intravenous contrast.

Diagnosis and differentiation of congenital diaphragmatic hernia from other noncardiac thoracic fetal masses.

This retrospective study was designed to evaluate individual sonographic parameters that might help differentiate congenital diaphragmatic hernia (CDH) from other noncardiac thoracic masses such as cystic adenomatoid malformation of the lung (CAML) and congenital lobar emphysema (CLE) prenatally. Twenty-four cases of CDH, CAML, and CLE detected during prenatal ultrasound and documented postnatally (with surgical, autopsy, or radiological proof) were identified through extensive chart and record review. The hard copy gray-scale images were retrospectively reviewed for imaging characteristics that may differentiate the three entities. Additionally, the prospective diagnosis during prenatal ultrasound was also compared with the postnatal diagnosis. The most reliable indicators in our retrospective review included confident visualization of a diaphragmatic defect (92.3/100.0 PPV/NPV, p< or =0.002) and/or localization of the stomach within the chest as well as the presence of severe cardiac deviation (both 92.3/62.5 PPV/NPV, p< or =0.01). Other sonographic indicators (including the presence of cystic areas, side and size of the lesion and the presence of polyhydramnios) offered lower levels of sensitivity and specificity. Prospective diagnosis during real-time assessment was also integral, offering >80% sensitivity and specificity (p< or =0.001). Accurate prenatal diagnosis of CDH is difficult despite the relative frequency of this lesion. The classic triad of a thoracic mass accompanying a displaced heart, absence of a normally positioned fluid-filled stomach and polyhydramnios, although seen with CDH, may not adequately differentiate this entity from other noncardiac fetal thoracic masses. Realtime assessment remains integral to the appropriate diagnosis.

Comparison of 1.0-, 1.5-, and 2.0-pitch abdominal helical computed tomography in evaluation of normal structures and pathologic lesions.

RATIONALE AND OBJECTIVES: The authors performed a comprehensive prospective clinical trial comparing 1.0-, 1.5-, and 2.0-pitch abdominal helical computed tomography (CT) in the evaluation of normal and pathologic structures/lesions. METHODS: Seventy-five consecutive patients were randomized by computer into one of three equal groups: helical CT pitch 1.0, 1.5, and 2.0. The imaging parameters and contrast enhancement of all 75 patients were kept constant. The 75 studies were masked, placed into a randomized order, and evaluated by five separate experienced radiologists who rated visualization of 25 normal structures and up to five pathologic findings per patient using a scale of 1 (not seen) to 5 (very well seen/very sharp margins). RESULTS: There were no statistical differences in 1.0- and 1.5-pitch abdominal CT scans when assessing the display of normal and pathologic lesions. In addition, helical pitch 1.0 and 1.5 studies were equivalent for both normal and pathologic structures/lesions, whereas equivalency was not demonstrated for helical pitch 2.0 studies. Overall study assessment questions again found equivalency between helical 1.0- and 1.5-pitch studies. CONCLUSIONS: Abdominal CT performed with pitches of 1.0 and 1.5 are equivalent. Because of its advantages, we advocate the routine use of an extended pitch (1.5) in routine abdominal CT. Further studies are required to evaluate the usefulness of the helical 2.0-pitch technique.

Thoracic spiral CT: delivery of contrast material pushed with injectable saline solution in a power injector.

A method of power injection of contrast material pushed with injectable saline solution during thoracic computed tomography (CT) was evaluated in 75 patients to help decrease the amount of contrast material necessary. Patients received 50-125 mL of 60% nonionic contrast material alone or pushed with 50 mL of saline. A volume of 75 mL of contrast material pushed with saline provided enhancement of the thoracic vasculature equal to that provided by a 125-mL volume of contrast material administered alone (P < .001) and caused significantly less beam-hardening artifact (P < .01).

The clinical usefulness of routine stacked multiplanar reconstruction in helical abdominal computed tomography.

RATIONALE AND OBJECTIVES: The authors evaluate the usefulness of stacked multiplanar reconstructions in routine, thick-section abdominal computed tomography. MATERIALS AND METHODS: Twenty-five routine, thick-section contrast abdominal CTs performed with equivalent technique were reformatted by multiplanar reconstructions in sagittal and coronal planes sequentially from side-to-side and front-to-back. The image sets were submitted, first axial images only followed by axial plus multiplanar reconstructions (MPRs), to 5 separate physician readers including 2 radiologists and 3 nonradiologists. These readers graded the visualization of a variety of normal and up to 5 pathologic lesions per patient on a scale of 1 to 5 (5 = best). RESULTS: The addition of sagittal and coronal multiplanar reconstructions significantly improved the visualization of all normal anatomic structures (mean axial only, 3.8; mean axial plus MPR, 4.1; P < 0.0001). In addition, most pathologic lesions were statistically better visualized with the addition of multiplanar reconstructions (mean axial images only, 3.9; mean axial plus MPR, 4.1; P < 0.0001). All five readers found improved visualization in nearly every category with the addition of the multiplanar reconstructions. However, in only 7% of cases, did a reviewer find new diagnostic information with the addition of MPR images. CONCLUSIONS: Stacked multiplanar reconstructions of routine, thick-section abdominal CT has clinical value in both the display of normal anatomic and pathologic lesions. Further studies, however, are required to confirm these findings before it is commonly used.

Technical factors of CT angiography studied with a carotid artery phantom.

PURPOSE: To evaluate scanning parameters (conventional versus spiral CT, section thickness, and pitch) and vessel orientation in the performance of CT angiography. METHODS: Conventional CT and 1.0-, 1.5-, and 2.0-pitch spiral CT acquisitions of a carotid phantom designed with vessels oriented parallel to the z-axis, 45 degrees oblique, and perpendicular to the z-axis were obtained with section thicknesses of 2, 4, and 8 mm. The phantom contained 32 vessels with 0% to 100% stenoses. Normal and stenotic luminal diameters were measured and the number of artifacts was assessed. RESULTS: No overall difference was observed among conventional and spiral CT acquisitions obtained with pitches of 1.0, 1.5, and 2.0. With thicker sections, CT angiographic accuracy decreased and artifacts increased. The three-vessel orientations were relatively comparable in accuracy in terms of the percentage of stenosis measured. Vessels parallel to the z-axis suffered less artifactual degradation. Unique artifacts, such as luminal distortion and beam hardening, were observed in vessels oriented at 45 degrees and perpendicular to the z-axis. CONCLUSION: Use of thinner sections with vessels oriented parallel to the z-axis optimizes CT angiographic quality. There is no apparent degradation with the use of spiral CT, and a pitch of 1.5 or 2.0 provides results equivalent to 1.0-pitch spiral studies.

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.

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.

The impact of 2D versus 3D quantitation of tumor bulk determination on current methods of assessing response to treatment.

PURPOSE: Measurements from sequential axial "2D" data in cancer patients are commonly used to assess treatment response or disease progression. This study compares the volume of tumor bulk calculated with 3D reconstructions with that calculated by conventional methods to determine if it might change patient classification. METHOD: All medical, gynecologic, and pediatric oncology patients under treatment who were evaluated with serial CT scans between January 1, 1992, and July 31, 1994, for whom the digital data were available were included in this study. For each tumor site, the maximum diameter and its perpendicular were measured and multiplied together to yield an area. The sum of areas of the measured lesions was used as an approximation of overall 2D tumor volume. In addition, the 2D area of each site was multiplied by its height, yielding a 2D volume. Last, the digital data were loaded into a 3D computer system and total 3D tumor volumes determined. All medical and gynecologic oncology patients were treated based upon the 2D area of tumor. The pediatric oncology patients were treated based upon the 2D volume of tumor measured as per standard practice. The members of each treating oncologic service assessed their patients as to how the other two methods would have changed their classification of the patients' response category. RESULTS: Four hundred thirty-three CT scans were performed in 139 patients, which included 204 baseline and 294 follow-up CT examinations. Seventy patients had new tumor foci and would have been classified as failure by all three methods of tumor bulk measurement. The 3D volume versus the 2D area method of tumor bulk assessment would have changed response categories in 52 of the 294 follow-up CT examinations (p < 0.0001). Thirty-five patients were recategorized from either "no response" to "failure" (21 patients) or "no response" to "response" (14 patients) categories. If only those follow-up studies without new metastatic foci are considered, the 3D volume versus the 2D area methods of tumor assessment would have changed the treatment response category in 23.2%. The use of the 2D volume method of calculating tumor volume of bulk tended to overestimate the overall tumor size by an average of 244 cm3 (p = 0.001). CONCLUSION: The 3D method of tumor volume measurement differs significantly from conventional 2D methods of tumor volume determination. Large prospective studies analyzing the usefulness of 3D tumor volume measurements and assessing possible changes in patient response categories would be required for full utilization of this more accurate method of following disease bulk.

Analysis of interobserver and intraobserver variability in CT tumor measurements.

OBJECTIVE: The purpose of this study was to evaluate the variability between radiologists interpreting thoracic and abdominal/pelvic CT scans in selecting specific sites of metastatic tumor for measurement (indicator lesions) and to assess interobserver and intraobserver variability in tumor measurement. MATERIALS AND METHODS: Three separate experienced radiologists were asked to review 24 combined thoracic and abdominal CT scans in patients with metastatic tumor. Each radiologist was asked to identify the indicator lesions representative of each patient's tumor bulk. In the second phase of the study, 105 specific foci on 26 combined thoracic and abdominal CT studies (including the original 24) were reviewed twice by the same three radiologists. Up to eight foci were randomly identified per patient, and each observer was asked to determine the slice with the maximum diameter for each tumor focus and to measure it in three dimensions (maximum diameter, its perpendicular, and length). RESULTS: A total of 132 tumor sites were present on the CT studies in phase I, all of which were chosen by at least one observer as an indicator lesion. Of the 116 of these that were separate and nonoverlapped, 57 (49%) were measured by only one observer, whereas 32 (28%) and 27 (23%) were measured by two or all three observers, respectively. Observers were more inclined to pick round or defined/well-defined lesions rather than irregular, oval, or poorly defined ones, although this tendency was not statistically significant. The second phase of the study showed considerable interobserver variability (15%) in CT tumor measurement, which was worse for poorly defined and irregular lesions. Intraobserver variability in measuring individual foci was less (6%). CONCLUSION: Radiologists interpreting thoracic and/or abdominal/pelvic CT scans for metastatic cancer should measure and report a significant number of each patient's tumor sites, especially larger ones in different anatomic areas. When interpreting a follow-up CT scan of a patient with metastatic cancer, the interpreting radiologist should remeasure the indicator lesions on the previous and on the follow-up CT scans, especially when the results will change the patient's treatment response category.

Routine use of a higher order interpolator and bone algorithm in thoracic CT.

OBJECTIVE: This study was designed to evaluate the utility of the routine use of high spatial frequency algorithms and higher order helical interpolators for imaging lung parenchyma during routine thoracic CT. SUBJECTS AND METHODS: We evaluated 50 consecutive patients undergoing clinically indicated thoracic CT using the same imaging parameters and scanner. The helical volume was reconstructed three separate times using standard and higher order (180 degrees linear with double-sided lobes) interpolators and standard and high spatial frequency (bone) algorithms. The images were photographed and given to five separate readers who were kept unaware of the interpolator and algorithm and who were asked to evaluate simultaneously each patient's three sets of images for best, in-between, and worst images of the lung interstitium, pathology, and normal anatomy. RESULTS: All five readers rated the standard interpolator and algorithm images as the worst (p < .01). All five readers consistently rated the double-sided lobe interpolator and bone algorithm images as the best (p < .01). CONCLUSION: A second reconstruction of routine thoracic helical CT data using higher order helical interpolators and a bone algorithm significantly improves interstitial detail of lung parenchyma and overall visualization of normal anatomy and pathologic processes.