Optimizing column-to-column retention time alignment in high-speed gas chromatography by combining retention time locking and correlation optimized warping.

We examine and then optimize alignment of chromatograms collected on nominally identical columns using retention time locking (RTL), an instrumental alignment tool, and software-based alignment using correlation optimized warping (COW). For this purpose, three samples are constructed by spiking two sets of analytes into a base test mixture. The three samples are analyzed by high-speed gas chromatography with four nominally identical columns and identical separation conditions. The data is first analyzed without alignment, then using COW alone, then RTL alone, and finally with RTL followed by COW to correct the severe column-to-column misalignment. Principal component analysis (PCA) is used to investigate how well each alignment method clustered the chromatograms into the three sample classes via a scores plot without being compromised by the specific column(s) used. The degree-of-class separation (DCS) is used as a classification metric, measured as the Euclidian distance between the centroids of two clusters in PC space in the scores plot, normalized by their pooled variance. With no alignment, the average DCS between sample classes (DCSsam) was 3.0, while the average DCS between the four nominally identical columns, i.e., column classes (DCScol) was 76.1 (ideally the DCScol should be 0), indicating the chromatograms were initially classified by the columns used. Using either COW or RTL alone also produced unsatisfactory results, with COW alone incorrectly aligning many peaks, leading to a DCSsam of only 1.9 and DCScol of 1.7, while RTL alone provided a DCSsam of 4.7 and DCScol of 4.2. Finally, using RTL followed by COW alignment, DCSsam increased to 32.5, indicating successful classification by chemical differences between sample classes, while the DCScol decreased to 0.4, indicating virtually no classification due to column-to-column differences, as desired. Thus, RTL provided a "first-order" correction of the initial retention mismatch observed for the nominally identical columns, while additional alignment via COW was required to optimize sample classification by PCA.

Comparison of MDCT protocols in trauma patients with suspected splenic injury: superior results with protocol that includes arterial and portal venous phase imaging.

PURPOSE: We aimed to determine which intravenous contrast-enhanced multidetector computed tomography (MDCT) protocol produced the most accurate results for the detection of splenic vascular injury in hemodynamically stable patients who had sustained blunt abdominal trauma. METHODS: We retrospectively reviewed 88 patients from 2003 to 2011 who sustained blunt splenic trauma and underwent contrast-enhanced MDCT and subsequent angiography. Results of MDCT scans utilizing single phase (portal venous only, n=8), dual phase (arterial + portal venous or portal venous + delayed, n=42), or triple phase (arterial + portal venous + delayed, n=38) were compared with results of subsequent splenic angiograms for the detection of splenic vascular injury. RESULTS: Dual phase imaging was more sensitive and accurate than single phase imaging (P = 0.016 and P = 0.029, respectively). When the subsets of dual phase imaging were compared, arterial + portal venous phase imaging was more sensitive and accurate than portal venous + delayed phase imaging (P = 0.005 and P = 0.002, respectively). Triple phase imaging was more accurate (P = 0.015) than dual phase; however, when compared with the dual phase subset of arterial + portal venous, there was no statistical difference in either sensitivity or accuracy. CONCLUSION: Our results support the use of dual phase contrast-enhanced MDCT, which includes the arterial phase, in patients with suspected splenic injury and question the utility of obtaining a delayed sequence.

Repeatability of 18F-FDG PET/CT in Advanced Non-Small Cell Lung Cancer: Prospective Assessment in 2 Multicenter Trials.

UNLABELLED: PET/CT with the glucose analog (18)F-FDG has several potential applications for monitoring tumor response to therapy in patients with non-small cell lung cancer (NSCLC). A prerequisite for many of these applications is detailed knowledge of the repeatability of quantitative parameters derived from (18)F-FDG PET/CT studies. METHODS: The repeatability of the (18)F-FDG signal was evaluated in 2 prospective multicenter trials. Patients with advanced NSCLC (tumor stage III-IV) underwent two (18)F-FDG PET/CT studies while not receiving therapy. Tumor (18)F-FDG uptake was quantified by measurement of the maximum standardized uptake value within a lesion (SUVmax) and the average SUV within a small volume of interest around the site of maximum uptake (SUVpeak). Analysis was performed for the lesion in the chest with the highest (18)F-FDG uptake and a size of at least 2 cm (target lesion) as well as for up to 6 additional lesions per patient. Repeatability was assessed by Bland-Altman plots and calculation of 95% repeatability coefficients (RCs) of the log-transformed SUV differences. RESULTS: Test-retest repeatability was assessed in 74 patients (34 from the ACRIN 6678 trial and 40 from the Merck MK-0646-008 trial). SUVpeak was 11.57 ± 7.89 g/mL for the ACRIN trial and 6.89 ± 3.02 for the Merck trial. The lower and upper RCs were -28% (95% confidence interval [CI], -35% to -23%) and +39% (95% CI, 31% to 54%) in the ACRIN trial, indicating that a decrease of SUVpeak by more than 28% or an increase by more than 39% has a probability of less than 2.5%. The corresponding RCs from the Merck trial were -35% (95% CI, -42% to -29%) and +53% (95% CI, 41% to 72%). Repeatability was similar for SUVmax of the target lesion, averaged SUVmax, and averaged SUVpeak of up to 6 lesions per patient. CONCLUSION: The variability of repeated measurements of tumor (18)F-FDG uptake in patients with NSCLC is somewhat larger than previously reported in smaller single-center studies but comparable to that of gastrointestinal malignancies in a previous multicenter trial. The variability of measurements supports the definitions of tumor response according to PET Response Criteria in Solid Tumors.

CT colonography for the detection of nonpolypoid adenomas: sensitivity assessed with restricted national CT colonography trial criteria.

OBJECTIVE: The purpose of this study was to determine the prevalence of nonpolypoid adenomas and the sensitivity of CT colonography (CTC) in their detection by use of the restricted criteria of height-to-width ratio<50% and height elevation≤3 mm. MATERIALS AND METHODS: In the National CT Colonography Trial (American College of Radiology Imaging Network protocol 6664), a cohort of 2531 participants without symptoms underwent CTC and screening colonoscopy. The CTC examinations were interpreted with both 2D and 3D techniques. Nonpolypoid adenomatous polyps identified with CTC or colonoscopy were retrospectively reviewed to determine which polyps met the restricted criteria. The prevalence of nonpolypoid adenomas and the prospective sensitivity of CTC were determined. Descriptive statistics were used to report the prevalence, size, and histologic features. The sensitivities (with 95% CIs) for nonpolypoid and polypoid lesions were compared by two-sided Z test for independent binomial proportions. RESULTS: The retrospective review confirmed 21 nonpolypoid adenomas, yielding a prevalence of 0.83% (21 of 2531 participants). Eight (38.1%) were advanced adenomas, many (50% [4/8]) only because of large size (≥10 mm). The overall per polyp sensitivity of CTC (combined 2D and 3D interpretation) for detecting nonpolypoid adenomas≥5 mm (n=21) was 0.76; ≥6 mm (n=16), 0.75; and ≥10 mm (n=5), 0.80. These values were not statistically different from the sensitivity of detecting polypoid adenomas (p>0.37). CONCLUSION: In this large screening population, nonpolypoid adenomas had a very low prevalence (<1%), and advanced pathologic features were uncommon in polyps<10 mm in diameter. Most nonpolypoid adenomas are technically visible at CTC. The prospective sensitivity is similar to that for polypoid adenomas when the interpretation combines both 2D and 3D review.

The National CT Colonography Trial: assessment of accuracy in participants 65 years of age and older.

PURPOSE: To conduct post-hoc analysis of National CT Colonography Trial data and compare the sensitivity and specificity of computed tomographic (CT) colonography in participants younger than 65 years with those in participants aged 65 years and older. MATERIALS AND METHODS: Of 2600 asymptomatic participants recruited at 15 centers for the trial, 497 were 65 years of age or older. Approval of this HIPAA-compliant study was obtained from the institutional review board of each site, and informed consent was obtained from each subject. Radiologists certified in CT colonography reported lesions 5 mm in diameter or larger. Screening detection of large (≥10-mm) histologically confirmed colorectal neoplasia was the primary end point; screening detection of smaller (6-9-mm) colorectal neoplasia was a secondary end point. The differences in sensitivity and specificity of CT colonography in the two age cohorts (age < 65 years and age ≥ 65 years) were estimated with bootstrap confidence intervals (CIs). RESULTS: Complete data were available for 477 participants 65 years of age or older (among 2531 evaluable participants). Prevalence of adenomas 1 cm or larger for the older participants versus the younger participants was 6.9% (33 of 477) versus 3.7% (76 of 2054) (P < .004). For large neoplasms, mean estimates for CT colonography sensitivity and specificity among the older cohort were 0.82 (95% CI: 0.644, 0.944) and 0.83 (95% CI: 0.779, 0.883), respectively. For large neoplasms in the younger group, CT colonography sensitivity and specificity were 0.92 (95% CI: 0.837, 0.967) and 0.86 (95% CI: 0.816, 0.899), respectively. Per-polyp sensitivity for large neoplasms for the older and younger populations was 0.75 (95% CI: 0.578, 0.869) and 0.84 (95% CI: 0.717, 0.924), respectively. For the older and younger groups, per-participant sensitivity was 0.72 (95% CI: 0.565, 0.854) and 0.81 (95% CI: 0.745, 0.882) for detecting adenomas 6 mm in diameter or larger. CONCLUSION: For most measures of diagnostic performance and in most subsets, the difference between senior-aged participants and those younger than 65 years was not statistically significant.

National CT colonography trial (ACRIN 6664): comparison of three full-laxative bowel preparations in more than 2500 average-risk patients.

OBJECTIVE: The purpose of our study was to compare the effect of three different full-laxative bowel preparations on patient compliance, residual stool and fluid, reader confidence, and polyp detection at CT colonography (CTC). SUBJECTS AND METHODS: A total of 2531 patients underwent CTC followed by colonoscopy for the American College of Radiology Imaging Network (ACRIN) National CTC Trial. Of this total, 2525 patients used one of three bowel preparations with bisacodyl tablets and stool and fluid tagging: 4 L of polyethylene glycol (PEG); 90 mL of phosphosoda; or 300 mL of magnesium citrate. Patients reported percent compliance with the bowel preparation and radiologists graded each CTC examination for the amount of residual fluid and stool on a scale from 1 (none) to 4 (nondiagnostic). Reader confidence for true-positive findings was reported on a 5-point scale: 1 (low) to 5 (high). Sensitivity and specificity for detecting polyps ≥ 6 mm and ≥ 1 cm compared with colonoscopy were calculated for each preparation. RESULTS: The most commonly prescribed preparation was phosphosoda (n = 1403) followed by PEG (n = 1020) and magnesium citrate (n = 102). Phosphosoda had the highest patient compliance (p = 0.01), least residual stool (p < 0.001), and highest reader confidence versus PEG for examinations with polyps (p = 0.06). Magnesium citrate had significantly more residual fluid compared with PEG and phosphosoda (p = 0.006). The sensitivity and specificity for detecting colon polyps ≥ 6 mm and ≥ 1 cm did not differ significantly between preparations. CONCLUSION: Polyp detection was comparable for all three preparations, although phosphosoda had significantly higher patient compliance and the least residual stool.

ACRIN CT colonography trial: does reader's preference for primary two-dimensional versus primary three-dimensional interpretation affect performance?

PURPOSE: To determine whether the reader's preference for a primary two-dimensional (2D) or three-dimensional (3D) computed tomographic (CT) colonographic interpretation method affects performance when using each technique. MATERIALS AND METHODS: In this institutional review board-approved, HIPAA-compliant study, images from 2531 CT colonographic examinations were interpreted by 15 trained radiologists by using colonoscopy as a reference standard. Through a survey at study start, study end, and 6-month intervals, readers were asked whether their interpretive preference in clinical practice was to perform a primary 2D, primary 3D, or both 2D and 3D interpretation. Readers were randomly assigned a primary interpretation method (2D or 3D) for each CT colonographic examination. Sensitivity and specificity of each method (primary 2D or 3D), for detecting polyps of 10 mm or larger and 6 mm or larger, based on interpretive preference were estimated by using resampling methods. RESULTS: Little change was observed in readers' preferences when comparing them at study start and study end, respectively, as follows: primary 2D (eight and seven readers), primary 3D (one and two readers), and both 2D and 3D (six and six readers). Sensitivity and specificity, respectively, for identifying examinations with polyps of 10 mm or larger for readers with a primary 2D preference (n = 1128 examinations) were 0.84 and 0.86, which was not significantly different from 0.84 and 0.83 for readers who preferred 2D and 3D (n = 1025 examinations) or from 0.76 and 0.82 for readers with a primary 3D preference (n = 378 examinations). When performance by using the assigned 2D or 3D method was evaluated on the basis of 2D or 3D preference, there was no difference among those readers by using their preferred versus not preferred method of interpretation. Similarly, no significant difference among readers or preferences was seen when performance was evaluated for detection of polyps of 6 mm or larger. CONCLUSION: The reader's preference for interpretive method had no effect on CT colonographic performance.

Blunt bowel and mesenteric injury: MDCT diagnosis.

Multidetector computed tomography (MDCT) has emerged as the imaging modality of choice for evaluating the abdomen and pelvis in trauma patients. MDCT readily detects injury of the solid organs as well as direct and indirect features of bowel and/or mesenteric injury-an important advance given that unrecognized bowel and mesenteric injuries may result in high morbidity and mortality. Nonetheless, challenges persist in the interpretation of abdominal and pelvic CT images in trauma patients. Difficulty in interpretation may result from lack of familiarity with or misunderstanding of CT features of bowel and/or mesenteric injury. Moreover, due to major technical advances afforded by MDCT, new CT features of bowel and/or mesenteric injuries have been recognized. Beading and termination of mesenteric vessels indicating surgically important mesenteric injury is an example of one of these new features. MDCT also allows for the detection of small or trace amounts of isolated intraperitoneal fluid in trauma patients, although the clinical management of these patients is still controversial. This pictorial essay illustrates the spectrum of typical, atypical, and newly reported MDCT features of bowel and mesenteric injuries due to blunt trauma. The features that help to differentiate these injuries from pitfalls are emphasized in these proven cases.

Frequency and importance of small amount of isolated pelvic free fluid detected with multidetector CT in male patients with blunt trauma.

PURPOSE: To retrospectively determine the frequency and importance of a small amount of isolated pelvic free fluid seen at multidetector computed tomography (CT) in male patients who have blunt trauma without an identifiable cause. MATERIALS AND METHODS: Institutional review board approval was obtained, and the requirement for informed consent was waived for this HIPAA-compliant study. One thousand male patients with blunt trauma who underwent abdominopelvic CT at a level 1 trauma center between January 2004 and June 2006 were entered into this study. The CT images of the 1000 patients were reviewed independently by two abdominal radiologists. CT scan assessment included evaluation for presence or absence of pelvic free fluid, any traumatic or nontraumatic cause of the free fluid, pelvic free fluid attenuation and volume measurements, and determination of the location of pelvic free fluid. Interobserver agreement was determined with kappa statistics, and the Student t test was used to assess differences in the mean volume and mean attenuation of the pelvic free fluid in the patients with and those without injury. RESULTS: Pelvic free fluid was identified in 10.2% (102 of 1000) of patients. A small amount of isolated pelvic free fluid without any identifiable cause was identified in 4.8% (48 of 1000) of patients by reader 1 and in 5.0% (50 of 1000) of patients by reader 2 (kappa value, 0.76) and was located at or below the level of the third sacral vertebral body in all 49 patients with isolated pelvic free fluid. The mean volume and mean attenuation of the small amount of isolated pelvic free fluid were 2.3 mL +/- 1.5 (standard deviation) and 8.1 HU +/- 3.9, respectively. None of the patients in this group had an undiagnosed bowel and/or mesenteric injury. CONCLUSION: In male patients with blunt trauma, a small amount of isolated pelvic free fluid with attenuation equal to that of simple fluid and located in the deep region of the pelvis likely is not a sign of bowel and/or mesenteric injury.

Can radiologist training and testing ensure high performance in CT colonography? Lessons From the National CT Colonography Trial.

OBJECTIVE: The objective of this article is to describe the experience of the National CT Colonography Trial with radiologist training and qualification testing at CT colonography (CTC) and to correlate this experience with subsequent performance in a prospective screening study. SUBJECTS AND METHODS: Ten inexperienced radiologists participated in a 1-day educational course, during which partial CTC examinations of 27 cases with neoplasia and full CTC examinations of 15 cases were reviewed using primary 2D and 3D search. Subsequently 15 radiologists took a qualification examination composed of 20 CTC cases. Radiologists who did not pass the first qualification examination attended a second day of focused retraining of 30 cases, which was followed by a second qualification examination. The results of the initial and subsequent qualification tests were compared with reader performance in a large prospective screening trial. RESULTS: All radiologists took and passed the qualification examinations. Seven radiologists passed the qualification examination the first time it was offered, and eight radiologists passed after focused retraining. Significantly better sensitivities were obtained on the second versus the first examination for the retrained radiologists (difference = 16%, p < 0.001). There was no significant difference in sensitivities between the groups who passed the qualification examination the first time versus those who passed the second time in the prospective study (88% vs 92%, respectively; p = 0.612). In the prospective study, the odds of correctly identifying diseased cases increased by 1.5 fold for every 50-case increase in reader experience or formal training (p < 0.025). CONCLUSION: A significant difference in performance was observed among radiologists before formalized training, but testing and focused retraining improved radiologist performance, resulting in an overall high sensitivity across radiologists in a subsequent, prospective screening study.

Accuracy of CT colonography for detection of large adenomas and cancers.

BACKGROUND: Computed tomographic (CT) colonography is a noninvasive option in screening for colorectal cancer. However, its accuracy as a screening tool in asymptomatic adults has not been well defined. METHODS: We recruited 2600 asymptomatic study participants, 50 years of age or older, at 15 study centers. CT colonographic images were acquired with the use of standard bowel preparation, stool and fluid tagging, mechanical insufflation, and multidetector-row CT scanners (with 16 or more rows). Radiologists trained in CT colonography reported all lesions measuring 5 mm or more in diameter. Optical colonoscopy and histologic review were performed according to established clinical protocols at each center and served as the reference standard. The primary end point was detection by CT colonography of histologically confirmed large adenomas and adenocarcinomas (10 mm in diameter or larger) that had been detected by colonoscopy; detection of smaller colorectal lesions (6 to 9 mm in diameter) was also evaluated. RESULTS: Complete data were available for 2531 participants (97%). For large adenomas and cancers, the mean (+/-SE) per-patient estimates of the sensitivity, specificity, positive and negative predictive values, and area under the receiver-operating-characteristic curve for CT colonography were 0.90+/-0.03, 0.86+/-0.02, 0.23+/-0.02, 0.99+/-<0.01, and 0.89+/-0.02, respectively. The sensitivity of 0.90 (i.e., 90%) indicates that CT colonography failed to detect a lesion measuring 10 mm or more in diameter in 10% of patients. The per-polyp sensitivity for large adenomas or cancers was 0.84+/-0.04. The per-patient sensitivity for detecting adenomas that were 6 mm or more in diameter was 0.78. CONCLUSIONS: In this study of asymptomatic adults, CT colonographic screening identified 90% of subjects with adenomas or cancers measuring 10 mm or more in diameter. These findings augment published data on the role of CT colonography in screening patients with an average risk of colorectal cancer. (ClinicalTrials.gov number, NCT00084929; American College of Radiology Imaging Network [ACRIN] number, 6664.)

CT colonography: false-negative interpretations.

PURPOSE: To retrospectively evaluate if false-negative interpretations at computed tomographic (CT) colonography are due to observer error. MATERIALS AND METHODS: This study was HIPAA compliant and had institutional review board approval, with waiver of informed consent. An initial unblinded review of CT colonographic image data was used to generate reconciliation reports for all false-negative polyp candidates 6.0 mm or larger. These findings were then verified by two experienced readers. After reports from the original study and reconciliation reports were reviewed, errors were classified as observer (measurement or perceptual) errors, technical errors (eg, those caused by insufficient distention, fluid), or not reconcilable. Per-polyp and per-patient sensitivity values were calculated for adenomas 6.0 mm or larger in the original data set and again by assuming elimination of technical and observer errors. RESULTS: Of the original data set of 228 available polyps, 147 were adenomas; for this subgroup, the per-patient sensitivity was 70% and 68% at 10.0- and 6.0-mm thresholds, respectively. When all histologic types were considered, 114 polyps were false-negative findings. Of these, 53% (60 of 114) were attributed to observer-related errors, and 26% were attributed to errors classified as technical. After detailed retrospective reconciliation of individual polyps (so as to exclude any potentially correctable observer error), the per-polyp sensitivity of CT colonography for adenomas 10.0 mm or larger increased to 93%, and the per-patient sensitivity increased to 91%. When observer and technical errors were accounted for, eight (5.4%) of 147 adenomas 6.0 mm or larger could not be detected. If all technical errors and observer errors were scored as true-positive findings, the sensitivity for adenomas 6.0 mm or larger would have been 95% on both a per-polyp and a per-patient basis. CONCLUSION: The major contributor to error at CT colonography was observer perceptual error, while observer measurement error played a smaller role.

Congenital anomalies and normal variants of the pancreaticobiliary tract and the pancreas in adults: part 1, Biliary tract.

OBJECTIVE: The purpose of this article is to highlight the imaging features of congenital anomalies and normal variants of the biliary tract with contemporary imaging techniques such as MR cholangiopancreatography (MRCP), MRI, and helical CT. CONCLUSION: Recognizing findings of congenital anomalies and normal variants of the biliary tract at MRCP, MRI, and helical CT, and knowledge of the clinical significance of each entity, are important for establishing a correct diagnosis and in guiding appropriate clinical management.

Congenital anomalies and normal variants of the pancreaticobiliary tract and the pancreas in adults: part 2, Pancreatic duct and pancreas.

OBJECTIVE: The purpose of this article is to highlight the imaging features of congenital anomalies and normal variants of the pancreatic duct and the pancreas using contemporary imaging techniques such as MR cholangiopancreatography (MRCP), MRI, and helical CT. CONCLUSION: Congenital anomalies and normal variants of the pancreatic duct and the pancreas may be clinically significant and may create a diagnostic challenge. Recognition of the updated imaging features of these entities is important in clinical management and for avoiding misdiagnosis.

Prospective comparison of patient experience with colon imaging tests.

PURPOSE: Patient experience varies with the currently available colon imaging tests, including air contrast barium enema, computed tomographic colonography, and colonoscopy. We examined differences in patient experience with colon imaging tests and whether they varied with gender, age, and race. SUBJECTS AND METHODS: Patients with fecal occult blood, hematochezia, iron-deficiency anemia, or a family history of colon cancer underwent air contrast barium enema followed 7 to 14 days later by computed tomographic colonography and colonoscopy. Validated patient experience questionnaires that measured the experience for each test and a separate questionnaire that obtained an overall summary measure were administered after testing. Eleven patient experiences including pain, embarrassment, difficulty with bowel preparation, and satisfaction with tests were examined. RESULTS: A total of 614 subjects completed all 3 imaging tests. The test most patients were willing to repeat was colonoscopy; it also was reported to be the least painful procedure. Patients were least satisfied with air contrast barium enema, and fewer would undergo air contrast barium enema compared with computed tomographic colonography or colonoscopy. There were limited racial and gender differences in perceptions of the tests. Younger adults perceived air contrast barium enema to be more painful than older adults. CONCLUSION: Taking into account a wide variety of patient experience measures, patients preferred colonoscopy to air contrast barium enema and computed tomographic colonography. This finding has important implications for physicians considering different colon imaging tests.

Helical CT evaluation of acute right lower quadrant pain: part I, common mimics of appendicitis.

OBJECTIVE: The purpose of our pictorial essay is to present common mimics of appendicitis as noted on helical CT in patients with right lower quadrant pain and to highlight the features that provide clues to the diagnosis. CONCLUSION: Recognition of the findings of common diseases that simulate acute appendicitis on helical CT, along with features that help to differentiate these entities from appendicitis, is important in establishing a correct diagnosis and in guiding appropriate therapy.

Helical CT evaluation of acute right lower quadrant pain: part II, uncommon mimics of appendicitis.

OBJECTIVE: The purpose of our pictorial essay is to highlight the helical CT features of uncommon mimics of appendicitis and to provide clues to differentiate them from appendicitis. CONCLUSION: Uncommon mimics of appendicitis create a diagnostic challenge in patients with right lower quadrant pain. Recognition of the helical CT features of uncommon mimics of appendicitis is important in clinical management and avoiding unnecessary laparotomy.