Amy K. Hara

Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study

OBJECTIVE The purpose of this study was to evaluate the image noise, low-contrast resolution, image quality, and spatial resolution of adaptive statistical iterative reconstruction in low-dose body CT. MATERIALS AND METHODS Adaptive statistical iterative reconstruction was used to scan the American College of Radiology phantom at the American College of Radiology reference value and at one-half that value (12.5 mGy). Test objects in low- and high-contrast and uniformity modules were evaluated. Low-dose CT with adaptive statistical iterative reconstruction was then tested on 12 patients (seven men, five women; average age, 67.5 years) who had previously undergone routine-dose CT. Two radiologists blinded to scanning technique evaluated images of the same patients obtained with routine-dose CT and low-dose CT with and without adaptive statistical iterative reconstruction. Image noise, low-contrast resolution, image quality, and spatial resolution were graded on a scale of 1 (best) to 4 (worst). Quantitative noise measurements were made on clinical images. RESULTS In the phantom, low- and high-contrast and uniformity assessments showed no significant difference between routine-dose imaging and low-dose CT with adaptive statistical iterative reconstruction. In patients, low-dose CT with adaptive statistical iterative reconstruction was associated with CT dose index reductions of 32-65% compared with routine imaging and had the least noise both quantitatively and qualitatively (p < 0.05). Low-dose CT with adaptive statistical iterative reconstruction and routine-dose CT had identical results for low-contrast resolution and nearly identical results for overall image quality (grade 2.1-2.2). Spatial resolution was better with routine-dose CT (p = 0.004). CONCLUSION These preliminary results support body CT dose index reductions of 32-65% when adaptive statistical iterative reconstruction is used. Studies with larger statistical samples are needed to confirm these findings.

A Meta-Analysis of the Yield of Capsule Endoscopy Compared to Other Diagnostic Modalities in Patients with Obscure Gastrointestinal Bleeding

OBJECTIVES:Due to its superior ability to examine the entire small bowel mucosa, capsule endoscopy (CE) has broadened the diagnostic evaluation of patients with obscure gastrointestinal bleeding (OGIB). Published studies have revealed a numerically superior performance of CE in determining a source of OGIB compared with other modalities, but due to small sample sizes, the overall magnitude of benefit is unknown. Additionally, the types of lesions more likely to be found by CE versus alternate modalities are also unknown. The aim of this study was to evaluate the yield of small bowel findings with CE in patients with OGIB compared to other modalities using meta-analysis.METHODS:We performed a recursive literature search of prospective studies comparing the yield of CE to other modalities in patients with OGIB. Data on yield and types of lesions identified among various modalities were extracted, pooled, and analyzed. Incremental yield (IY) (yield of CE–yield of comparative modality) and 95% confidence intervals (95% CI) of CE over comparative modalities were calculated.RESULTS:A total of 14 studies (n = 396) compared the yield of CE with push enteroscopy for OGIB. The yield for CE and push enteroscopy was 63% and 28%, respectively (IY = 35%, p < 0.00001, 95% CI = 26–43%) and for clinically significant findings (n = 376) was 56% and 26%, respectively (IY = 30%, p < 0.00001, 95% CI = 21–38%). Three studies (n = 88) compared the yield of CE to small bowel barium radiography. The yield for CE and small bowel barium radiography for any finding was 67% and 8%, respectively (IY = 59%, p < 0.00001, 95% CI = 48–70%) and for clinically significant findings was 42% and 6%, respectively (IY = 36%, p < 0.00001, 95% CI = 25–48%). Number needed to test (NNT) to yield one additional clinically significant finding with CE over either modality was 3 (95% CI = 2–4). One study each compared the yield of significant findings on CE to intraoperative enteroscopy (n = 42, IY = 0%, p = 1.0, 95% CI =−16% to 16%), computed tomography enteroclysis (n = 8, IY = 38%, p = 0.08, 95% CI =−4% to 79%), mesenteric angiogram (n = 17, IY =−6%, p = 0.73, 95% CI =−39% to 28%), and small bowel magnetic resonance imaging (n = 14, IY = 36%, p = 0.007, 95% CI = 10–62%). Ten of the 14 trials comparing CE with push enteroscopy classified the types of lesions found on examination. CE had a 36% yield for vascular lesions versus 20% for push enteroscopy, with an IY of 16% (p < 0.00001, 95% CI = 9–23%). Inflammatory lesions were also found more often in CE (11%) than in push enteroscopy (2%), with an IY of 9% (p = 0.0001, 95% CI = 5–13%). There was no significant difference in the yield of tumors or “other” findings between CE and push enteroscopy.CONCLUSIONS:CE is superior to push enteroscopy and small bowel barium radiography for diagnosing clinically significant small bowel pathology in patients with OGIB. In study populations, the IY of CE over push enteroscopy and small bowel barium radiography for clinically significant findings is ≥30% with an NNT of 3, primarily due to visualization of additional vascular and inflammatory lesions by CE.

Innovations in CT Dose Reduction Strategy: Application of the Adaptive Statistical Iterative Reconstruction Algorithm

OBJECTIVE The purpose of this article is to discuss the application of a new CT reconstruction algorithm, adaptive statistical iterative reconstruction (ASIR), to reduce radiation dose at body CT and to provide imaging examples in comparison with low-dose and standard-dose filtered back projection CT. CONCLUSION The ASIR reconstruction algorithm is a promising technique for providing diagnostic quality CT images at significantly reduced radiation doses.

A Meta-Analysis of the Yield of Capsule Endoscopy Compared to Other Diagnostic Modalities in Patients with Non-Stricturing Small Bowel Crohn's Disease

OBJECTIVES:Capsule endoscopy (CE) allows for direct evaluation of the small bowel mucosa in patients with Crohns disease (CD). A number of studies have revealed significantly improved yield for CE over other modalities for the diagnosis of CD, but as sample sizes have been small, the true degree of benefit is uncertain. Additionally, it is not clear whether patients with a suspected initial presentation of CD and those with suspected recurrent disease are equally likely to benefit from CE. The aim of this study was to evaluate the yield of CE compared with other modalities in symptomatic patients with suspected or established CD using meta-analysis.METHODS:We performed a recursive literature search of prospective studies comparing the yield of CE to other modalities in patients with suspected or established CD. Data on yield among various modalities were extracted, pooled, and analyzed. Incremental yield (IY) (yield of CE − yield of comparative modality) and 95% confidence intervals (95% CI) of CE over comparative modalities were calculated. Subanalyses of patients with a suspected initial presentation of CD and those with suspected recurrent disease were also performed.RESULTS:Nine studies (n = 250) compared the yield of CE with small bowel barium radiography for the diagnosis of CD. The yield for CE versus barium radiography for all patients was 63% and 23%, respectively (IY = 40%, p < 0.001, 95% CI = 28–51%). Four trials compared the yield of CE to colonoscopy with ileoscopy (n = 114). The yield for CE versus ileoscopy for all patients was 61% and 46%, respectively (IY = 15%, p= 0.02, 95% CI = 2–27%). Three studies compared the yield of CE to computed tomography (CT) enterography/CT enteroclysis (n = 93). The yield for CE versus CT for all patients was 69% and 30%, respectively (IY = 38%, p= 0.001, 95% CI = 15–60%). Two trials compared CE to push enteroscopy (IY = 38%, p < 0.001, 95% CI = 26–50%) and one trial compared CE to small bowel magnetic resonance imaging (MRI) (IY = 22%, p= 0.16, 95% CI =−9% to 53%). Subanalysis of patients with a suspected initial presentation of CD showed no statistically significant difference between the yield of CE and barium radiography (p= 0.09), colonoscopy with ileoscopy (p= 0.48), CT enterography (p= 0.07), or push enteroscopy (p= 0.51). Subanalysis of patients with established CD with suspected small bowel recurrence revealed a statistically significant difference in yield in favor of CE compared with all other modalities (barium radiography (p < 0.001), colonoscopy with ileoscopy (p= 0.002), CT enterography (p < 0.001), and push enteroscopy (p < 0.001)).CONCLUSIONS:In study populations, CE is superior to all other modalities for diagnosing non-stricturing small bowel CD, with a number needed to test (NNT) of 3 to yield one additional diagnosis of CD over small bowel barium radiography and NNT = 7 over colonoscopy with ileoscopy. These results are due to a highly significant IY with CE over all other modalities in patients with established non-stricturing CD being evaluated for a small bowel recurrence. While there was no significant difference seen between CE and alternate modalities for diagnosing small bowel CD in patients with a suspected initial presentation of CD, the trend toward significance for a number of modalities suggests the possibility of a type II error. Larger studies are needed to better establish the role of CE for diagnosing small bowel CD in patients with a suspected initial presentation of CD.

Abdominal CT: Comparison of Low-Dose CT With Adaptive Statistical Iterative Reconstruction and Routine-Dose CT With Filtered Back Projection in 53 Patients

OBJECTIVE The purpose of this article is to retrospectively compare radiation dose, noise, and image quality of abdominal low-dose CT reconstructed with adaptive statistical iterative reconstruction (ASIR) and routine-dose CT reconstructed with filtered back projection (FBP). MATERIALS AND METHODS Fifty-three patients (37 men and 16 women; mean age, 60.8 years) underwent contrast-enhanced abdominal low-dose CT with 40% ASIR. All 53 patients had previously undergone contrast-enhanced routine-dose CT with FBP. With the scanning techniques masked, two radiologists independently graded images for sharpness, image noise, diagnostic acceptability, and artifacts. Quantitative measures of radiation dose and image noise were also obtained. All results were compared on the basis of body mass index (BMI). RESULTS The volume CT dose index (CTDI(vol)), dose-length product, and radiation dose for low-dose CT with ASIR were 17 mGy, 860 mGy, and 13 mSv, respectively, compared with 25 mGy, 1,193 mGy, and 18 mSv for routine-dose CT with FBP, representing an approximate overall dose reduction of 33%. Low-dose CT with ASIR had significantly reduced (p < 0.001) quantitative and qualitative assessment of image noise. Image sharpness, however, was significantly reduced for low-dose CT with ASIR (p < 0.001), although diagnostic acceptability and artifact scores were nearly identical to those for routine-dose CT with FBP. The average CTDI(vol) dose reduction was 66% for patients with a BMI of less than 20 and 23% for patients with a BMI of 25 or greater. CONCLUSION Compared with routine-dose CT with FBP, abdominal low-dose CT with ASIR significantly reduces noise, thereby permitting diagnostic abdominal examinations with lower (by 23-66%) radiation doses. Despite reduced image sharpness in average and small patients, low-dose CT with ASIR had diagnostic acceptability comparable to that of routine-dose CT with FBP.

Capsule endoscopy has a significantly higher diagnostic yield in patients with suspected and established small-bowel Crohn's disease: a meta-analysis

OBJECTIVES:Capsule endoscopy (CE) has demonstrated superior performance compared with other modalities in its ability to detect early small-bowel (SB) Crohns disease (CD), especially when ileoscopy is negative or unsuccessful. The aim of this study was to evaluate the diagnostic yield of CE compared with other modalities in patients with suspected and established CD using a meta-analysis.METHODS:A thorough literature search for prospective studies comparing the diagnostic yield of CE with other modalities in patients with CD was undertaken. Other modalities included push enteroscopy (PE), colonoscopy with ileoscopy (C+IL), SB radiography (SBR), computed tomography enterography (CTE), and magnetic resonance enterography (MRE). Data on diagnostic yield among various modalities were extracted, pooled, and analyzed. Data on patients with suspected and established CD were analyzed separately. Weighted incremental yield (IYW) (diagnostic yield of CE−diagnostic yield of comparative modality) and 95% confidence intervals (CIs) of CE over comparative modalities were calculated.RESULTS:A total of 12 trials (n=428) compared the yield of CE with SBR in patients with CD. Eight trials (n=236) compared CE with C+IL, four trials (n=119) compared CE with CTE, two trials (n=102) compared CE with PE, and four trials (n=123) compared CE with MRE. For the suspected CD subgroup, several comparisons met statistical significance. Yields in this subgroup were CE vs. SBR: 52 vs. 16% (IYw=32%, P<0.0001, 95% CI=16–48%), CE vs. CTE: 68 vs. 21% (IYw=47%, P<0.00001, 95% CI=31–63%), and CE vs. C+IL: 47 vs. 25% (IYw=22%, P=0.009, 95% CI=5–39%). Statistically significant yields for CE vs. an alternate diagnostic modality in established CD patients were seen in CE vs. PE: 66 vs. 9% (IYw=57%, P<0.00001, 95% CI=43–71%), CE vs. SBR: 71 vs. 36% (IYw=38%, P<0.00001, 95% CI=22–54%), and in CE vs. CTE: 71 vs. 39% (IYw=32%, P=<0.0001, 95% CI=16–47%).CONCLUSIONS:Our meta-analysis demonstrates that CE is superior to SBR, CTE, and C+IL in the evaluation of suspected CD patients. CE is also a more effective diagnostic tool in established CD patients compared with SBR, CTE, and PE.

Dual-Energy (Spectral) CT: Applications in Abdominal Imaging

Dual-energy imaging is a promising new development in computed tomography (CT) that has the potential to improve lesion detection and characterization beyond levels currently achievable with conventional CT techniques. In dual-energy CT (DECT), the simultaneous use of two different energy settings allows the differentiation of materials on the basis of their energy-related attenuation characteristics (material density). The datasets obtained with DECT can be used to reconstruct virtual unenhanced images as well as iodinated contrast material-enhanced material density images, obviating the standard two-phase (unenhanced and contrast-enhanced) scanning protocol and thus helping minimize the radiation dose received by the patient. Single-source DECT, which is performed with rapid alternation between two energy levels, can also generate computed monochromatic images, which are less vulnerable to artifacts such as beam hardening and pseudoenhancement and provide a higher contrast-to-noise ratio than polychromatic images produced by conventional CT. Familiarity with the capabilities of DECT may help radiologists improve their diagnostic performance.

Reducing the Radiation Dose for CT Colonography Using Adaptive Statistical Iterative Reconstruction: A Pilot Study

OBJECTIVE The purpose of our study was to evaluate the feasibility of preserving image quality during CT colonography (CTC) using a reduced radiation dose with adaptive statistical iterative reconstruction (ASIR). MATERIALS AND METHODS A proven colon phantom was imaged at standard dose settings (50 mAs) and at reduced doses (10-40 mAs) using six different ASIR levels (0-100%). We assessed 2D and 3D image quality and noise to determine the optimal dose and ASIR setting. Eighteen patients were then scanned with a standard CTC dose (50 mAs) in the supine position and at a reduced dose of 25 mAs with 40% ASIR in the prone position. Three radiologists blinded to the scanning techniques assessed 2D and 3D image quality and noise at three different colon locations. A score difference of > or = 1 was considered clinically important. Actual noise measures were compared between the standard-dose and low-dose acquisitions. RESULTS The phantom study showed image noise reduction that correlated with a higher percentage of ASIR. In patients, no significant image quality differences were identified between standard- and low-dose images using 40% ASIR. Overall image quality was reduced for both image sets as body mass index increased. Measured image noise was less with the low-dose technique using ASIR. CONCLUSION The results of this pilot study show that the radiation dose during CTC can be reduced 50% below currently accepted low-dose techniques without significantly affecting image quality when ASIR is used. Further evaluation in a larger patient group is warranted.

Detection of flat lesions in the colon with CT colonography

AbstractBackground:We investigated whether flat lesions of the colon could be detected on computed tomographic colonography (CTC). Methods: CTC and conventional colonoscopy were performed on 547 consecutive patients. A subset of 22 polyps was described as flat on colonoscopy (n= 16) or CTC (n= 6) and are the basis of this report. CTC was performed with a standard technique (5-mm collimation, 3-mm reconstruction intervals). Patients were scanned in supine and prone positions. Examinations were randomly assigned and reviewed in a blinded fashion by two of three radiologists. Prospective interpretations were recorded. All patients had conventional colonoscopy, which served as the gold standard. Results: Twenty-two flat lesions ranging from 0.4 to 3.5 cm were histologically classified as adenomatous (n= 8) or hyperplastic (n= 14). The sensitivities for detecting all flat lesions and flat adenomas by each reviewer were 43% and 100%, 65% and 100%, and 15% and 13%, respectively. “Double reading” resulted in detection of 68% of all lesions and 100% of adenomas. Of the seven hyperplastic polyps missed by both reviewers, four were identified retrospectively. Conclusion: Flat lesions of the colon represent an important source of false negative CTC examinations. Awareness of their morphology can assist radiologists in finding most of these challenging lesions.

Computerized tomographic colonography: Performance evaluation in a retrospective multicenter setting

BACKGROUND & AIMS No multicenter study has been reported evaluating the performance and interobserver variability of computerized tomographic colonography. The aim of this study was to assess the accuracy of computerized tomographic colonography for detecting clinically important colorectal neoplasia (polyps >or=10 mm in diameter) in a multi-institutional study. METHODS A retrospective study was developed from 341 patients who had computerized tomographic colonography and colonoscopy among 8 medical centers. Colonoscopy and pathology reports provided the standard. A random sample of 117 patients, stratified by criterion standard, was requested. Ninety-three patients were included (47% with polyps >or=10 mm; mean age, 62 years; 56% men; 84% white; 40% reported colorectal symptoms; 74% at increased risk for colorectal cancer). Eighteen radiologists blinded to the criterion standard interpreted computerized tomography colonography examinations, each using 2 of 3 different software display platforms. RESULTS The average area under the receiver operating characteristic curve for identifying patients with at least 1 lesion >or=10 mm was 0.80 (95% lower confidence bound, 0.74). The average sensitivity and specificity were 75% (95% lower confidence bound, 68%) and 73% (95% lower confidence bound, 66%), respectively. Per-polyp sensitivity was 75%. A trend was observed for better performance with more observer experience. There was no difference in performance across software display platforms. CONCLUSIONS Computerized tomographic colonography performance compared favorably with reported performance of fecal occult blood testing, flexible sigmoidoscopy, and barium enema. A prospective study evaluating the performance of computerized tomography colonography in a screening population is indicated.