Jackknife Alternative Free-response Receiver Operating Characteristic Research Articles

Diagnostic performance of reduced-dose CT with a hybrid iterative reconstruction algorithm for the detection of hypervascular liver lesions: a phantom study.

To investigate the diagnostic performance of reduced-dose CT with a hybrid iterative reconstruction (IR) algorithm for the detection of hypervascular liver lesions. Thirty liver phantoms with or without simulated hypervascular lesions were scanned with a 320-slice CT scanner with control-dose (40 mAs) and reduced-dose (30 and 20 mAs) settings. Control-dose images were reconstructed with filtered back projection (FBP), and reduced-dose images were reconstructed with FBP and a hybrid IR algorithm. Objective image noise and the lesion to liver contrast-to-noise ratio (CNR) were evaluated quantitatively. Images were interpreted independently by 2 blinded radiologists, and jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis was performed. Hybrid IR images with reduced-dose settings (both 30 and 20 mAs) yielded significantly lower objective image noise and higher CNR than control-dose FBP images (P < .05). However, hybrid IR images with reduced-dose settings had lower JAFROC1 figure of merit than control-dose FBP images, although only the difference between 20 mAs images and control-dose FBP images was significant for both readers (P < .01). An aggressive reduction of the radiation dose would impair the detectability of hypervascular liver lesions, although objective image noise and CNR would be preserved by a hybrid IR algorithm. • A half-dose scan with a hybrid iterative reconstruction preserves objective image quality. • A hybrid iterative reconstruction algorithm does not improve diagnostic performance. • An aggressive dose reduction would impair the detectability of low-contrast lesions.

One-mSv CT colonography: Effect of different iterative reconstruction algorithms on radiologists’ performance

PurposeTo analyze the effect of different reconstruction algorithms on image noise and radiologists’ performance at ultra-low dose CT colonography (CTC) in human subjects. Materials and methodsThis retrospective study had institutional review board approval, with waiver of the need to obtain informed consent. CTC and subsequent colonoscopy were performed at the same day in 28 patients. CTC was scanned at the supine/prone positions using 120/100kVp and fixed 10mAs, and reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based IR (Veo) algorithms. Size-specific dose estimates (SSDE) and effective radiation doses were recorded. Image noise was compared among the three datasets using repeated measures analysis of variance (ANOVA). Per-polyp sensitivity and figure-of-merits were compared among the datasets using the McNemar test and jackknife alternative free-response receiver operating characteristic (JAFROC) analysis, respectively, by one novice and one expert reviewer in CTC. ResultsMean SSDE and effective radiation dose of CTC were 1.732mGy and 1.002mSv, respectively. Mean image noise at supine/prone position datasets was significantly lowest with Veo (17.2/13.3), followed by ASIR (52.4/38.9) and FBP (69.9/50.8) (P<0.0001). Forty-two polyps in 25 patients were reference polyps. For both readers, per-polyp sensitivity of all 42 polyps was highest with Veo reconstruction (81.0%, 64.3%), followed by ASIR (73.8%, 54.8%) and FBP (57.1%, 50.0%) with statistical significance between Veo and FBP for reader 1 (P=0.002). JAFROC analysis revealed that the figure-of-merit for the detection of polyps was highest with Veo (0.917, 0.786), followed by ASIR (0.881, 0.750) and FBP (0.750, 0.746) with statistical significances between Veo or ASIR and FBP for reader 1 (P<0.05). ConclusionOne-mSv CTC was not feasible using the standard FBP algorithm. However, diagnostic performance expressed as per-polyp sensitivity and figures-of-merit can be improved with the application of IR algorithms, particularly Veo.

Addition of Digital Breast Tomosynthesis to Full-Field Digital Mammography in the Diagnostic Setting: Additional Value and Cancer Detectability.

PurposeThe purpose of this study was to assess the value of adding digital breast tomosynthesis (DBT) to full-field digital mammography (FFDM) in the diagnostic workup of breast cancer and to determine which lesion variables affect cancer detectability in the combined modality.MethodsBetween March and May 2012, paired FFDM and DBT images were obtained from 203 women as part of a diagnostic workup for breast cancer. Images from FFDM alone, DBT alone, and DBT combined with FFDM were reviewed in separate sessions by six blinded readers. Jackknife alternative free-response receiver operating characteristic (JAFROC) figure of merit (FOM), sensitivity, and specificity were compared between the modalities. Lesion characteristics affecting the cancer detection rate when using the combined modality were also analyzed.ResultsAmong the 203 women, 126 women had a total of 129 malignancies and 77 women had total of 77 benign lesions. The overall JAFROC FOM of the combined modality was higher than that of FFDM alone (0.827 vs. 0.775, p<0.001) and that of DBT alone was higher than that of FFDM alone (0.807 vs. 0.775, p=0.027). The overall sensitivity of the combined modality was higher than that of FFDM alone (80.0% vs. 73.2%, p<0.001) and that of DBT alone was higher than that of FFDM alone (78.3% vs. 73.2%, p=0.007). Compared to FFDM alone, the combined modality detected an additional 48 cancers. Using the combined modality, the presence of masses or microcalcifications was significantly associated with the cancer detection rate (p<0.001).ConclusionThe combination of DBT with FFDM results in a higher diagnostic yield than FFDM alone. Additionally, DBT alone performs better than FFDM alone. However, even when DBT is combined with FFDM, breast cancers with no discernible masses and those lacking calcifications are difficult to detect.

Navigated three-dimensional T1-weighted gradient-echo sequence for gadoxetic acid liver magnetic resonance imaging in patients with limited breath-holding capacity.

To determine whether a navigator-gated three-dimensional T1-weighted gradient-echo sequence (T1W-GRE, navigated LAVA) can improve diagnostic performance for the detection of focal liver lesions (FLLs) compared to standard breath-hold (BH) T1W-GRE breath-hold LAVA (BH-LAVA) during the hepatobiliary phase (HBP) of gadoxetic acid liver magnetic resonance imaging (MRI) in patients with limited breath-holding capacity. This retrospective study was approved by our institutional review board and the requirement for informed consent was waived. We included 372 patients who underwent liver MRI including both navigated LAVA and BH-LAVA sequences. Overall image quality of the two HBP image sets was compared. In patients with limited breath-holding capacity, diagnostic performances in detecting FLLs on the two HBP images were compared using jackknife-alternative free-response receiver-operating characteristic (JAFROC) analysis by two reviewers. There were 13 cases (13/372; 3.5%) of image acquisition failure using the navigated LAVA sequence due to severe irregular breathing, and 50 of 359 patients had limited breath-holding capacity. In these patients, overall image quality of navigated LAVA (2.78±0.95) was significantly better than that of BH-LAVA (2.42±0.81, P<0.005), and both readers showed significantly higher JAFROC figure-of-merit values with navigated LAVA compared to BH-LAVA (0.94 and 0.86 in reviewer 1, respectively; 0.89 and 0.83 in reviewer 2, respectively, P<0.005). Overall image quality of navigated LAVA was also better than that of BH-LAVA in patients with sufficient breath-holding capacity (n=309, 3.96±0.88, 3.81±0.66, respectively, P<0.001). The navigated LAVA sequence could provide better image quality and diagnostic performance in detecting FLLs than BH-LAVA in patients with limited breath-holding capacity during HBP of gadoxetic acid MRI.

The effect of image processing on the detection of cancers in digital mammography.

OBJECTIVE. The objective of our study was to investigate the effect of image processing on the detection of cancers in digital mammography images. MATERIALS AND METHODS. Two hundred seventy pairs of breast images (both breasts, one view) were collected from eight systems using Hologic amorphous selenium detectors: 80 image pairs showed breasts containing subtle malignant masses; 30 image pairs, biopsy-proven benign lesions; 80 image pairs, simulated calcification clusters; and 80 image pairs, no cancer (normal). The 270 image pairs were processed with three types of image processing: standard (full enhancement), low contrast (intermediate enhancement), and pseudo-film-screen (no enhancement). Seven experienced observers inspected the images, locating and rating regions they suspected to be cancer for likelihood of malignancy. The results were analyzed using a jackknife-alternative free-response receiver operating characteristic (JAFROC) analysis. RESULTS. The detection of calcification clusters was significantly affected by the type of image processing: The JAFROC figure of merit (FOM) decreased from 0.65 with standard image processing to 0.63 with low-contrast image processing (p = 0.04) and from 0.65 with standard image processing to 0.61 with film-screen image processing (p = 0.0005). The detection of noncalcification cancers was not significantly different among the image-processing types investigated (p > 0.40). CONCLUSION. These results suggest that image processing has a significant impact on the detection of calcification clusters in digital mammography. For the three image-processing versions and the system investigated, standard image processing was optimal for the detection of calcification clusters. The effect on cancer detection should be considered when selecting the type of image processing in the future.

Re-evaluation of detectability of liver metastases by contrast-enhanced CT: added value of hepatic arterial phase imaging.

We compared the detectability of liver metastases on 2- and 3-phase images using robust statistical methods. Nine radiologists evaluated unenhanced CT plus portal venous phase (2-phase) images and 2-phase plus hepatic arterial phase (HAP) (3-phase) images. Our study included 54 patients with primary malignant tumors who underwent 3-phase hepatic dynamic CT more than twice to screen for liver metastases; 24 had 1-6 liver metastases measuring 4-27 mm in diameter (median 13 mm). The other 30 had no metastases. Nine board-certified radiologists participated in our observer performance study. They specified the location of the metastatic lesions and rated the probability of metastatic nodules on 2-phase images acquired with and without HAP imaging. We used jackknife alternative free-response receiver operating characteristic (JAFROC) analysis to compare their performances. For all radiologists the area under the curve without and with HAP imaging was 0.86 and 0.88, respectively; the difference was significant (p = 0.04). For metastases smaller than 10 mm the averaged lesion localization fraction without and with HAP imaging was 0.17 and 0.26 (p < 0.01). Adding HAP to 2-phase imaging improved the detectability of liver metastases, especially of lesions smaller than 10 mm.

A Free-response Evaluation Determining Value in the Computed Tomography Attenuation Correction Image for Revealing Pulmonary Incidental Findings: A Phantom Study

The purpose of this study was to compare lesion-detection performance when interpreting computed tomography (CT) images that are acquired for attenuation correction when performing single photon emission computed tomography/computed tomography (SPECT/CT) myocardial perfusion studies. In the United Kingdom, there is a requirement that these images be interpreted; thus, it is necessary to understand observer performance on these images.An anthropomorphic chest phantom with inserted spherical lesions of different sizes and contrasts was scanned on five different SPECT/CT systems using site-specific CT protocols for SPECT/CT myocardial perfusion imaging. Twenty-one observers (0-4 years of CT experience) searched 26 image slices (17 abnormal, containing 1-3 lesions, and 9 normal, containing no lesions) for each CT acquisition. The observers marked and rated perceived lesions under the free-response paradigm. Four analyses were conducted using jackknife alternative free-response receiver operating characteristic (JAFROC) analysis: (1) 20-pixel acceptance radius (AR) with all 21 readers, abbreviated to 20/ALL analysis, (2) 40-pixel AR with 21 readers (40/ALL), (3) 20-pixel AR with 14 readers experienced in CT (20/EXP), and (4) 20-pixel AR with 7 readers with no CT experience (20/NOT). The significance level of the test was set so as to conservatively control the overall probability of a type I error to <0.05.The mean JAFROC figure of merit (FOM) for the five CT acquisitions for the 20/ALL study were 0.602, 0.639, 0.372, 0.475, and 0.719 with a significant difference in lesion-detection performance evident between all individual treatment pairs (P < .0001) with the exception of the 1-2 pairing, which was not significant (these differed only in milliamp seconds). System 5, which had the highest performance, had the smallest slice thickness and the largest matrix size. For the other analyses, the system orderings remained unchanged, and the significance of FOM difference findings remained identical to those for 20/ALL, with one exception: for 20/EXP analysis the 1-2 difference became significant with the higher milliamp seconds superior. Improved detection performance was associated with a smaller slice thickness, increased matrix size, and, to a lesser extent, increased tube charge.Protocol variations for CT-based attenuation correction (AC) in SPECT/CT imaging have a measurable impact on lesion-detection performance. The results imply that z-axis resolution and matrix size had the greatest impact on lesion detection, with a weaker but detectable dependence on the product of milliamp and seconds.

Small (≤1-cm) Hepatocellular Carcinoma: Diagnostic Performance and Imaging Features at Gadoxetic Acid–enhanced MR Imaging

To assess diagnostic performance and imaging features of gadoxetic acid-enhanced magnetic resonance (MR) imaging in small (≤1-cm) hepatocellular carcinoma (HCC) detection in patients with chronic liver disease. The institutional review board approved this retrospective study and waived informed consent. Sixty patients (56 men, four women; mean age, 60.1 years) with HCC (146 lesions; 70 > 1 cm, 76 ≤ 1 cm) underwent gadoxetic acid-enhanced MR imaging. HCC was confirmed at surgical resection (72 lesions; 30 > 1 cm, 42 ≤ 1 cm) or by showing interval growth with typical enhancement patterns at follow-up dynamic computed tomography or MR imaging (74 lesions; 40 > 1 cm, 34 ≤ 1 cm). Two radiologists assessed MR imaging features and graded likelihood of HCC with a five-point confidence scale. Jackknife alternative free-response receiver operating characteristic (JAFROC) method was used. Mean JAFROC figure of merit for small HCC was 0.717; that for large (>1-cm) HCC was 0.973 with substantial agreement (κ = 0.676). Mean sensitivity and positive predictive value (PPV) were 46.0% (70 of 152) and 48.3% (70 of 145) for small HCC versus 95.0% (133 of 140) and 78.2% (133 of 170) for large HCC, respectively. Eleven of 76 small HCCs (14%) were not seen on MR images, even after careful investigation. MR imaging features of small HCC included arterial enhancement (79%, 60 of 76), hypointensity on hepatobiliary phase (HBP) images (68%, 52 of 76), washout on 3-minute delayed phase images (50%, 38 of 76), hyperintensity on T2-weighted images (43%, 33 of 76), hypointensity on T1-weighted images (32%, 24 of 76), and restriction on diffusion-weighted images (28%, 20 of 72). Arterial enhancement and washout on 3-minute delayed phase images or hypointensity on HBP images occurred in 66% of small HCCs (50 of 76). Diagnostic performance of gadoxetic acid-enhanced MR imaging for small HCC detection is still low, with mean sensitivity of 46.0% (70 of 152) and mean PPV of 48.3% (70 of 145). By adding hypointensity on HBP images as washout, diagnostic performance for small HCC detection can be improved.

Computer-aided detection of clustered microcalcifications in multiscale bilateral filtering regularized reconstructed digital breast tomosynthesis volume.

Develop a computer-aided detection (CADe) system for clustered microcalcifications in digital breast tomosynthesis (DBT) volume enhanced with multiscale bilateral filtering (MSBF) regularization. With Institutional Review Board approval and written informed consent, two-view DBT of 154 breasts, of which 116 had biopsy-proven microcalcification (MC) clusters and 38 were free of MCs, was imaged with a General Electric GEN2 prototype DBT system. The DBT volumes were reconstructed with MSBF-regularized simultaneous algebraic reconstruction technique (SART) that was designed to enhance MCs and reduce background noise while preserving the quality of other tissue structures. The contrast-to-noise ratio (CNR) of MCs was further improved with enhancement-modulated calcification response (EMCR) preprocessing, which combined multiscale Hessian response to enhance MCs by shape and bandpass filtering to remove the low-frequency structured background. MC candidates were then located in the EMCR volume using iterative thresholding and segmented by adaptive region growing. Two sets of potential MC objects, cluster centroid objects and MC seed objects, were generated and the CNR of each object was calculated. The number of candidates in each set was controlled based on the breast volume. Dynamic clustering around the centroid objects grouped the MC candidates to form clusters. Adaptive criteria were designed to reduce false positive (FP) clusters based on the size, CNR values and the number of MCs in the cluster, cluster shape, and cluster based maximum intensity projection. Free-response receiver operating characteristic (FROC) and jackknife alternative FROC (JAFROC) analyses were used to assess the performance and compare with that of a previous study. Unpaired two-tailed t-test showed a significant increase (p < 0.0001) in the ratio of CNRs for MCs with and without MSBF regularization compared to similar ratios for FPs. For view-based detection, a sensitivity of 85% was achieved at an FP rate of 2.16 per DBT volume. For case-based detection, a sensitivity of 85% was achieved at an FP rate of 0.85 per DBT volume. JAFROC analysis showed a significant improvement in the performance of the current CADe system compared to that of our previous system (p = 0.003). MBSF regularized SART reconstruction enhances MCs. The enhancement in the signals, in combination with properly designed adaptive threshold criteria, effective MC feature analysis, and false positive reduction techniques, leads to a significant improvement in the detection of clustered MCs in DBT.

An optimised patient-specific approach to administration of contrast agent for CT pulmonary angiography

To investigate pulmonary vasculature opacification during CTPA using an optimised patient-specific protocol for administering contrast agent. CTPA was performed on 200 patients with suspected PE. Patients were assigned to two protocol groups: protocol A, fixed 80 ml contrast agent; protocol B used a patient-specific approach. The mean cross-sectional opacification profile of 8 central and 11 peripheral pulmonary arteries and veins was measured and the arteriovenous contrast ratio (AVCR) calculated. Protocols were compared using Mann-Whitney U non-parametric statistics. Jack-knife alternative free-response receiver-operating characteristic (JAFROC) analyses assessed diagnostic efficacy. Interobserver variations were investigated using kappa methods. A number of pulmonary arteries demonstrated increases in opacification (P < 0.03) for protocol B compared to A, whilst opacification in the heart and veins was reduced in protocol B (P = 0.05). Increased AVCR in protocol B compared with A was observed at all anatomic locations (P < 0.0002). Increased JAFROC (P < 0.0002) and kappa variation were observed with protocol B (κ = 0.78) compared to A (κ = 0.25). Mean contrast volume was reduced in protocol B (33 ± 9 ml) compared to A (80 ± 1 ml). Significant improvements in visualisation of the pulmonary vasculature can be achieved with a low volume of contrast agent using injection timing based on a patient-specific contrast formula. • Optimal opacification of the pulmonary arteries is essential for CT pulmonary angiography. • Matching timing with vessel dynamics significantly improves vessel opacification. • This leads to increased arterial opacification and reduced venous opacification. • This can also lead to a reduced volume of contrast agent.

Comparison of Dual-Energy Subtraction and Electronic Bone Suppression Combined With Computer-Aided Detection on Chest Radiographs: Effect on Human Observers' Performance in Nodule Detection

The objective of our study was to compare the effect of dual-energy subtraction and bone suppression software alone and in combination with computer-aided detection (CAD) on the performance of human observers in lung nodule detection. One hundred one patients with from one to five lung nodules measuring 5-29 mm and 42 subjects with no nodules were retrospectively selected and randomized. Three independent radiologists marked suspicious-appearing lesions on the original chest radiographs, dual-energy subtraction images, and bone-suppressed images before and after postprocessing with CAD. Marks of the observers and CAD marks were compared with CT as the reference standard. Data were analyzed using nonparametric tests and the jackknife alternative free-response receiver operating characteristic (JAFROC) method. Using dual-energy subtraction alone (p = 0.0198) or CAD alone (p = 0.0095) improved the detection rate compared with using the original conventional chest radiograph. The combination of bone suppression and CAD provided the highest sensitivity (51.6%) and the original nonenhanced conventional chest radiograph alone provided the lowest (46.9%; p = 0.0049). Dual-energy subtraction and bone suppression provided the same false-positive (p = 0.2702) and true-positive (p = 0.8451) rates. Up to 22.9% of lesions were found only by the CAD program and were missed by the readers. JAFROC showed no difference in the performance between modalities (p = 0.2742-0.5442). Dual-energy subtraction and the electronic bone suppression program used in this study provided similar detection rates for pulmonary nodules. Additionally, CAD alone or combined with bone suppression can significantly improve the sensitivity of human observers for pulmonary nodule detection.

Model-Based Iterative Reconstruction Technique for Ultralow-Dose Chest CT

The purpose of this study was to evaluate whether model-based iterative reconstruction (MBIR) enables dose reduction over adaptive iterative reconstruction (ASIR) while maintaining diagnostic performance. In this institutional review board-approved and Health Insurance Portability and Accountability Act-compliant study, 59 patients (mean [SD] age, 64.7 [13.4] years) gave informed consent to undergo reference-, low-, and ultralow-dose chest computed tomography (CT) with 64-row multidetector CT. The reference- and low-dose CT involved the use of automatic tube current modulation with fixed noise indices (31.5 and 70.44 at 0.625 mm, respectively) and were reconstructed with 50% ASIR-filtered back projection blending. The ultralow-dose CT was acquired with a fixed tube current-time product of 5 mA s and reconstructed with MBIR. Two radiologists evaluated 2.5- and 0.625-mm-slice-thick axial images from low-dose ASIR and ultralow-dose MBIR, recorded the pattern of each nodule candidate, and assigned each a confidence score. A reference standard was established by a consensus panel of 2 different radiologists, who identified 84 noncalcified nodules with diameters of 4 mm or greater on reference-dose ASIR (ground-glass opacity, n = 18; partly solid, n = 11; solid, n = 55). Sensitivity in nodule detection was assessed using the McNemar test. Jackknife alternative free-response receiver operating characteristic (JAFROC) analysis was applied to assess the results including confidence scores. Compared with the low-dose CT, a 78.1% decrease in dose-length product was seen with the ultralow-dose CT. No significant differences were observed between the low-dose ASIR and the ultralow-dose MBIR for overall nodule detection in sensitivity (P = 0.48-0.69) or the JAFROC analysis (P = 0.57). Likewise, no significant differences were seen for ground-glass opacity, partly solid, or solid nodule detection in sensitivity (P = 0.08-0.65) or the JAFROC analysis (P = 0.21-0.90). Model-based iterative reconstruction enables nearly an 80% reduction in radiation dose for chest CT from a low-dose level to an ultralow-dose level, without affecting nodule detectability.

Accurate localization of incidental findings on the computed tomography attenuation correction image

This observer performance study assessed lesion detection in the computed tomography attenuation correction image, as would be produced for myocardial perfusion imaging over a tube current (mA) range. A static anthropomorphic chest phantom containing simulated pulmonary lesions was scanned using the four available mA values (1, 1.5, 2 and 2.5) on a GE Infinia Hawkeye 4. All other computed tomography acquisition parameters remained constant throughout. Twenty-seven cases showing zero to four lesions were produced for a free-response receiver-operating characteristic method. Image observations were completed using our novel web-based ROCView software under controlled conditions. The Jackknife alternative free-response receiver-operating characteristic (JAFROC) figure of merit was used for significance testing, wherein a difference in lesion detection performance was considered significant at P values less than 0.05. Twenty readers with varying computed tomography experience (0-24 years) evaluated 108 images using an ordinal scale to score confidence. The JAFROC analysis showed that there was no statistically significant difference in performance between mA values (P=0.439) for this sample of observers. In conclusion, no significant difference in lesion detection performance was seen between the mA values. This suggests that there is no value in using anything other than the lowest mA value for the investigation of incidental extracardiac findings.

MR Imaging in Patients with Suspected Liver Metastases: Value of Liver-Specific Contrast Agent Gadoxetic Acid

ObjectiveTo compare the diagnostic performance of gadoxetic acid-enhanced magnetic resonance (MR) imaging with that of triple-phase multidetector-row computed tomography (MDCT) in the detection of liver metastasis.Materials and MethodsOur institutional review board approved this retrospective study and waived informed consent. The study population consisted of 51 patients with hepatic metastases and 62 patients with benign hepatic lesions, who underwent triple-phase MDCT and gadoxetic acid-enhanced MRI within one month. Two radiologists independently and randomly reviewed MDCT and MRI images regarding the presence and probability of liver metastasis. In order to determine additional value of hepatobiliary-phase (HBP), the dynamic-MRI set alone and combined dynamic-and-HBP set were evaluated, respectively. The standard of reference was a combination of pathology diagnosis and follow-up imaging. For each reader, diagnostic accuracy was compared using the jackknife alternative free-response receiver-operating-characteristic (JAFROC).ResultsFor both readers, average JAFROC figure-of-merit (FOM) was significantly higher on the MR image sets than on the MDCT images: average FOM was 0.582 on the MDCT, 0.788 on the dynamic-MRI set and 0.847 on the combined HBP set, respectively (p < 0.0001). The differences were more prominent for small (≤ 1 cm) lesions: average FOM values were 0.433 on MDCT, 0.711 on the dynamic-MRI set and 0.828 on the combined HBP set, respectively (p < 0.0001). Sensitivity increased significantly with the addition of HBP in gadoxetic acid-enhanced MR imaging (p < 0.0001).ConclusionGadoxetic acid-enhanced MRI shows a better performance than triple-phase MDCT for the detection of hepatic metastasis, especially for small (≤ 1 cm) lesions.

Added value of 80 kVp images to averaged 120 kVp images in the detection of hepatocellular carcinomas in liver transplantation candidates using dual-source dual-energy MDCT: Results of JAFROC analysis

To assess the added value of 80 kVp images to weighted average 120 kVp images for detecting hepatocellular carcinomas (HCCs) using dual-source, dual-energy MDCT. Forty-one HCCs in 42 patients who underwent liver transplantation (LT) were included. All patients underwent quadruple-phase CT using a 64-row dual-source, dual-energy MDCT with 80 kVp and 140 kVp. For 120 kVp, a linear blending ratio of 0.3 was chosen. Interval reviews for both simulated 120 kVp images without and with pure 80 kVp data were performed independently by two radiologists. They detected HCCs using a 4-point confidence scale. Tumor-to-liver contrast-to-noise ratio (CNR) was calculated and compared between the 80 kVp and simulated 120 kVp images. The additional diagnostic value of 80 kVp images was evaluated by jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis. There were 41 HCCs on pathology and 37 of the 41 HCCs were depicted on CT scan. The mean CNR of the 37 HCCs in late arterial and portal-phase images was significantly better in the 80 kVp images than in 120 kVp images. The average JAFROC figure of merit, however, was not significantly improved when 80 kVp was added. Furthermore, the number of false-positives was significantly increased in reader 1 when adding 80kVp data. The addition of 80 kVp CT images to simulated 120 kVp images did not significantly improve the detection of HCCs despite of the significantly better CNR of 80 kVp images.

Consistency of methods for analysing location-specific data

Although the receiver operating characteristic (ROC) method is the acknowledged gold-standard for imaging system assessment, it ignores localisation information and differentiation between multiple abnormalities per case. As the free-response ROC (FROC) method uses localisation information and more closely resembles the clinical reporting process, it is being increasingly used. A number of methods have been proposed to analyse the data that result from an FROC study: jackknife alternative FROC (JAFROC) and a variant termed JAFROC1, initial detection and candidate analysis (IDCA) and ROC analysis via the reduction of the multiple ratings on a case to a single rating. The focus of this paper was to compare JAFROC1, IDCA and the ROC analysis methods using a clinical FROC human data set. All methods agreed on the ordering of the modalities and all yielded statistically significant differences of the figures-of-merit, i.e. p < 0.05. Both IDCA and JAFROC1 yielded much smaller p-values than ROC. The results are consistent with a recent simulation-based validation study comparing these and other methods. In conclusion, IDCA or JAFROC1 analysis of FROC human data may be superior at detecting modality differences than ROC analysis.

A status report on free-response analysis

The purpose of this paper is to summarise recent progress in free-response receiver operating characteristic (FROC) methodology. These are: (1) jackknife alternative FROC analysis including recent extensions and alternative methods; (2) the search-model simulator that enables validation and objective comparison of different methods of analysing the data; (3) case-based analysis that has the potential of greater clinical relevance than conventional free-response analysis; (4) a method for collectively analysing the multiple lesion types in an image (e.g. microcalcifications, masses and architectural distortions); (5) a method for sample-size estimation for FROC studies; and (6) a method for determining an objective proximity criterion, namely how close must a mark be to a true lesion in order to credit the observer for a true localisation. FROC analysis is being increasingly used to evaluate the imaging systems and understanding of recent progress should help researchers conduct better FROC studies.

Usefulness of the application of the BLADE technique to reduce motion artifacts on navigation‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver

To evaluate the effects of the application of the BLADE (Siemens, Siemens Medical Systems, Erlangen, Germany) technique, a technique to reduce motion artifacts, on navigator-triggered prospective acquisition correction (PACE) T2-weighted MRI (T2WI) of the liver. Twenty-three consecutive patients with a total of 57 localized hepatic diseases (39 malignant, 18 benign) and 57 patients without hepatic lesion underwent MR study during eupnea. The images were assessed quantitatively by calculating the liver-lesion contrast. Two subjective analyses were also performed. Two observers independently assessed the image quality and the confidence level of the detection and characterization of hepatic nodules using a five-point scale. Statistical analysis was performed with the Wilcoxon matched-pairs test except for the diagnostic performance evaluated with jackknife alternative free-response receiver operating characteristic (JAFROC) analysis. There was no significant difference in the mean liver-lesion contrast between the PACE T2WI with BLADE (T2WI-BLADE) (mean +/- SD = 0.29 +/- 0.14) and that without BLADE (0.30 +/- 0.14) (P = 0.39). Visual assessment of PACE T2WI-BLADE (4.8 +/- 0.47) was superior to that without BLADE (4.3 +/- 0.8) (P < 0.0001), although there were no significant differences in detecting and characterizing hepatic lesions using JAFROC analysis. The BLADE technique could improve image quality by reducing motion artifacts on hepatic MRI without affecting the diagnostic performance.

Quantitative CT Color Mapping of the Arterial Enhancement Fraction of the Liver to Detect Hepatocellular Carcinoma

To investigate the diagnostic value of quantitative determination and three-dimensional color mapping of the arterial enhancement fraction (AEF) of the liver for the detection of hepatocellular carcinoma (HCC). This retrospective study was approved by the institutional review board; informed consent was waived. Eighty-two patients (mean age, 56.2 years +/- 10.7 [standard deviation]), 69 men (mean age, 57.1 years +/- 10.0) and 13 women (mean age, 51.6 years +/- 13.6), were followed-up for HCC or liver cirrhosis by using available multiphasic multidetector computed tomographic (CT) scans. Quantitative AEF color maps (the ratio of the attenuation increment during the arterial phase to the attenuation increment during the portal venous phase) of the whole liver were created from routine CT images by using prototypic software. Three radiologists independently analyzed a multiphasic CT image set; 4 weeks later, to avoid any potential recall bias, they independently analyzed a combined image set of the quantitative color maps and the multiphasic CT images. The additional diagnostic value of the color mapping was evaluated by means of jackknife alternative free-response receiver-operating characteristic (JAFROC) analysis. The mean AEF of HCCs (75.6 +/- 13.3) was significantly higher than that of liver parenchyma (23.4 +/- 8.2) (P < .001). The average JAFROC figure of merit was 0.861 on the initial multiphasic CT image set. This increased to 0.933 on the second session with the combined image set (P < .05). The mean sensitivity for HCC detection increased from 71.7% with the multiphasic CT image set to 88.8% with the combined image set. Quantitative color mapping of the AEF can increase the sensitivity and diagnostic performance of multiphasic multidetector CT for detecting HCC. Supplementamaterial:http://radiology.rsnajnls.org/cgi/content/full/250/2/425/DC1http://radiology.rsnajnls.org/cgi/content/full/250/2/425/DC2http://radiology.rsnajnls.org/cgi/content/full/250/2/425/DC3