The Impact of Iterative Reconstruction in Low-Dose Computed Tomography on the Evaluation of Diffuse Interstitial Lung Disease

OBJECTIVE: To evaluate the impact of iterative reconstruction (IR) on the assessment of diffuse interstitial lung disease (DILD) using CT. MATERIALS AND METHODS: An American College of Radiology (ACR) phantom (module 4 to assess spatial resolution) was scanned with 10–100 effective mAs at 120 kVp. The images were reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), with blending ratios of 0%, 30%, 70% and 100%, and model-based iterative reconstruction (MBIR), and their spatial resolution was objectively assessed by the line pair structure method. The patient study was based on retrospective interpretation of prospectively acquired data, and it was approved by the institutional review board. Chest CT scans of 23 patients (mean age 64 years) were performed at 120 kVp using 1) standard dose protocol applying 142–275 mA with dose modulation (high-resolution computed tomography [HRCT]) and 2) low-dose protocol applying 20 mA (low dose CT, LDCT). HRCT images were reconstructed with FBP, and LDCT images were reconstructed using FBP, ASIR, and MBIR. Matching images were randomized and independently reviewed by chest radiologists. Subjective assessment of disease presence and radiological diagnosis was made on a 10-point scale. In addition, semi-quantitative results were compared for the extent of abnormalities estimated to the nearest 5% of parenchymal involvement. RESULTS: In the phantom study, ASIR was comparable to FBP in terms of spatial resolution. However, for MBIR, the spatial resolution was greatly decreased under 10 mA. In the patient study, the detection of the presence of disease was not significantly different. The values for area under the curve for detection of DILD by HRCT, FBP, ASIR, and MBIR were as follows: 0.978, 0.979, 0.972, and 0.963. LDCT images reconstructed with FBP, ASIR, and MBIR tended to underestimate reticular or honeycombing opacities (-2.8%, -4.1%, and -5.3%, respectively) and overestimate ground glass opacities (+4.6%, +8.9%, and +8.5%, respectively) compared to the HRCT images. However, the reconstruction methods did not differ with respect to radiologic diagnosis. CONCLUSION: The diagnostic performance of LDCT with MBIR was similar to that of HRCT in typical DILD cases. However, caution should be exercised when comparing disease extent, especially in follow-up studies with IR.

Adaptive Statistical Iterative Reconstruction-Applied Ultra-Low-Dose CT with Radiography-Comparable Radiation Dose: Usefulness for Lung Nodule Detection

OBJECTIVE: To assess the performance of adaptive statistical iterative reconstruction (ASIR)-applied ultra-low-dose CT (ULDCT) in detecting small lung nodules. MATERIALS AND METHODS: Thirty patients underwent both ULDCT and standard dose CT (SCT). After determining the reference standard nodules, five observers, blinded to the reference standard reading results, independently evaluated SCT and both subsets of ASIR- and filtered back projection (FBP)-driven ULDCT images. Data assessed by observers were compared statistically. RESULTS: Converted effective doses in SCT and ULDCT were 2.81 +/- 0.92 and 0.17 +/- 0.02 mSv, respectively. A total of 114 lung nodules were detected on SCT as a standard reference. There was no statistically significant difference in sensitivity between ASIR-driven ULDCT and SCT for three out of the five observers (p = 0.678, 0.735, < 0.01, 0.038, and < 0.868 for observers 1, 2, 3, 4, and 5, respectively). The sensitivity of FBP-driven ULDCT was significantly lower than that of ASIR-driven ULDCT in three out of the five observers (p < 0.01 for three observers, and p = 0.064 and 0.146 for two observers). In jackknife alternative free-response receiver operating characteristic analysis, the mean values of figure-of-merit (FOM) for FBP, ASIR-driven ULDCT, and SCT were 0.682, 0.772, and 0.821, respectively, and there were no significant differences in FOM values between ASIR-driven ULDCT and SCT (p = 0.11), but the FOM value of FBP-driven ULDCT was significantly lower than that of ASIR-driven ULDCT and SCT (p = 0.01 and 0.00). CONCLUSION: Adaptive statistical iterative reconstruction-driven ULDCT delivering a radiation dose of only 0.17 mSv offers acceptable sensitivity in nodule detection compared with SCT and has better performance than FBP-driven ULDCT.

Digital Tomosynthesis of the Chest: Comparison of Patient Exposure Dose and Image Quality between Standard Default Setting and Low Dose Setting

OBJECTIVE: To determine the optimum low dose (LD) digital tomosynthesis (DT) setting, and to compared the image quality of the LD DT with that of the standard default (SD) DT. MATERIALS AND METHODS: Nine DT settings, by changing tube voltage, copper filter, and dose ratio, were performed for determining the LD setting. Among combinations of DT setting, a condition providing the lowest radiation dose was determined. Eighty artificial nodules less than 1 cm in diameter (subcentimeter nodules: 40, micronodules less than 4 mm: 40) were attached to a Styrofoam and a diaphragm of the phantom. Among these, 38 nodules were located at the periphery of the lung (thin area) and 42 nodules were located at the paravertebral or sub-diaphragmatic area (thick area). Four observers counted the number of nodules detected in the thick and thin areas. The detection sensitivity in SD and LD settings were calculated separately. Data were analyzed statistically. RESULTS: The lowest LD setting was a combination of 100 kVp, 0.3 mm additional copper filter, and a 1 : 5 dose ratio. The effective dose for the LD and SD settings were 62 microSv and 140 microSv, separately. A 56.7% dose reduction was achieved in the LD setting compared with the SD setting. Detection sensitivities were not different between the SD and the LD settings except between observers 1 and 2 for the detection of micronodules in the thick area. CONCLUSION: LD DT can be effective in nodule detection bigger than 4 mm without a significant decrease in image quality compared with SD DT.

Molecularly Targeted Therapy Using Bevacizumab for Non-Small Cell Lung Cancer: a Pilot Study for the New CT Response Criteria

OBJECTIVE: We wanted to compare the efficacy of the new CT response evaluation criteria for predicting the tumor progression-free survival (PFS) with that of RECIST 1.1 in non-small cell lung cancer (NSCLC) patients who were treated with bevacizumab. MATERIALS AND METHODS: Sixteen patients (M:F = 11:5; median age, 57 years) treated with bevacizumab and combined cytotoxic chemotherapeutic agents were selected for a retrospective analysis. The tumor response was assessed by four different methods, namely, by using RECIST 1.1 (RECIST), RECIST but measuring only the solid component of tumor (RECISTsolid), the alternative method reflecting tumor cavitation (the alternative method) and the combined criteria (the combined criteria) that evaluated both the changes of tumor size and attenuation. To evaluate the capabilities of the different measurement methods to predict the patient prognosis, the PFS were compared, using the log rank test, among the responder groups (complete response [CR], partial response [PR], stable disease [SD] and progressive disease [PD]) in terms of the four different methods. RESULTS: The overall (CR, PR or SD) response rates according to RECIST, RECISTsolid, the alternative method and the combined criteria were 81%, 88%, 81% and 85%, respectively. The confirmed response rates (CR or PR) were 19%, 19%, 50% and 54%, respectively. Although statistically not significant, the alternative method showed the biggest difference for predicting PFS among the three response groups (PR, SD and PD) (p = 0.07). RECIST and the alternative method showed a significant difference for predicting the prognosis between the good (PR or SD) and poor overall responders (p = 0.02). CONCLUSION: The response outcome evaluations using the three different CT response criteria that reflect tumor cavitation, the ground-glass opacity component and the attenuation changes in NSCLC patients treated with bevacizumab showed different results from that with using the traditional RECIST method.

Hypointense Hepatic Lesions Depicted on Gadobenate Dimeglumine-Enhanced Three-Hour Delayed Hepatobiliary-Phase MR Imaging: Differentiation between Benignancy and Malignancy

Gadobenate dimeglumine-enhanced magnetic resonance (MR) imaging simultaneously provides both morphological and functional information by the acquisition of dynamic and hepatobiliary-phase imaging. Focal lesions with no functioning hepatocytes, where hepatobiliary metabolism is blocked or inhibited, are generally unable to uptake and excrete gadobenate dimeglumine into the bile. Such lesions are typically malignant and usually appear hypointense as compared to the normal liver parenchyma as seen on hepatobiliary-phase imaging. However, various benign hepatic lesions may also be hypointense due to (a) the presence of no functioning hepatocytes, (b) damage to the functioning hepatocytes or (c) impairment of biliary function as depicted on hepatobiliary-phase imaging. All of these imaging features may result in recognition of the benign hepatic lesions as hepatic malignancies. As depicted on three-hour delayed hepatobiliary-phase imaging, peripheral iso/hyperintensity due to fibrotic tissue compared to the hypointense center with a fuzzy margin may be a clue for the presence of a benign hepatic lesion. In contrast, peripheral hypointensity due to rich tumoral cellularity compared to the center with a clear margin may favor an indication of the presence of a malignant hepatic lesion.

Chondrolipoma in the Pelvic Cavity: a Case Report

A chondrolipoma is an extremely rare form of a benign mesenchymal tumor containing mature cartilage and fatty tissue. Chondrolipomas may be found in almost any part of the body, particularly in the connective tissue of the breast, head and neck area, as well as in the skeletal muscle. However, to the best of our knowledge, chondrolipomas located in the pelvic cavity have not been reported. In this case report, we describe a case of a chondrolipoma in the pelvis, and show that it has its own characteristic imaging findings, which included the composition of fatty tissue and calcification in most parts, as well as some focal areas of chondroid tissue based on the CT and MR findings.

A Comparison between Dual-Exposure Dual-Energy Radiography and Standard Chest Radiography for the Diagnosis of Small Pulmonary Nodules

PURPOSE: To evaluate the utility of dual-exposure dual-energy radiography against the standard chest radiography in the discrimination of lung nodules and the presence of nodule calcification. MATERIALS AND METHODS: Twenty-nine patients with a total of 43 peripheral lung nodules were examined by dual-exposure dual-energy radiography (DER) and confirmed by a chest CT were included in the study. Of the identified peripheral lung nodules, 24 showed calcification and 19 did not. Further, 28 lesion-free regions from the same patient population were selected as negative controls. Two radiologists evaluated 71 marked locations using both standard chest radiographs (SR) and DER to determine whether the marked locations represented a true nodule, and whether nodule calcification was present. A continuous rating scale of 0-10 was used to represent each observer's confidence level. We calculated the areas under ROC curves (AUC) for SR alone and for DER, and performed a statistical analysis to compare the results. RESULTS: The ability to discriminate nodules was higher for DER than for SR. However, the was not statistically significant (p = 0.202). Inter-observer agreement was moderate regardless of if DER was used. The predictability of nodule calcification was significantly higher for DER compared to SR (p < .001). Moreover, inter-observer agreement was slight with SR alone but moderate with DER. CONCLUSION: DER, in conjunction with SR, has no additional benefit in small lung nodule discrimination but does provide a significant benefit in the characterization of nodule calcification.