Dual-Energy CT Vital Iodine Tumor Burden for Response Assessment in Patients With Metastatic GIST Undergoing TKI Therapy: Comparison With Standard CT and FDG PET/CT Criteria.

BACKGROUND. CT-based criteria for assessing the gastrointestinal stromal tumor (GIST) response to tyrosine kinase inhibitor (TKI) therapy are limited in part because tumor attenuation is influenced by treatment-related changes including hemorrhage and calcification. The iodine concentration may be less impacted by such changes. OBJECTIVE. The purpose of this study was to determine whether the dual-energy CT (DECT) vital iodine tumor burden (TB) allows improved differentiation between treatment responders and nonresponders among patients with metastatic GIST who are undergoing TKI therapy compared with established CT and PET/CT criteria. METHODS. An anthropomorphic phantom with spherical inserts mimicking GIST lesions of varying iodine concentrations and having nonenhancing central necrotic cores underwent DECT to determine a threshold iodine concentration. Forty patients (25 women and 15 men; median age, 57 years) who were treated with TKI for metastatic GIST were retrospectively evaluated. Patients underwent baseline and follow-up DECT and FDG PET/CT. Response assessment was performed using RECIST 1.1, modified Choi (mChoi) criteria, vascular tumor burden (VTB) criteria, DECT vital iodine TB criteria, and European Organization for Research and Treatment of Cancer (EORTC) PET criteria. DECT vital iodine TB criteria used the same percentage changes as RECIST 1.1 response categories. Progression-free survival was compared between responders and nonresponders for each response criterion by use of Cox proportional hazard ratios and Harrell C-indexes (i.e., concordance indexes). RESULTS. The phantom experiment identified a threshold of 0.5 mg/mL to differentiate vital from nonvital tissue. With use of the DECT vital iodine TB, median progression-free survival was significantly different between responders and nonresponders (623 vs 104 days; p < .001).. For nonresponders versus responders, the hazard ratio for disease progression for DECT vital iodine TB was 6.9 versus 7.6 for EORTC PET criteria, 3.3 for VTB criteria, 2.3 for RECIST 1.1, and 2.1 for mChoi criteria. The C-index was 0.74 for EORTC PET criteria, 0.73 for DECT vital iodine TB criteria, 0.67 for VTB criteria, 0.61 for RECIST 1.1, and 0.58 for mChoi criteria. The C-index was significantly greater for DECT vital iodine TB criteria than for RECIST 1.1 (p = .02) and mChoi criteria (p = .002), but it was not different from that for VTB and EORTC PET criteria (p > .05). CONCLUSION. DECT vital iodine TB criteria showed performance comparable to that of EORTC PET criteria and outperformed RECIST 1.1 and mChoi criteria for response assessment of metastatic GIST treated with TKI therapy. CLINICAL IMPACT. DECT vital iodine TB could help guide early management decisions in patients receiving TKI therapy.

Correlation of Iodine Quantification and FDG Uptake in Early Therapy Response Assessment of Non-small Cell Lung Cancer: Possible Benefit of Dual-energy CT Scan as an Integral Part of PET/CT Examination.

AIM: To compare iodine-related and fluorine-18 fluorodeoxyglucose (18F-FDG) parameters during staging of lung cancer as well as during early follow-up, while investigating potential use and possible substitutability in the assessment of therapeutic response or prediction. PATIENTS AND METHODS: Patients (n=45) with confirmed lung cancer underwent 18F-FDG positron-emission tomography (PET) using single-source dual-energy computed tomography was performed for staging and early follow-up. Correlation of FDG uptake and iodine-related parameters was assessed and comparison with therapy response was performed. RESULTS: A strong correlation was found between the volumetric FDG parameters metabolic tumour volume (MTV) and total lesion glycolysis (TLG) and iodine uptake (IU) in staging (IU vs. MTV: rs=0.894; p<0.001 and IU vs. TLG: rs=0.874; p<0.001) and follow-up (IU vs. MTV: rs=0.934, p<0.001 and IU vs. TLG: rs=0.935, p<0.001). We also found significant correlation of change in these values between timepoints. We observed a significant correlation of IU, MTV and TLG with early therapy response and IU was found as a possible strong predictor. CONCLUSION: Strong correlation of IU and volume-based FDG parameters was proved in staging, follow-up and change during therapy. Potential role of IU in prediction of early therapy-response was identified. Our study suggests a significant benefit of using the dual-energy computed tomography as a part of 18F-FDG PET/CT in patients with lung cancer.

Radiation dose reduction in parasinus CT by spectral shaping.

INTRODUCTION: Spectral shaping aims to narrow the X-ray spectrum of clinical CT. The aim of this study was to determine the image quality and the extent of radiation dose reduction that can be achieved by tin prefiltration for parasinus CT. METHODS: All scans were performed with a third generation dual-source CT scanner. A study protocol was designed using 100 kV tube voltage with tin prefiltration (200 mAs) that provides image noise levels comparable to a low-dose reference protocol using 100 kV without spectral shaping (25 mAs). One hundred consecutive patients were prospectively enrolled and randomly assigned to the study or control group. All patients signed written informed consent. The study protocol was approved by the local Institutional Review Board and applies to the HIPAA. Subjective and objective image quality (attenuation values, image noise, and contrast-to-noise ratio (CNR)) were assessed. Radiation exposure was assessed as volumetric CT dose index, and effective dose was estimated. Mann-Whitney U test was performed for radiation exposure and for image noise comparison. RESULTS: All scans were of diagnostic image quality. Image noise in air, in the retrobulbar fat, and in the eye globe was comparable between both groups (all p > 0.05). CNReye globe/air did not differ significantly between both groups (p = 0.7). Radiation exposure (1.7 vs. 2.1 mGy, p < 0.01) and effective dose (0.055 vs. 0.066 mSv, p < 0.01) were significantly reduced in the study group. CONCLUSION: Radiation dose can be further reduced by 17% for low-dose parasinus CT by tin prefiltration maintaining diagnostic image quality.

Dual-Phase Dual-Energy CT in Patients Treated with Erlotinib for Advanced Non-Small Cell Lung Cancer: Possible Benefits of Iodine Quantification in Response Assessment.

OBJECTIVES: To investigate the relationship of dual-phase dual-energy CT (DE-CT) and tumour size in the evaluation of the response to anti-EGFR therapy in patients with advanced non-small cell lung cancer (NSCLC). METHODS: Dual-phase DE-CT was performed in 31 patients with NSCLC before the onset of anti-EGFR (erlotinib) therapy and as follow-up (mean 8 weeks). Iodine uptake (IU; mg/mL) was quantified using prototype software in arterial and venous phases; arterial enhancement fraction (AEF) was calculated. The change of IU before and after therapy onset was compared with anatomical evaluation in maximal transverse diameter and volume (responders vs. non-responders). RESULTS: A significant decrease of IU in venous phase was proved in responders according to all anatomical parameters (p=0.002-0.016). In groups of non-responders, a significant change of IU was not proved with variable trends of development. The most significant change was observed using the anatomical parameter of volume (cut-off 73 %). A significant difference of percentage change in AEF was proved between responding and non-responders (p=0.019-0.043). CONCLUSION: Dual-phase DE-CT with iodine uptake quantification is a feasible method with potential benefit in advanced assessment of anti-EGFR therapy response. We demonstrated a decrease in vascularization in the responding primary tumours and non-significant variable development of vascularization in non-responding tumours. KEY POINTS: • Dual-phase DE-CT is feasible for vascularization assessment of NSCLC with anti-EGFR therapy. • There was a significant decrease of iodine uptake in responding tumours. • There was a non-significant and variable development in non-responding tumours. • There was significant difference of AEF percentage change between responders and non-responders.

Dual-phase dual-energy CT in patients with lung cancer: assessment of the additional value of iodine quantification in lymph node therapy response.

OBJECTIVES: To investigate the potential contribution of iodine uptake calculation from dual-phase dual-energy CT (DE-CT) for lymph node staging and therapy response monitoring in lung cancer patients. METHODS: Retrospective analysis of 27 patients with non-small cell lung carcinoma (NSCLC), who underwent dual-phase DE-CT before and after chemotherapy, was performed. Iodine uptake (mg/mL) and total iodine uptake (mg) were calculated using prototype software in the early (arterial) and late (venous) post-contrast circulatory phase in 110 mediastinal lymph nodes. The arterial enhancement fraction (AEF) was calculated and compared with lymph node size and response to chemotherapy. RESULTS: A significant difference of AEF was observed between enlarged (90.4%; 32.3-238.5%) and non-enlarged (72.7%; -37.5-237.5%) lymph nodes (p = 0.044) before treatment onset. A significantly different change of AEF in responding (decrease of 26.3%; p = 0.022) and non-responding (increase of 43.0%; p = 0.031) lymph nodes was demonstrated. A higher value of AEF before treatment was observed in lymph nodes with subsequent favourable response (88.6% vs. 77.7%; p = 0.122), but this difference did not reach statistical significance. CONCLUSIONS: The dual-phase DE-CT examination with quantification of ratio of early and late post-contrast iodine uptake is a feasible and promising method for the functional evaluation of mediastinal lymph nodes including therapy response assessment. KEY POINTS: • Dual-phase DE-CT is beneficial for mediastinal lymph node assessment in NSCLC. • Arterial to venous iodine uptake ratio was higher in enlarged lymph nodes. • Change of arterial enhancement fraction correlated to therapy response.

Assessment of an advanced image-based technique to calculate virtual monoenergetic computed tomographic images from a dual-energy examination to improve contrast-to-noise ratio in examinations using iodinated contrast media.

INTRODUCTION: Following the trend of low-radiation dose computed tomographic (CT) imaging, concerns regarding the detectability of low-contrast lesions have been growing. The goal of this research was to evaluate whether a new image-based algorithm (Mono+) for virtual monoenergetic imaging with a dual-energy CT scanner can improve the contrast-to-noise ratio (CNR) and conspicuity of these low-contrast objects when using iodinated contrast media. MATERIALS AND METHODS: Four circular phantoms of different diameter (10-40 cm) with an iodine insert at the center were scanned at a fixed radiation dose with different single- (80, 100, 120 kV) and dual-energy protocols (80/140 kV, 80/140 Sn kV, 100/140 Sn kV) using a dual-source CT system. In addition, an anthropomorphic abdominal phantom with different low-contrast lesions was scanned with the settings previously mentioned but also at only a half and a quarter of the initial dose. Dual-energy data were processed, and virtual monoenergetic images (range, 40-190 keV) were generated. Beside the established technique, a newly developed prototype algorithm to calculate monoenergetic images (Mono+) was used. To avoid noise increase at lower calculated energies, which is a known drawback of virtual monoenergetic images at low kilo electron-volt, a regional spatial frequency-based recombination of the high signal at lower energies and the superior noise properties at medium energies is performed to optimize CNR in case of Mono+ images. The CNR and low-contrast detectability were evaluated. RESULTS: For all phantom sizes, the Mono+ technique provided increasing iodine CNR with decreasing kilo electron-volt, with the optimum CNR obtained at the lowest energy level of 40 keV. For all investigated phantom sizes, CNR of Mono+ images at low kilo electron-volt was superior to the CNR in single-energy images at an equivalent radiation dose and even higher than the CNR obtained with 80-kV protocols. In case of the anthropomorphic phantom, low-contrast detectability in monoenergetic images was, for all settings, similar to the circular phantoms, best for the voltage combination 80/140 Sn kV, irrespective of the dose level. For all dual-energy voltage combinations, the Mono+ algorithm led to superior results compared with single-energy imaging. DISCUSSION: With regard to optimized iodine CNR, it is more efficient to perform dual-energy scans and compute virtual monoenergetic images at 40 keV using the Mono+ technique than to perform low kilovolt scans. Given the improved CNR, the Mono+ algorithm could be very useful in improving both detection and differential diagnosis of abdominal lesions, specifically low-contrast lesions, as well as in other anatomical regions where improved iodine CNR is beneficial.

Assessment of an iterative reconstruction algorithm (SAFIRE) on image quality in pediatric cardiac CT datasets.

BACKGROUND: Pediatric cardiac patients often undergo repeat diagnostic testing, resulting in relatively high cumulative medical radiation exposure. Low-dose CT scanning techniques used to decrease radiation exposure may result in reduced image quality. OBJECTIVE: This study evaluates a prototype iterative reconstruction algorithm, sinogram-affirmed iterative reconstruction (SAFIRE), to determine the effect on qualitative and quantitative measures of image quality in pediatric cardiac CT datasets, compared with a standard weighted filtered back projection (wFBP) algorithm. METHODS: Seventy-four datasets obtained on a 128-slice dual-source CT system were evaluated for image quality using both the wFBP and the prototype iterative reconstruction algorithm. Contrast, noise, contrast-to-noise ratio, signal-to-noise ratio, and qualitative image quality were compared between groups. Data were analyzed as medians and 25th and 75th percentiles, and groups were compared with the use of the Wilcoxon singed-rank test or k sample equality of medians test. RESULTS: There was a 34% decrease in noise, a 41% increase in contrast-to-noise ratio, and a 56% increase in signal-to-noise ratio in the prototype iterative reconstruction, compared with wFBP. All differences were statistically significant (P < 0.001). Qualitative measures of image noise and noise texture were also improved in the iterative reconstruction group (P < 0.001 for both). Diagnostic confidence was similar between reconstruction techniques. Median scan dose length product was 15.5 mGy · cm. CONCLUSION: The prototype iterative reconstruction algorithm studied significantly reduces image noise and improves qualitative and quantitative measures of image quality in low-dose pediatric CT datasets, compared with standard wFBP.