Iterative Model Reconstruction Technique Research Articles

Optimized categorization algorithm of coronary artery calcification score on non-gated chest low-dose CT screening using iterative model reconstruction technique

ObjectivesTo investigate the optimized categorization algorithm of coronary artery calcification score (CACS) for more accurate risk assessment on non-gated chest low-dose CT (LDCT) screening using iterative model reconstruction (IMR) technique. MethodsWe enrolled 102 patients who required coronary artery CTA examination and had coronary artery calcification (CAC) in this study. The CACS on non-gated LDCT and ECG-gated CT images were both measured by Agatston analysis software on Philips workstation. ResultsAccording to the original algorithm (1–100, 100–400 and >400), the CACS measured by non-gated LDCT scan showed a good agreement with ECG-gated CT scan (weighted kappa value of 0.602, P < 0.05). Two ROC curves were drawn to evaluate the accuracy of CACS categorization. The cutoff values were 87.44 and 255.26 respectively. Based on the best diagnostic cutoff value, the CACS measured by the non-gated LDCT scan showed an excellent agreement with ECG-gated CT scan (weighted kappa value of 0.781, P < 0.05). ConclusionsThe CACS on non-gated LDCT may have been underestimated. We therefore developed an optimized categorization algorithm of non-gated CACS in this study.

2 Milisievert Low Dose Dedicated Breast CT with Iterative Model Reconstruction Technique in Evaluation of Breast Mass: Feasibility Study in Comparison with MRI

Objective To investigate the feasibility of low dose dedicated computed tomography (CT) with IMR technique compared with magnetic resonance imaging (MRI) in preoperative evaluation of breast cancer. Methods Dedicated CT and breast MRI were performed in 21 patients with diagnosed breast mass for preoperative evaluation. A dedicated protocol combined with chest diagnostic CT and dynamic scans of breast was developed with the use of IMR technique as well as optimization of scan parameters to ensure acceptable radiation dose. Image quality evaluations of CT images were performed using a five-point scale. The number, site and size (maximum diameter) of breast lesion were recorded respectively in CT and MRI images. The enhancement patterns of breast lesion were classified to 3 types (washout, plateau, and persistence) according to time intensity curve derived from CT and time signal curve derived from MRI, respectively. Pearson’s correlation, Bland-Altman analysis, and Cohen’s kappa test were used for statistical assessment. Results The mean effective radiation dose of dedicated breast CT, with the image quality diagnostic acceptable for evaluation of breast lesion and pulmonary structures, was (2.15±0.39) mSv, which was no more than a routine chest diagnostic CT. Results of breast lesion number and lesion site obtained by CT and MRI was consistent, with a total of 24 lesions detected in 21 patients. The mean lesion size was (26.5±12.1) mm in CT and (26.1±12.9) mm in MR, respectively. CT showed an excellent correlation with MRI for lesion size (r=0.99, n=24, p<0.0001). Limits of agreement determined by Bland-Altman analysis for lesion extent was (-3.0mm, 3.8mm). Good agreement was observed between CT and MRI for lesion enhancement patterns (kappa value = 0.936, p=0.000). Conclusion Dedicated breast CT imaging with acceptable radiation dose enabled diagnostic image quality and showed good agreement with breast MR imaging in preoperative evaluation of breast cancer.

Usefulness of a Low Tube Voltage: Knowledge-Based Iterative Model Reconstruction Algorithm for Computed Tomography Venography.

The objective of this study was to evaluate the use of 80-kVp scans with knowledge-based iterative model reconstruction (IMR) for computed tomography venography (CTV). This prospective study received institutional review board approval; a previous informed consent was obtained from all participants. We enrolled 30 patients with suspected deep venous thrombosis or pulmonary embolism who were to undergo 80-kVp CTV studies. The images were reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR), and IMR. The venous attenuation, image noise, and contrast-to-noise ratio at the iliac, femoral, and popliteal veins were compared on FBP, HIR, and IMR images. We performed qualitative image analysis (image noise, image contrast, image sharpness, streak artifacts, and overall image quality) of the 3 reconstruction methods and measured their reconstruction times. There was no significant difference in venous attenuation among the 3 reconstruction methods (P > 0.05). On IMR images, the image noise was lowest at all 3 venous locations, and the contrast-to-noise ratio was highest. Qualitative evaluation scores were also highest for IMR images. The reconstruction time for FBP, HIR, and IMR imaging was 25.4 ± 1.9 seconds, 43.3 ± 3.3 seconds, and 78.7 ± 6.0 seconds, respectively. At clinically acceptable reconstruction times, 80-kVp CTV using the IMR technique yielded better qualitative and quantitative image quality than HIR and FBP.

Knowledge-based iterative model reconstruction technique in computed tomography of lumbar spine lowers radiation dose and improves tissue differentiation for patients with lower back pain

PurposeTo evaluate the image quality and diagnostic confidence of reduced-dose computed tomography (CT) of the lumbar spine (L-spine) reconstructed with knowledge-based iterative model reconstruction (IMR). Materials and methodsProspectively, group A consisted of 55 patients imaged with standard acquisition reconstructed with filtered back-projection. Group B consisted of 58 patients imaged with half tube current, reconstructed with hybrid iterative reconstruction (iDose4) in Group B1 and knowledge-based IMR in Group B2. Signal-to-noise ratio (SNR) of different regions, the contrast-to-noise ratio between the intervetebral disc (IVD) and dural sac (D-D CNR), and subjective image quality of different regions were compared. Higher strength IMR was also compared in spinal stenosis cases. ResultsThe SNR of the psoas muscle and D-D CNR were significantly higher in the IMR group. Except for the facet joint, subjective image quality of other regions including IVD, intervertebral foramen (IVF), dural sac, peridural fat, ligmentum flavum, and overall diagnostic acceptability were best for the IMR group. Diagnostic confidence of narrowing IVF and IVD was good (kappa=0.58–0.85). Higher strength IMR delineated IVD better in spinal stenosis cases. ConclusionLower dose CT of L-spine reconstructed with IMR demonstrates better tissue differentiation than iDose4 and standard dose CT with FBP.

Sub-milliSievert ultralow-dose CT colonography with iterative model reconstruction technique

Purpose. The purpose of this study was to evaluate the technical and diagnostic performance of sub-milliSievert ultralow-dose (ULD) CT colonograpy (CTC) in the detection of colonic and extracolonic lesions.Materials and Methods. CTC with standard dose (SD) and ULD acquisitions of 64 matched patients, half of them with colonic findings, were reconstructed with filtered back projection (FBP), hybrid (HIR) and iterative model reconstruction techniques (IMR). Image noise in six colonic segments, in the left psoas muscle and aorta were measured. Image quality of the left adrenal gland and of the colon in the endoscopic and 2D view was rated on a five point Likert scale by two observers, who also completed the reading of CTC for colonic and extracolonic findings.Results. The mean radiation dose estimate was 4.1 ± 1.4 mSv for SD and 0.86 ± 0.17 mSv for ULD for both positions (p < 0.0001). In ULD-IMR, SD-IMR and SD-HIR, the endoluminal noise was decreased in all colonic segments compared to SD-FBP (p < 0.001). There were 27 small (6–9 mm) and 17 large (≥10 mm) colonic lesions that were classified as sessile polyps (n = 38), flat lesions (n = 3), or as a mass (n = 3). Per patient sensitivity and specificity were 0.82 and 0.93 for ULD-FBP, 0.97 and 0.97 for ULD-HIR, 0.97 and 1.0 for ULD-IMR. Per polyp sensitivity was 0.84 for ULD-FBP, 0.98 for ULD-HIR, 0.98 for ULD-IMR. Significantly less extracolonic findings were detected in ULD-FBP and ULD-HIR, but in the E4 category by C-RADS (potentially important findings), the detection was similar.Conclusion. Both HIR and IMR are suitable for sub-milliSievert ULD CTC without sacrificing diagnostic performance of the study.

High-Quality Three-Dimensional Computed Tomography Angiography of Abdominal Viscera with Small Focal Spot, Low Tube Voltage, and Iterative Model Reconstruction Technique

Purpose: To evaluate the quality of three-dimensional (3D) CT angiography images of the abdominal viscera with small focal spot, low tube voltage, and iterative model reconstruction technique (IMR). Materials and Methods: Seven patients with suspected disease of the pancreatobiliary system had undergone CT with high-quality CTA protocol in the present study. There were 5 men and 2 women, ranging in age from 52 to 80 years (mean: 64 years). Results: Depiction of abdominal small artery, small portal vein was possible in all cases. In two cases that we were able to compare, it was superior to standard CTA in small vascular depiction in CTA made clearly in high quality protocol. Conclusions: Although the use of small focal spot, low tube voltage, and IMR can produce higher-quality images of abdominal vessels than standard CTA, this improvement is not significant at elevated radiation doses.

Ultra-low dose abdominal MDCT: Using a knowledge-based Iterative Model Reconstruction technique for substantial dose reduction in a prospective clinical study

PurposeTo assess lesion detection and image quality parameters of a knowledge-based Iterative Model Reconstruction (IMR) in reduced dose (RD) abdominal CT examinations. Materials and methodsThis IRB-approved prospective study included 82 abdominal CT examinations performed for 41 consecutive patients (mean age, 62±12 years; F:M 28:13) who underwent a RD CT (SSDE, 1.5mGy±0.4 [∼0.9mSv] at 120kV with 17–20mAs/slice) immediately after their standard dose (SD) CT exam (10mGy±3 [∼6mSv] at 120kV with automatic exposure control) on 256 MDCT (iCT, Philips Healthcare). SD data were reconstructed using filtered back projection (FBP). RD data were reconstructed with FBP and IMR. Four radiologists used a five-point scale (1=image quality better than SD CT to 5=image quality unacceptable) to assess both subjective image quality and artifacts. Lesions were first detected on RD FBP images. RD IMR and RD FBP images were then compared side-by-side to SD-FBP images in an independent, randomized and blinded fashion. Friedman's test and intraclass correlation coefficient were used for data analysis. Objective measurements included image noise and attenuation as well as noise spectral density (NSD) curves to assess the noise in frequency domain were obtained. In addition, a low-contrast phantom study was performed. ResultsAll true lesions (ranging from 32 to 55) on SD FBP images were detected on RD IMR images across all patients. RD FBP images were unacceptable for subjective image quality. Subjective ratings showed acceptable image quality for IMR for organ margins, soft-tissue structures, and retroperitoneal lymphadenopathy, compared to RD FBP in patients with a BMI ≤25kg/m2 (median-range, 2–3). Irrespective of patient BMI, subjective ratings for hepatic/renal cysts, stones and colonic diverticula were significantly better with RD IMR images (P<0.01). Objective image noise for RD FBP was 57–66% higher, and for RD IMR was 8–56% lower than that for SD-FBP (P<0.01). NSD showed significantly lower noise in the frequency domain with IMR in all patients compared to FBP. ConclusionIMR considerably improved both objective and subjective image quality parameters of RD abdominal CT images compared to FBP in patients with BMI less than or equal to 25kg/m2.