Jean-Paul Beregi

Dose reduction with iterative reconstruction: Optimization of CT protocols in clinical practice

OBJECTIVESnTo create an adaptable and global approach for optimizing MDCT protocols by evaluating the influence of acquisition parameters and Iterative Reconstruction (IR) on dose reduction and image quality.nnnMATERIALS AND METHODSnMDCT acquisitions were performed on quality image phantom by varying kVp, mAs, and pitch for the same collimation. The raw data were reconstructed by FBP and Sinogram Affirmed Iterative Reconstruction (SAFIRE) with different reconstruction kernel and thickness. A total of 4032 combinations of parameters were obtained. Indices of quality image (image noise, NCT, CNR, SNR, NPS and MTF) were analyzed. We developed a software in order to facilitate the optimization between dose reduction and image quality. Its outcomes were verified on an adult anthropomorphic phantom.nnnRESULTSnDose reduction resulted in the increase of image noise and the decrease of SNR and CNR. The use of IR improved these indices for the same dose without affecting NCT and MTF. The image validation was performed by the anthropomorphic phantom. The software proposed combinations of parameters to reduce doses while keeping indices of the image quality adequate. We observed a CTDIvol reduction between -44% and -83% as compared to the French diagnostic reference levels (DRL) for different anatomical localization.nnnCONCLUSIONnThe software developed in this study may help radiologists in selecting adequate combinations of parameters that allows to obtain an appropriate image with dose reduction.

Dose reduction with iterative reconstruction in multi-detector CT: What is the impact on deformation of circular structures in phantom study?

OBJECTIVESnTo evaluate the distortion of circular structures induced by the increased image noise related to dose reduction and to assess the effect of iterative reconstruction (IR).nnnMETHODSnMDCT acquisitions were performed with 120xa0kVp for 200/100/60/40/20mAs with 100%/50%/30%/20%/10% of dose. Raw data were reconstructed by filtered back projection (FBP) and with two IR strengths. Image quality indices referred to water and acrylic were measured on a quality image phantom. Areas, perimeters, circularity were measured on the circular inserts of 4.8, 7.9 and 11.1mm on a morphological phantom.nnnRESULTSnDose reduction resulted in increased image noise and in decreased signal to noise ratio and contrast to noise ratio. IR improved these indices for the same dose without affecting the signal (number CT) and spatial resolution (modulation transfer function). The values of area, perimeter and circularity were altered compared to the actual value and the inserts were visually deformed with the dose reduction. IR improved these three parameters. Image quality indices, areas, perimeters and circularity of inserts were similar between the acquisition at 100% of the dose in FBP, 50% in strength-3 and 30% in strength-5 with different curves of noise power spectrum.nnnCONCLUSIONnIR associated to 70% of dose reduction modifies the images smooth (NPS) but maintains adequate image quality indices without causing distortions of circular structures.

CT dose reduction using Automatic Exposure Control and iterative reconstruction: A chest paediatric phantoms study.

PURPOSEnTo evaluate the impact of Automatic Exposure Control (AEC) on radiation dose and image quality in paediatric chest scans (MDCT), with or without iterative reconstruction (IR).nnnMETHODSnThree anthropomorphic phantoms representing children aged one, five and 10-year-old were explored using AEC system (CARE Dose 4D) with five modulation strength options. For each phantom, six acquisitions were carried out: one with fixed mAs (without AEC) and five each with different modulation strength. Raw data were reconstructed with Filtered Back Projection (FBP) and with two distinct levels of IR using soft and strong kernels. Dose reduction and image quality indices (Noise, SNR, CNR) were measured in lung and soft tissues. Noise Power Spectrum (NPS) was evaluated with a Catphan 600 phantom.nnnRESULTSnThe use of AEC produced a significant dose reduction (p<0.01) for all anthropomorphic sizes employed. According to the modulation strength applied, dose delivered was reduced from 43% to 91%. This pattern led to significantly increased noise (p<0.01) and reduced SNR and CNR (p<0.01). However, IR was able to improve these indices. The use of AEC/IR preserved image quality indices with a lower dose delivered. Doses were reduced from 39% to 58% for the one-year-old phantom, from 46% to 63% for the five-year-old phantom, and from 58% to 74% for the 10-year-old phantom. In addition, AEC/IR changed the patterns of NPS curves in amplitude and in spatial frequency.nnnCONCLUSIONSnIn chest paediatric MDCT, the use of AEC with IR allows one to obtain a significant dose reduction while maintaining constant image quality indices.

Ultra-low-dose chest CT with iterative reconstruction does not alter anatomical image quality

PURPOSEnTo evaluate the effect of dose reduction with iterative reconstruction (IR) on image quality of chest CT scan.nnnMATERIALS AND METHODSnEighteen human cadavers had chest CT with one reference CT protocol (RP-CT; 120kVp/200mAs) and two protocols with dose reduction: low-dose-CT (LD-CT; 120kVp/40mAs) and ultra-low-dose CT (ULD-CT; 120kVp/10mAs). Data were reconstructed with filter-back-projection (FBP) for RP-CT and with FBP and IR (sinogram affirmed iterative reconstruction [SAFIRE®]) algorithm for LD-CT and ULD-CT. Volume CT dose index (CTDIvol) were recorded. The signal-to-noise (SNR), contrast-to-noise (CNR) ratios of LD-CT and ULD-CT and quantitative parameters were compared to RP-CT. Two radiologists reviewed the CT examinations assessed independently the quality of anatomical structures and expressed a confidence level using a 2-point scale (50% and 95%).nnnRESULTSnCTDIvol was 2.69xa0mGy for LD-CT (-80%; P<0.01) and 0.67xa0mGy for ULD-CT (-95%; P<0.01) as compared to 13.42xa0mGy for RP-CT. SNR and CNR were significantly decreased (P<0.01) for LD-CT and ULD-CT, but IR improved these values satisfactorily. No significant differences were observed for quantitative measurements. Radiologists rated excellent/good the RP-CT and LD-CT images, whereas good/fair the ULD-CT images. Confidence level for subjective anatomical analysis was 95% for all protocols.nnnCONCLUSIONSnDose reduction with a dose lower than 1xa0mGy, used in conjunction with IR allows performing chest CT examinations that provide a high quality of anatomical structures.

Diffusion Tensor Imaging in Patients with Glioblastoma Multiforme Using the Supertoroidal Model

Purpose Diffusion Tensor Imaging (DTI) is a powerful imaging technique that has led to improvements in the diagnosis and prognosis of cerebral lesions and neurosurgical guidance for tumor resection. Traditional tensor modeling, however, has difficulties in differentiating tumor-infiltrated regions and peritumoral edema. Here, we describe the supertoroidal model, which incorporates an increase in surface genus and a continuum of toroidal shapes to improve upon the characterization of Glioblastoma multiforme (GBM). Materials and Methods DTI brain datasets of 18 individuals with GBM and 18 normal subjects were acquired using a 3T scanner. A supertoroidal model of the diffusion tensor and two new diffusion tensor invariants, one to evaluate diffusivity, the toroidal volume (TV), and one to evaluate anisotropy, the toroidal curvature (TC), were applied and evaluated in the characterization of GBM brain tumors. TV and TC were compared with the mean diffusivity (MD) and fractional anisotropy (FA) indices inside the tumor, surrounding edema, as well as contralateral to the lesions, in the white matter (WM) and gray matter (GM). Results The supertoroidal model enhanced the borders between tumors and surrounding structures, refined the boundaries between WM and GM, and revealed the heterogeneity inherent to tumor-infiltrated tissue. Both MD and TV demonstrated high intensities in the tumor, with lower values in the surrounding edema, which in turn were higher than those of unaffected brain parenchyma. Both TC and FA were effective in revealing the structural degradation of WM tracts. Conclusions Our findings indicate that the supertoroidal model enables effective tensor visualization as well as quantitative scalar maps that improve the understanding of the underlying tissue structure properties. Hence, this approach has the potential to enhance diagnosis, preoperative planning, and intraoperative image guidance during surgical management of brain lesions.

Diffusion tensor imaging in patients with obstetric antiphospholipid syndrome without neuropsychiatric symptoms

ObjectivesTo evaluate white matter (WM) integrity in neurologically asymptomatic antiphospholipid syndrome (APS) using diffusion tensor imaging (DTI) in women with no thrombotic history but with pregnancy loss.MethodsImaging was performed with a 3xa0T scanner using structural MRI (T1-weighted, fluid attenuation inversion recovery [FLAIR]) and DTI sequences in 66 women with APS and a control group of 17 women. Women with APS were further categorized as positive for lupus anticoagulant (LA) and/or aβ2GPI-G antibodies (LA/aβ2GPI-G-positive, Nu2009=u200929) or negative (LA/aβ2GPI-G-negative, Nu2009=u200937) for both. Tract-based spatial statistics of standard DTI-based indices were compared among groups.ResultsWomen with APS had significantly lower fractional anisotropy (pu2009<u20090.05) associated with higher mean diffusivity and radial diffusivity compared to the control group. There was a stronger association of abnormal DTI features among women positive for LA and/or aβ2GPI-IgG antibodies than those who were negative.ConclusionsDTI appears sensitive to subtle WM changes in women with APS with no thrombotic history but with pregnancy loss, compatible with alterations in axonal structure and in the myelin sheath. The preferential association of abnormal DTI features with the two most pathogenic aPLAbs reinforces the pathophysiological relevance of our findings.Key Points• APS women exhibited lower FA and higher MD and RD than controls.• WM impairments are more severe in patients with positive LA or aβ2GPI-IgG.• An association exists between abnormal DTI features and LA or aβ2GPI-IgG positivity.• Diffusion tensor imaging detects microstructural white matter abnormalities in APS women.

Diagnostic performance of a low dose triple rule-out CT angiography using SAFIRE in emergency department.

OBJECTIVESnTo compare the diagnostic performance of triple rule out CT angiography (TRO-CTA) at 100kVp using sinogram affirmed iterative reconstruction (SAFIRE) with TRO-CTA at 120kVp using filtered back projection (FBP) in patients with acute chest pain.nnnMETHODSnConsecutive non-prepared patients from a single radiological emergency department, referred for acute chest pain evaluation with TRO-CTA, were randomly assigned to two different TRO-CTA protocols. Fifty patients (66% men; mean age, 66.6±19.0 [SD] years [range: 24-97years]) had TRO-CTA at 120kVp with FBP and 97 patients (67% men; mean age, 62.8±17.9 [SD] years [range: 24-93years]) had TRO-CTA at 100kVp with SAFIRE. Two radiologists reviewed the TRO-CTA images for pathologic findings and degree of diagnostic confidence. Image noise, vessel attenuation value, signal-to-noise and contrast-to-noise ratios in five main thoracic arteries were measured for objective and subjective analysis.nnnRESULTSnA total of 147 patients (98 men, 49 women; mean age, 64.7±18.4 [SD] [range, 24-97years) were included with good diagnostic confidence and equivalent pathological findings between the two TRO-CTA protocols. Objective and subjective analysis were identical between protocols and radiologists, except for vessel attenuation in the ascending aorta (P=0.02) and image noise in the pulmonary trunk (P=0.04). The effective radiation dose decreased significantly by 34% in the low dose TRO-CTA using SAFIRE protocol (5.7±2.7 vs 8.6±6.1mSv; P=4.7×10-6).nnnCONCLUSIONSnLow dose TRO-CTA protocol using SAFIRE allows a high confidence diagnostic level with the benefit of a 34% radiation dose decrease compared with a standard TRO-CTA protocol using FBP.

Imaging of tumors and tumor-like lesions of the knee

Tumors and tumor-like lesions of the knee are common conditions. Because the synovial membrane covers a large part of the knee, tumors and tumor-like lesions of the knee are mostly synovial. Magnetic resonance imaging (MRI) plays a major role in the assessment and characterization of these lesions. However, the diagnostic approach of these lesions must be performed systematically. First, the lesion must be precisely located, and then the anatomical structure involved must be determined. Finally, clinical background that includes the age of the patient, frequency of the disease and, if any, associated signs as well as MRI characteristics must be analyzed. In this review, we describe the anatomy of the knee and its compartments and provide a description of the main tumors and tumor-like lesions of the knee. We present a diagnostic approach based on the location within the knee of the lesions and the anatomical structures involved.

Characterization of vascular tree architecture using the Tokunaga taxonomy

The diagnosis of cardiovascular disease is usually assisted by resonance angiography (MRA) or computed tomography angiography (CTA) imaging. The identification of abnormal vascular architecture from angiographic three-dimensional images is therefore crucial to the diagnosis of cardiovascular disease. Automated detection and quantification of vascular structure and architecture thus holds significant clinical value. In this work, we employ a Lindenmayer system to represent vascular trees from angiographic images and describe a quantitative measure based on the Tokunaga taxonomy to differentiate vascular architectures. Synthetic vessel architectures with varying bifurcation patterns were compared and results showed that this architectural measure is proportional to the level of branching. In real MRA images, this measure was able to differentiate between normal and abnormal intracerebral vasculature containing an aneurysm. Hence, this methodology not only allows for compact representation of vascular architectures but also provides a quantitative metric of bifurcation complexity, which has the potential to characterize different types of vascular abnormalities.

Assessment of patient's peak skin dose during abdominopelvic embolization using radiochromic (Gafchromic) films

PURPOSEnTo assess the value of the routine use of radiochromic films in abdominopelvic embolization procedures to improve patient follow-up.nnnMETHODSnA total of 55xa0patients who underwent transcatheter abdominopelvic embolization were prospectively included. Six types of procedures were evaluated including hepatic chemoembolization (HCE), gonadal veins embolization (GVE), uterine elective embolization (UEE), uterine urgent embolization (UUE), abdominal elective embolization (AEE), and abdominal urgent embolization (AUE). Dosimetric indicators (DIs) such as air-kerma (AK) and kerma-area-product (KAP) were collected and peak skin dose (PSD) was measured with radiochromic films. Correlations between PSD and DIs were searched for.nnnRESULTSnThe mean (±standard deviation [SD]) PSD for the various procedures were: 1033±502xa0mGy for HCE; 476±271xa0mGy for GVE; 460±171 mGy for UEE; 531±263xa0mGy for UUE; 708±896xa0mGy for AEE; 683±392xa0mGy for AUE. Strong correlations were observed between PSD and DIs (r=0.974 for AK and r=0.925 for KAP). PSD was>2Gy in one procedure and all procedures (7/132) procedures resulted in AK>2Gy, mostly for HCE and AEE.nnnCONCLUSIONnDosimetry using radiochromic film is only appropriate for HCE, AEE and AUE, whereas dose-mapping systems present a more suitable solution for all embolizations including those with AK that occasionally exceed 2Gy.