Akos Varga-Szemes

Dual-Energy Computed Tomography Angiography of the Lower Extremity Runoff: Impact of Noise-Optimized Virtual Monochromatic Imaging on Image Quality and Diagnostic Accuracy.

ObjectiveThe aim of this study was to evaluate the impact of a noise-optimized virtual monochromatic imaging algorithm (VMI+) on image quality and diagnostic accuracy at dual-energy computed tomography angiography (CTA) of the lower extremity runoff. Materials and MethodsThis retrospective Health Insurance Portability and Accountability Act–compliant study was approved by the local institutional review board. We evaluated dual-energy CTA studies of the lower extremity runoff in 48 patients (16 women; mean age, 63.3 ± 13.8 years) performed on a third-generation dual-source CT system. Images were reconstructed with standard linear blending (F_0.5), VMI+, and traditional monochromatic (VMI) algorithms at 40 to 120 keV in 10-keV intervals. Vascular attenuation and image noise in 18 artery segments were measured; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Five-point scales were used to subjectively evaluate vascular attenuation and image noise. In a subgroup of 21 patients who underwent additional invasive catheter angiography, diagnostic accuracy for the detection of significant stenosis (≥50% lumen restriction) of F_0.5, 50-keV VMI+, and 60-keV VMI data sets were assessed. ResultsObjective image quality metrics were highest in the 40- and 50-keV VMI+ series (SNR: 20.2 ± 10.7 and 19.0 ± 9.5, respectively; CNR: 18.5 ± 10.3 and 16.8 ± 9.1, respectively) and were significantly (all P < 0.001) higher than in the corresponding VMI data sets (SNR: 8.7 ± 4.1 and 10.8 ± 5.0; CNR: 8.0 ± 4.0 and 9.6 ± 4.9) and F_0.5 series (SNR: 10.7 ± 4.4; CNR: 8.3 ± 4.1). Subjective assessment of attenuation was highest in the 40- and 50-keV VMI and VMI+ image series (range, 4.84–4.91), superior to F_0.5 (4.07; P < 0.001). Corresponding subjective noise assessment was superior for 50-keV VMI+ (4.71; all P < 0.001) compared with VMI (2.60) and F_0.5 (4.11). Sensitivity and specificity for detection of 50% or greater stenoses were highest in VMI+ reconstructions (92% and 95%, respectively), significantly higher compared with standard F_0.5 (87% and 90%; both P ⩽ 0.02). ConclusionsImage reconstruction using low-kiloelectron volt VMI+ improves image quality and diagnostic accuracy compared with traditional VMI technique and standard linear blending for evaluation of the lower extremity runoff using dual-energy CTA.

CT Myocardial Perfusion Imaging

OBJECTIVE. CT myocardial perfusion imaging is rapidly becoming an important adjunct to coronary CT angiography for the anatomic and functional assessment of coronary artery disease with a single modality. Existing techniques for CT myocardial perfusion imaging include static techniques, which provide a snapshot of the myocardial blood pool, and dynamic techniques. CONCLUSION. This review provides a systematic overview of the presently available approaches for the assessment of myocardial perfusion at CT, including diagnostic accuracy and limitations.

Cinematic Rendering in CT: A Novel, Lifelike 3D Visualization Technique

OBJECTIVE The purpose of this article is to present an overview of cinematic rendering, illustrating its potential advantages and applications. CONCLUSION Volume-rendered reconstruction, obtaining 3D visualization from original CT datasets, is increasingly used by physicians and medical educators in various clinical and educational scenarios. Cinematic rendering is a novel 3D rendering algorithm that simulates the propagation and interaction of light rays as they pass through the volumetric data, showing a more photorealistic representation of 3D images than achieved with standard volume rendering.

Absolute Versus Relative Myocardial Blood Flow by Dynamic CT Myocardial Perfusion Imaging in Patients With Anatomic Coronary Artery Disease

OBJECTIVE The purpose of this study was to evaluate differences in the diagnostic accuracy of absolute and relative territorial myocardial blood flow (MBF) derived from stress dynamic CT myocardial perfusion imaging (MPI) for the detection of significant coronary artery stenosis. MATERIALS AND METHODS Dynamic CT MPI and coronary CT angiography (CTA) datasets from a multicenter registry of 137 patients (mean age, 60.9 ± 8.4 years; 88 men) with suspected or known coronary artery disease were retrospectively analyzed. For each coronary territory, absolute MBF and the MBF relative to remote myocardium (MBF ratio) were calculated. Coronary CTA datasets were visually assessed for significant stenosis (≥ 50% luminal narrowing) in consensus by two observers. RESULTS Significant stenosis was detected in 137 of 411 (33.3%) vessels. Mean absolute MBF and MBF ratio were statistically significantly lower in territories supplied by arteries with stenosis (80.7 ± 33.7 vs 140.0 ± 38.4 mL/100 mL/min and 0.52 vs 0.89, respectively; both p < 0.0001). ROC analysis showed better discrimination by MBF ratio than by absolute MBF (AUC, 0.925 vs 0.882; p = 0.0022) and increased sensitivity (90.7% vs 82.4%; p < 0.04) and specificity (93.1% vs 80.5%; p < 0.03) for MBF ratio and absolute MBF cutoff values of 0.71 or less and 103 mL/100 mL/min or less, respectively. CONCLUSION In stress dynamic CT MPI, relative MBF provides superior diagnostic accuracy compared with absolute territorial MBF values for coronary CTA-detected significant coronary artery stenosis.

Approaches to ultra-low radiation dose coronary artery calcium scoring based on 3rd generation dual-source CT: A phantom study

OBJECTIVES To investigate to what extent 3rd generation dual-source computed tomography (DSCT) can reduce radiation dose in coronary artery calcium scoring. METHODS Image acquisition was performed using a stationary calcification phantom. Prospectively electrocardiogram (ECG)-triggered 120 kV sequential, and 120 and Sn100 kV ultra-high pitch (UHP) acquisitions were performed with different tube currents (80, 60, 40, 20 mA). Images were reconstructed using filtered back projection (FBP) and 3rd generation iterative reconstruction (IR). Contrast-to-noise ratio (CNR), Agatston score, calcium volume, and radiation dose were assessed. For statistical analysis Friedman tests and Wilcoxon rank sum tests were used. RESULTS Even at reduced tube currents, the three acquisition techniques did not show significant differences in Agatston score (p=0.4) or calcium volume (p=0.08) with FBP reconstruction. Calcium volumes were significantly lower for 3rd generation IR compared to FBP reconstructions (p<0.01). CTDIvol for the 120 kV sequential, 120 and Sn100 kV UHP acquisitions at 80 and 20 mA were 1.2-0.37, 0.48-0.17, and 0.07-0.02 mGy, respectively. CONCLUSION 3rd generation DSCT enabled a reduction of tube current in both the sequential and UHP acquisitions without significantly affecting coronary calcium scoring. Tin filtered 100 kV scanning may allow accurate quantification of calcium score without correction of the HU threshold.

Technical prerequisites and imaging protocols for dynamic and dual energy myocardial perfusion imaging.

Coronary CT angiography (CCTA) is an established imaging technique used for the non-invasive morphological assessment of coronary artery disease. As in invasive coronary angiography, CCTA anatomical assessment of coronary stenosis does not adequately predict hemodynamic relevance. However, recent technical improvements provide the possibility of CT myocardial perfusion imaging (CTMPI). Two distinct CT techniques are currently available for myocardial perfusion assessment: static CT myocardial perfusion imaging (sCTMPI), with single- or dual-energy modality, and dynamic CT myocardial perfusion imaging (dCTMPI). The combination of CCTA morphological assessment and CTMPI functional evaluation holds promise for achieving a comprehensive assessment of coronary artery anatomy and myocardial perfusion using a single image modality.

Differentiation of acute and four-week old myocardial infarct with Gd(ABE-DTTA)-enhanced CMR.

BackgroundStandard extracellular cardiovascular magnetic resonance (CMR) contrast agents (CA) do not provide differentiation between acute and older myocardial infarcts (MI). The purpose of this study was to develop a method for differentiation between acute and older myocardial infarct using myocardial late-enhancement (LE) CMR by a new, low molecular weight contrast agent.Dogs (n = 6) were studied in a closed-chest, reperfused, double myocardial infarct model. Myocardial infarcts were generated by occluding the Left Anterior Descending (LAD) coronary artery with an angioplasty balloon for 180 min, and four weeks later occluding the Left Circumflex (LCx) coronary artery for 180 min. LE images were obtained on day 3 and day 4 after second myocardial infarct, using Gd(DTPA) (standard extracellular contrast agent) and Gd(ABE-DTTA) (new, low molecular weight contrast agent), respectively. Triphenyltetrazolium chloride (TTC) histomorphometry validated existence and location of infarcts. Hematoxylin-eosin and Massons trichrome staining provided histologic evaluation of infarcts.ResultsGd(ABE-DTTA) or Gd(DTPA) highlighted the acute infarct, whereas the four-week old infarct was visualized by Gd(DTPA), but not by Gd(ABE-DTTA). With Gd(ABE-DTTA), the mean ± SD signal intensity enhancement (SIE) was 366 ± 166% and 24 ± 59% in the acute infarct and the four-week old infarct, respectively (P < 0.05). The latter did not differ significantly from signal intensity in healthy myocardium (P = NS). Gd(DTPA) produced signal intensity enhancements which were similar in acute (431 ± 124%) and four-week old infarcts (400 ± 124%, P = NS), and not statistically different from the Gd(ABE-DTTA)-induced SIE in acute infarct. The existence and localization of both infarcts were confirmed by triphenyltetrazolium chloride (TTC). Histologic evaluation demonstrated coagulation necrosis, inflammation, and multiple foci of calcification in the four day old infarct, while the late subacute infarct showed granulation tissue and early collagen deposition.ConclusionsLate enhancement CMR with separate administrations of standard extracellular contrast agent, Gd(DTPA), and the new low molecular weight contrast agent, Gd(ABE-DTTA), differentiates between acute and late subacute infarct in a reperfused, double infarct, canine model.

Virtual unenhanced imaging of the liver with third-generation dual-source dual-energy CT and advanced modeled iterative reconstruction

OBJECTIVES To compare image quality and diagnostic accuracy for the detection of liver lesions of virtual unenhanced (VU) images based on third-generation dual-source dual- energy computed tomography (DECT) compared to conventional unenhanced (CU) images. METHODS Thirty patients underwent triphasic abdominal CT consisting of single-energy CU (120kV, 147 ref.mAs) and dual-energy CT arterial and portal-venous phase acquisitions (100/Sn150kV, 180/90 ref.mAs). VU images were generated from arterial (AVU) and portal venous (PVU) phases. CU, AVU and PVU datasets were reconstructed. Quantitative image quality analysis was performed and two abdominal radiologists independently analyzed all datasets to evaluate image quality and identify liver lesions. Radiation dose was recorded and potential radiation dose reduction was estimated. RESULTS Image quality was rated diagnostic in 100% of the VU datasets. The mean subjective image quality of the CU datasets was higher than that of VU images (p<0.0001). No significant difference was observed in the mean attenuation values of the liver parenchyma (p>0.99) and hypoattenuating liver lesions (p≥0.21) between CU, AVU and PVU. However, a significant reduction in the attenuation values of calcified lesions (p<0.0001), metallic clips (p<0.0001) and gallstones (p≤0.047) was observed in the AVU and PVU images compared with CU images. A total of 122 liver lesions were found in 25 patients. VU images were more sensitive than CU images for detection of small hypoattenuating liver lesions (≤1cm). However, CU images were more sensitive than VU for calcified liver lesions. The mean radiation dose reduction achievable by avoiding the unenhanced acquisition was 32.9%±1.1% (p<0.01). CONCLUSIONS Third-generation DSCT VU images of the liver provide diagnostic image quality and improve small (≤1cm) liver lesion detection; however calcified liver lesions can be missed due to complete subtraction.

Myocardial perfusion imaging with dual energy CT

Dual-energy CT (DECT) enables simultaneous use of two different tube voltages, thus different x-ray absorption characteristics are acquired in the same anatomic location with two different X-ray spectra. The various DECT techniques allow material decomposition and mapping of the iodine distribution within the myocardium. Static dual-energy myocardial perfusion imaging (sCTMPI) using pharmacological stress agents demonstrate myocardial ischemia by single snapshot images of myocardial iodine distribution. sCTMPI gives incremental values to coronary artery stenosis detected on coronary CT angiography (CCTA) by showing consequent reversible or fixed myocardial perfusion defects. The comprehensive acquisition of CCTA and sCTMPI offers extensive morphological and functional evaluation of coronary artery disease. Recent studies have revealed that dual-energy sCTMPI shows promising diagnostic accuracy for the detection of hemodynamically significant coronary artery disease compared to single-photon emission computed tomography, invasive coronary angiography, and cardiac MRI. The aim of this review is to present currently available DECT techniques for static myocardial perfusion imaging and recent clinical applications and ongoing investigations.

Percent infarct mapping for delayed contrast enhancement magnetic resonance imaging to quantify myocardial viability by Gd(DTPA).

To demonstrate the advantages of signal intensity percent‐infarct‐mapping (SI‐PIM) using the standard delayed enhancement (DE) acquisition in assessing viability following myocardial infarction (MI). SI‐PIM quantifies MI density with a voxel‐by‐voxel resolution in clinically used DE images.