Consistency of Monoenergetic Attenuation Measurements for a Clinical Dual-Source Photon-Counting Detector CT System Across Scanning Paradigms: A Phantom Study.

BACKGROUND. Use of virtual monoenergetic images (VMIs) from multienergy CT scans can mitigate inconsistencies in traditional attenuation measurements that result from variation in scan-related factors. Photon-counting detector (PCD) CT systems produce VMIs as standard image output under flexible scanning conditions. OBJECTIVE. The purpose of this article was to evaluate the consistency of monoenergetic attenuation measurements obtained from a clinical PCD CT scanner across a spectrum of scanning paradigms. METHODS. A phantom with 10 tissue-simulating inserts was imaged using a clinical dual-source PCD CT scanner. Nine scanning paradigms were obtained across combinations of tube voltages (90, 120, and 140 kVp) and image quality (IQ) levels (80, 145, and 180). Images were reconstructed at VMI levels of 50, 60, 70, and 80 keV. Consistency of attenuation measurements was assessed, using the 120 kVp with IQ level of 145 scanning paradigm as the reference scan. RESULTS. For all scanning paradigms, attenuation measurements showed intra-class correlation of 0.999 and higher with respect to the reference scan. Across inserts, mean bias relative to the reference scan ranged from -14.9 to 13.6 HU, -2.7 to 1.7 HU, and -3.9 to 3.8 HU at tube voltages of 90, 120, and 140 kVp, respectively; and from -14.9 to 13.6 HU, -6.4 to 3.8 HU, -3.7 to 1.4 HU, and -7.2 to 4.3 HU at VMI levels of 50, 60, 70, and 80 keV, respectively. Thus, mean bias did not exceed 5 HU for any insert at tube potentials of 120 kVp and 140 kVp, nor for any insert at a VMI level of 70 keV. At a VMI level of 50 keV and tube potential of 90 kVp, mean bias exceeded 5 HU for 14 of 30 possible combinations of inserts and scanning paradigms and exceeded 10 HU for four of 30 such combinations. At VMI levels of both 60 and 80 keV, mean bias exceeded 5 HU for only two combinations of inserts and scanning paradigms, all at a tube potential of 90 kVp. CONCLUSION. PCD CT generally provided consistent attenuation measurements across combinations of scanning paradigms and VMI levels. CLINICAL IMPACT. PCD CT may facilitate quantitative applications of CT data in clinical practice.

Real-time cardiac MRI with radial acquisition and k-space variant reduced-FOV reconstruction.

This work aims to demonstrate that radial acquisition with k-space variant reduced-FOV reconstruction can enable real-time cardiac MRI with an affordable computation cost. Due to non-uniform sampling, radial imaging requires k-space variant reconstruction for optimal performance. By converting radial parallel imaging reconstruction into the estimation of correlation functions with a previously-developed correlation imaging framework, Cartesian k-space may be reconstructed point-wisely based on parallel imaging relationship between every Cartesian datum and its neighboring radial samples. Furthermore, reduced-FOV correlation functions may be used to calculate a subset of Cartesian k-space data for image reconstruction within a small region of interest, making it possible to run real-time cardiac MRI with an affordable computation cost. In a stress cardiac test where the subject is imaged during biking with a heart rate of >100 bpm, this k-space variant reduced-FOV reconstruction is demonstrated in reference to several radial imaging techniques including gridding, GROG and SPIRiT. It is found that the k-space variant reconstruction outperforms gridding, GROG and SPIRiT in real-time imaging. The computation cost of reduced-FOV reconstruction is ~2 times higher than that of GROG. The presented work provides a practical solution to real-time cardiac MRI with radial acquisition and k-space variant reduced-FOV reconstruction in clinical settings.

CT pulmonary angiography in patients with acute or chronic renal insufficiency: Evaluation of a low dose contrast material protocol.

Adverse effects of intravenous contrast media (CM) in patients with renal risk factors and acute kidney injury are still controversially discussed. The aim of this study was to investigate whether dual-energy (DE) pulmonary CT angiography (CTPA) in combination with a noise optimized virtual monoenergetic imaging algorithm allows for a reduction of CM. This IRB-approved study comprised 150 patients with suspected pulmonary embolism (78 male; mean age 65 ± 17years). 50 patients with acute/chronic renal failure were examined on a 3rd generation dual-source CT with an optimized DE CTPA protocol and a low CM injection protocol (5.4 g iodine). 100 further patients were either examined with a standard CTPA protocol or a standard DE CTPA (32 g iodine). For the DE CTPA virtual monoenergetic spectral datasets (40-100 keV) were reconstructed. Main pulmonary arteries at 50 keV and peripheral pulmonary arteries at 40 keV datasets provided the highest contrast-to-noise-ratio (CNR) for both the standard DE CTPA and the optimized protocol, with significantly higher CNR values for the standard DE CTPA protocol (p < 0.05). No pulmonary embolism was missed on the optimized CM protocol. DE CTPA utilizing image reconstruction at 40/50 keV allowed for a reduction of 84% in iodine load while maintaining CNR, which is especially important in patients with acute/chronic renal failure.

Image Quality of 3rd Generation Spiral Cranial Dual-Source CT in Combination with an Advanced Model Iterative Reconstruction Technique: A Prospective Intra-Individual Comparison Study to Standard Sequential Cranial CT Using Identical Radiation Dose.

OBJECTIVES: To prospectively intra-individually compare image quality of a 3rd generation Dual-Source-CT (DSCT) spiral cranial CT (cCT) to a sequential 4-slice Multi-Slice-CT (MSCT) while maintaining identical intra-individual radiation dose levels. METHODS: 35 patients, who had a non-contrast enhanced sequential cCT examination on a 4-slice MDCT within the past 12 months, underwent a spiral cCT scan on a 3rd generation DSCT. CTDIvol identical to initial 4-slice MDCT was applied. Data was reconstructed using filtered backward projection (FBP) and 3rd-generation iterative reconstruction (IR) algorithm at 5 different IR strength levels. Two neuroradiologists independently evaluated subjective image quality using a 4-point Likert-scale and objective image quality was assessed in white matter and nucleus caudatus with signal-to-noise ratios (SNR) being subsequently calculated. RESULTS: Subjective image quality of all spiral cCT datasets was rated significantly higher compared to the 4-slice MDCT sequential acquisitions (p<0.05). Mean SNR was significantly higher in all spiral compared to sequential cCT datasets with mean SNR improvement of 61.65% (p*Bonferroni0.05<0.0024). Subjective image quality improved with increasing IR levels. CONCLUSION: Combination of 3rd-generation DSCT spiral cCT with an advanced model IR technique significantly improves subjective and objective image quality compared to a standard sequential cCT acquisition acquired at identical dose levels.

Initial results of a new generation dual source CT system using only an in-plane comb filter for ultra-high resolution temporal bone imaging.

OBJECTIVES: To prospectively evaluate radiation dose and image quality of a third generation dual-source CT (DSCT) without z-axis filter behind the patient for temporal bone CT. METHODS: Forty-five patients were either examined on a first, second, or third generation DSCT in an ultra-high-resolution (UHR) temporal bone-imaging mode. On the third generation DSCT system, the tighter focal spot of 0.2 mm(2) removes the necessity for an additional z-axis-filter, leading to an improved z-axis radiation dose efficiency. Images of 0.4 mm were reconstructed using standard filtered-back-projection or iterative reconstruction (IR) technique for previous generations of DSCT and a novel IR algorithm for the third generation DSCT. Radiation dose and image quality were compared between the three DSCT systems. RESULTS: The statistically significantly highest subjective and objective image quality was evaluated for the third generation DSCT when compared to the first or second generation DSCT systems (all p < 0.05). Total effective dose was 63%/39% lower for the third generation examination as compared to the first and second generation DSCT. CONCLUSIONS: Temporal bone imaging without z-axis-UHR-filter and a novel third generation IR algorithm allows for significantly higher image quality while lowering effective dose when compared to the first two generations of DSCTs. KEY POINTS: • Omitting the z-axis-filter allows a reduction in radiation dose of 50% • A smaller focal spot of 0.2 mm (2) significantly improves spatial resolution • Ultra-high-resolution temporal-bone-CT helps to gain diagnostic information of the middle/inner ear.

Closing in on the K edge: coronary CT angiography at 100, 80, and 70 kV-initial comparison of a second- versus a third-generation dual-source CT system.

PURPOSE: To prospectively evaluate radiation and contrast medium requirements for performing high-pitch coronary computed tomographic (CT) angiography at 70 kV using a third-generation dual-source CT system in comparison to a second-generation dual-source CT system. MATERIALS AND METHODS: All patients gave informed consent for this institutional review board-approved study. Forty-five patients (median age, 52 years; 27 men) were imaged in high-pitch mode with a third-generation dual-source CT system at 70 kV (n = 15) or with a second-generation dual-source CT system at 80 or 100 kV (n = 15 for each). Tube voltage was based on body mass index: 80 or 70 kV for less than 26 kg/m(2) versus 100 kV for 26-30 kg/m(2). For the 80- and 100-kV protocols, 80 mL of contrast material was injected, versus 45 mL for the 70-kV protocol. Data were reconstructed by using a second-generation iterative reconstruction algorithm for second-generation dual-source CT and a recently introduced third-generation iterative reconstruction algorithm for third-generation dual-source CT. Objective image quality was measured for various regions of interest, and subjective image quality was evaluated with a five-point Likert scale. RESULTS: The signal-to-noise ratio of the coronary CT angiography studies acquired with 70 kV was significantly higher (70 kV: 14.3-17.6 vs 80 kV: 7.1-12.9 vs 100 kV: 9.8-12.9; P < .0497) than those acquired with the other two protocols for all coronary arteries. Qualitative image quality analyses revealed no significant differences between the three CT angiography protocols (median score, 5; P > .05). The mean effective dose was 75% and 108% higher (0.92 mSv ± 0.3 [standard deviation] and 0.78 mSv ± 0.2 vs 0.44 mSv ± 0.1; P < .0001), respectively, for the 80- and 100-kV CT angiography protocols than for the 70-kV CT angiography protocol. CONCLUSION: In nonobese patients, third-generation high-pitch coronary dual-source CT angiography at 70 kV results in robust image quality for studying the coronary arteries, at significantly reduced radiation dose (0.44 mSv) and contrast medium volume (45 mL), thus enabling substantial radiation dose and contrast medium savings as compared with second-generation dual-source CT.

Objective and subjective image quality of liver parenchyma and hepatic metastases with virtual monoenergetic dual-source dual-energy CT reconstructions: an analysis in patients with gastrointestinal stromal tumor.

RATIONALE AND OBJECTIVES: To compare in dual-energy CT (DECT) conventionally reconstructed polyenergetic images (PEI) at 120 kVp to virtual monoenergetic images (MEI) at different kiloelectron volt (keV) levels for evaluation of liver and gastrointestinal stromal tumor (GIST) hepatic metastases with regard to objective (IQob) and subjective image quality (IQsub) assessed by two readers of varying experience. Image quality was correlated to patient size and compared between PEI and MEI. MATERIALS AND METHODS: From 50 examinations of 17 GIST patients (12 with hepatic metastases) undergoing abdominal dual-source DECT for staging, therapy monitoring or follow-up, PEI and nine MEI in 10-keV intervals from 40 to 120 keV were reconstructed. Liver contrast-to-noise ratios (CNR) and metastasis-to-liver ratios were calculated. MEI reconstructions with the highest IQob were compared to PEI for IQsub by one experienced reader (ER) and one inexperienced reader (IR). Patients' diameters were correlated to IQob and IQsub ratings. RESULTS: MEI at 70 keV had the highest IQob with equal liver CNR and metastasis-to-liver ratio compared to PEI. The ER rated 70-keV MEI and PEI equally high (median 4), whereas the IR rated IQsub best in 70-keV MEI (median 5). Unlike in PEI, IQsub ratings in 70-keV MEI were not correlated to patient size. CONCLUSIONS: MEI at 70 keV provided an IQob equivalent to PEI. Regarding the IR, IQsub was improved in 70-keV MEI compared to PEI and less dependent on patient size. Therefore, IRs might improve their diagnostic confidence in the assessment of hepatic GIST metastases by evaluating MEI reconstructions at 70 keV.

Diagnostic accuracy of cardiac computed tomography angiography for myocardial infarction.

AIM: To investigate diagnostic accuracy of high, low and mixed voltage dual energy computed tomography (DECT) for detection of prior myocardial infarction (MI). METHODS: Twenty-four consecutive patients (88% male, mean age 65 ± 11 years old) with clinically documented prior MI (> 6 mo) were prospectively recruited to undergo late phase DECT for characterization of their MI. Computed tomography (CT) examinations were performed using a dual source CT system (64-slice Definition or 128-slice Definition FLASH, Siemens Healthcare) with initial first pass and 10 min late phase image acquisitions. Using the 17-segment model, regional systolic function was analyzed using first pass CT as normal or abnormal (hypokinetic, akinetic, dyskinetic). Regions with abnormal systolic function were identified as infarct segments. Late phase DE scans were reconstructed into: 140 kVp, 100 kVp, mixed (120 kVp) images and iodine-only datasets. Using the same 17-segment model, each dataset was evaluated for possible (grade 2) or definite (grade 3) late phase myocardial enhancement abnormalities. Logistic regression for correlated data was used to compare reconstructions in terms of the accuracy for detecting infarct segments using late myocardial hyperenhancement scores. RESULTS: All patients reported prior history of documented myocardial infarction, with most occurring more than 5 years prior (n = 18; 75% of cohort). Fifty-five of 408 (13%) segments demonstrated abnormal wall motion and were classified as infarct. The remaining 353 segments were classified as non-infarcted segments. A total of 1692 segments were analyzed for late phase enhancement abnormalities, with 91 (5.5%) segments not interpretable due to artifact. Combined grades 2 and 3 compared to grade 3 only enhancement abnormalities demonstrated significantly higher sensitivity and similar specificity for detection of infarct segments for all reconstructions evaluated. Evaluation of different voltage acquisitions demonstrated the highest diagnostic performance for the 100 kVp reconstruction which had higher diagnostic accuracy (87%; 95%CI: 80%-90%), sensitivity (86%-93%; 95%CI: 54%-78%) and specificity (90%; 95%CI: 86%-93%) compared to the other reconstructions. For sensitivity, there were significant differences noted between 100 kVp vs 140 kVp (P < 0.0005), 100 kVp vs mixed (P < 0.0001), and 100 kVp vs iodine only (P < 0.005) using combined grade 2 and grade 3 perfusion abnormalities. For specificity, there were significant differences noted between 100 kVp vs 140 kVp (P < 0.005), and 100 kVp vs mixed (P < 0.01) using combined grades 2 and 3 perfusion abnormalities. CONCLUSION: Low voltage acquisition CT, 100 kVp in this study, demonstrates superior diagnostic performance when compared to higher and mixed voltage acquisitions for detection of prior MI.

Iodine quantification with dual-energy CT: phantom study and preliminary experience with renal masses.

OBJECTIVE: The purpose of this study was to validate the utility of dual-source dual-energy MDCT in quantifying iodine concentration in a phantom and in renal masses. MATERIALS AND METHODS: A series of tubes containing solutions of varying iodine concentration were imaged with dual-source dual-energy MDCT. Iodine concentration was calculated and compared with known iodine concentration. Single-phase contrast-enhanced dual-source dual-energy MDCT data on 15 patients with renal lesions then were assessed independently by two readers. Dual-energy postprocessing was used to generate iodine-only images. Regions of interest were placed on the iodine image over the lesion and, as a reference, over the aorta, for recording of iodine concentration in the lesion and in the aorta. Another radiologist determined lesion enhancement by comparing truly unenhanced with contrast-enhanced images. Mixed-model analysis of variance based on ranks was used to compare lesion types (simple cyst, hemorrhagic cyst, enhancing mass) in terms of lesion iodine concentration and lesion-to-aorta iodine ratio. RESULTS: In the phantom study, there was excellent correlation between calculated and true iodine concentration (R(2) = 0.998, p < 0.0001). In the patient study, 13 nonenhancing (10 simple and three hyperdense cysts) and eight enhancing renal masses were evaluated in 15 patients. The lesion iodine concentration and lesion-to-aorta iodine ratio in enhancing masses were significantly higher than in hyperdense and simple cysts (p < 0.0001). CONCLUSION: Iodine quantification with dual-source dual-energy MDCT is accurate in a phantom and can be used to determine the presence and concentration of iodine in a renal lesion. Characterization of renal masses may be possible with a single dual-source dual-energy MDCT acquisition without unenhanced images or reliance on a change in attenuation measurements.

Dual-energy MDCT: comparison of pulmonary artery enhancement on dedicated CT pulmonary angiography, routine and low contrast volume studies.

PURPOSE: The aim of this study was (a) to compare arterial enhancement in simultaneously acquired high- and low-kilovoltage images; and (b) to determine whether low tube-voltage imaging would permit PE evaluation on routine chest CT studies or CTPA studies performed with a low volume of contrast media. MATERIALS AND METHODS: We compared 20 CTPA studies (CTPA group), 20 routine thoracic CT studies (RT group) and 10 CTPA studies performed with reduced volume of contrast media (RC group). HU values were measured in all groups at 80 kVp and 140 kVp images in multiple pulmonary arterial segments bilaterally. The diagnostic quality of the central and peripheral vascular enhancement and the image noise were evaluated at both energies using a five-point scale. RESULTS: For all patients, the mean CT attenuation values were greater at 80 kVp than 140 kVp images (p<0.001). At 80 kVp, CTPA group attenuation values were greater than RT group (p=0.03) with a similar trend at 140 kVp (p=0.08). At both 140 kVp and 80 kVp, CTPA group attenuation values were greater than RC group (p=0.02 and p=0.03, respectively). Qualitative analysis showed that at 140 kVp CTPA studies had better global image quality scores than RT (p=0.003) and RC (p=0.001) groups. However, at 80 kVp, there was no significant difference of global image quality between CTPA and the other groups (p=0.4 and p=0.5, respectively). Although measurable image noise was greater at 80 kVp than 140 kVp (p<0.001), qualitative analysis revealed lower image noise at 80 kVp images. CONCLUSION: DECT at 80 kVp increases arterial enhancement in both CTPA and routine studies. For routine studies this results in central and peripheral enhancement quality equivalent to that of CTPA studies. Low tube-voltage imaging allows marked contrast volume reduction for CTPA. In selected cases, satisfactory lower radiation dose CT might be achievable using lower kVp imaging alone.