Robert Goetti

Low-dose, 128-slice, dual-source CT coronary angiography: accuracy and radiation dose of the high-pitch and the step-and-shoot mode

Objective To compare the diagnostic accuracy and radiation doses of two low-dose protocols for coronary artery imaging with second-generation, dual-source CT in comparison with catheter angiography (CA). Design, setting and patients Prospective, single-centre study conducted in a referral centre enrolling 100 patients with low-to-intermediate risk and suspicion of coronary artery disease. All patients underwent contrast-enhanced, 128-slice, dual-source CT coronary angiography and CA. Patients were randomly assigned to two different low-dose CT protocols (each 100 kV/320 mA): in group A (n=50), CT was performed using the prospectively electrocardiography (ECG)-gated step-and-shoot (SAS) mode; in group B (n=50), CT was performed using the prospectively ECG-gated high-pitch mode (pitch 3.4). The image quality and presence or absence of significant coronary stenosis in all coronary segments were evaluated by two blinded and independent observers. CA served as the standard of reference. Results Sixty-one significant stenoses were found in group A, and 69 in group B. There was no significant difference in age (group A, 62±8yrs; group B, 63±8yrs; p=0.72), body mass index (group A, 26.4±3.1kg/m2; group B, 25.9±2.8kg/m2; p=0.41) and heart rate (HR) (group A, 58±8bpm; group B, 56±10bpm; p=0.66) between the groups. Diagnostic image quality was obtained in 98.6% (651/660) of segments in group A and in 98.9% (642/649) in group B, with no significant differences between groups. Sensitivity, specificity and positive and negative predictive values were 94%, 91%, 85% and 97% per-patient in group A, and 93%, 94%, 89% and 97% per-patient in group B (no significant differences). The effective radiation dose in group B (0.9±0.1 mSv) was significantly (p<0.01) lower than that in group A (1.4±0.4 mSv). Conclusions Both the high-pitch and the SAS mode for low-dose CT coronary angiography provide high accuracy for the assessment of significant coronary stenoses, while the high-pitch mode further significantly lowers the radiation dose.

Automated attenuation-based tube potential selection for thoracoabdominal computed tomography angiography: improved dose effectiveness.

Purpose:To introduce a novel algorithm of automated attenuation-based tube potential selection and to assess its impact on image quality and radiation dose of body computed tomography angiography (CTA). Materials and Methods:In all, 40 patients (mean age 71 ± 11.8 years, body mass index (BMI) 25.7 ± 3.8 kg/m2, range 18.8–33.8 kg/m2) underwent 64-slice thoracoabdominal CTA (contrast material: 80 mL, 5 mL/s) using an automated tube potential selection algorithm (CAREkV), which optimizes tube-potential (70–140 kV) and tube-current (138.8 ± 18.6 effective mAs, range 106–177 mAs) based on the attenuation profile of the topogram and on the diagnostic task. Image quality was semiquantitatively assessed by 2 blinded and independent readers (scores 1: excellent to 5: nondiagnostic). Attenuation and noise were measured by another 2 blinded and independent readers. Contrast-to-noise ratio was calculated. The CT dose index (CTDIvol) was recorded and compared with the estimated CTDIvol of a standard 120 kV protocol without using the algorithm in each patient. Selected tube potentials were correlated with BMI and attenuation of the topogram. Results:Diagnostic image quality was obtained in all patients (excellent: 14; good: 21; moderate: 5; interreader agreement: &kgr; = 0.78). Mean attenuation, noise, and contrast-to-noise ratio were 260.8 ± 63.5 Hounsfield units, 15.5 ± 3.3 Hounsfield units, and 14 ± 4.2, respectively, with good to excellent agreement between readers (r = 0.50–0.99, P < 0.01 each). Automated attenuation-based tube potential selection resulted in a kV-reduction from 120 to 100 kV in 23 patients and to 80 kV in 1 patient, whereas tube potential increased to 140 kV in 1 patient. Automatically selected tube potential showed a significant correlation with both BMI (r = 0.427, P < 0.05) and attenuation of the topogram (r = 0.831, P < 0.001). CTDIvol (7.95 ± 2.6 mGy) was significantly lower when using the algorithm compared with the standard 120 kV protocol (10.59 ± 1.8 mGy, P < 0.001), corresponding to an overall dose reduction of 25.1%. Conclusion:Automated attenuation-based tube potential selection based on the attenuation profile of the topogram is feasible, provides a diagnostic image quality of body CTA, and reduces overall radiation dose by 25% as compared with a standard protocol with 120 kV.

Adenosine stress high-pitch 128-slice dual-source myocardial computed tomography perfusion for imaging of reversible myocardial ischemia: comparison with magnetic resonance imaging.

Background— Coronary computed tomography angiography (CTA) enables accurate anatomic evaluation of coronary artery stenosis but lacks information about hemodynamic significance. The aim of this study was to evaluate 128-slice myocardial CT perfusion (CTP) imaging with adenosine stress using a high-pitch mode, in comparison with cardiac MRI (CMR). Methods and Results— Thirty-nine patients with intermediate to high coronary risk profile underwent adenosine stress 128-slice dual source CTP (128×0.6 mm, 0.28 seconds). Among those, 30 patients (64±10 years, 6% women) also underwent adenosine stress CMR (1.5T). The 2-step CTP protocol consisted of (1) adenosine stress-CTP using a high-pitch factor (3.4) ECG-synchronized spiral mode and (2) rest-CTP/coronary-CTA using either high-pitch (heart rate <63 bpm) or prospective ECG-triggering (heart rate >63 bpm). Results were compared with CMR and with invasive angiography in 25 patients. The performance of stress-CTP for detection of myocardial perfusion defects compared with CMR was sensitivity, 96%; specificity, 88%; positive predictive value (PPV), 93%; negative predictive value (NPV), 94% (per vessel); and sensitivity, 78%; specificity, 87%; PPV, 83%; NPV, 84% (per segment). The accuracy of stress-CTP for imaging of reversible ischemia compared with CMR was sensitivity, 95%; specificity, 96%; PPV, 95%; and NPV, 96% (per vessel). In 25 patients who underwent invasive angiography, the accuracy of CTA for detection of stenosis >70% was (per segment): sensitivity, 96%; specificity, 88%; PPV, 67%; and NPV, 98.9%. The accuracy improved from 84% to 95% after adding stress CTP to CTA. Radiation exposure of the entire stress/rest CT protocol was only 2.5 mSv. Conclusions— Adenosine-induced stress 128-slice dual-source high-pitch myocardial CTP allows for simultaneously assessment of reversible myocardial ischemia and coronary stenosis, with good diagnostic accuracy as compared with CMR and invasive angiography, at a very low radiation exposure.

High-Pitch Dual-Source CT Angiography of the Thoracic and Abdominal Aorta: Is Simultaneous Coronary Artery Assessment Possible?

OBJECTIVE The purpose of this study was to prospectively evaluate the average heart rate and heart rate variability required for diagnostic imaging of the coronary arteries with high-pitch dual-source CT angiography of the thoracic and thoracoabdominal aorta. SUBJECTS AND METHODS One hundred consecutively registered patients (82 men, 18 women; mean age, 68 +/- 13 years) underwent clinically indicated CT angiography of the thoracic (n = 33) and thoracoabdominal (n = 67) aorta with a dual-source 128-MDCT scanner in ECG-synchronized high-pitch (pitch, 3.2) data acquisition mode. No beta-blockers were administered. The image quality of the coronary arteries was graded on a 3-point scale by two independent blinded readers. The average heart rate and heart rate variability before data acquisition were noted. Effective radiation doses were calculated. RESULTS Interobserver agreement on grade of image quality for the 1,414 coronary segments evaluated by both observers was good (kappa = 0.68). Diagnostic image quality was found for 1,375 of the 1,414 segments (97.2%) in 83 of 100 patients (83%). In 17% of the patients, image quality was nondiagnostic for at least one coronary artery segment. Average heart rate and heart rate variability (each p < 0.05) were significantly higher in patients with at least one nondiagnostic coronary segment compared with those without. All patients with an average heart rate less than 63 beats/min and heart rate variability less than 1.2 beats/min had diagnostic image quality in all coronary segments. Effective radiation doses were 2.3 +/- 0.3 mSv for thoracic and 4.4 +/- 0.5 mSv for thoracoabdominal CT angiography. The average scan times were 0.88 +/- 0.06 second for thoracic and 1.67 +/- 0.15 seconds for thoracoabdominal CT angiography. CONCLUSION For patients with an average heart rate less than 63 beats/min and heart rate variability less than 1.2 beats/min, dual-source CT angiography of the thoracoabdominal aorta at a high pitch of 3.2 delivers diagnostic depiction of the coronary arteries at a low radiation dose.

Quantitative computed tomography liver perfusion imaging using dynamic spiral scanning with variable pitch: feasibility and initial results in patients with cancer metastases.

Purpose:To assess the feasibility and image quality of computed tomography (CT) liver perfusion imaging using an adaptive 4D spiral-mode, developed to extend the z-axis coverage, and to report initial qualitative and quantitative results in patients with cancer metastases. Materials and Methods:A total of 21 patients with liver metastases of various origins underwent CT perfusion imaging (100 kV and 150 mAs/rot) using a 4D spiral-mode with single-source 64-slice CT (n = 7) with a scan range of 6.7cm (protocol A: 16 cycles, 46.5 seconds examination time), or dual-source 128-slice CT with a scan range of 14.8 cm (protocol B: 16 cycles, 46.5 seconds examination time, n = 7; protocol C: 12 cycles, 51.0 seconds examination time, n = 7). Ability to suspend respiration during perfusion imaging was monitored. Two independent readers assessed image quality on a 4-point scale, both before and after motion correction, and performed a qualitative (ie, arterial enhancement pattern and enhancement change over time) and quantitative perfusion (ie, arterial liver perfusion [ALP]; portal-venous perfusion [PVP]; hepatic perfusion index [HPI]) analysis. Results:Of 21 patients, 7 (33%) could suspend respiration throughout the perfusion study and 14 (67%) resumed shallow breathing during the perfusion scan. The 21 patients had a total of 88 metastases. The scan range of protocol A covered at least 1 metastasis in all patients (total 20/34 [58.8%] metastases). The scan range of protocol B and C covered 53 of 54 (98.1%) metastases, whereas one metastasis in segment VIII was only partially imaged. Image quality was diagnostic both before and after motion correction, whereas being significantly better after motion correction (P < 0.001). Qualitative perfusion analysis of 67 metastases revealed diffuse arterial enhancement in 3 (4.5%), sparse enhancement in 11 (16.4%), peripheral-nodular enhancement in 9 (13.4%), rim-like enhancement in 15 (22.4%), and none in 29 (43.3%) metastases. Enhancement over time of 67 metastases showed a centripetal progression in 6 (8.9%), sustained portal phase in 16 (23.9%), wash-out in 16 (23.9%), and none in 29 (43.3%) metastases. Quantitative perfusion analysis revealed significantly higher arterial liver perfusion and HPI in metastases and metastasis borders than in adjacent normal liver tissue (P < 0.001 each). Portal-venous perfusion was significantly lower in metastases and metastasis borders than in normal liver tissue (P < 0.001). There were no significant differences in image quality and qualitative perfusion analysis between the 3 protocols (P = n.s.). Calculated effective radiation doses were 13.4 mSv for protocol A, 30.7 mSv for protocol B, and 23.0 mSv for protocol C. Conclusion:CT perfusion imaging of the liver using the 4D spiral-mode is feasible with diagnostic image quality, and enables the reliable qualitative and quantitative analysis of the normal and metastatic liver parenchyma. Radiation dose issues must be considered when determining the scan range, number of cycles, and scan duration of the perfusion CT protocol.

Impact of cardiac hybrid single-photon emission computed tomography/computed tomography imaging on choice of treatment strategy in coronary artery disease

Aims Cardiac hybrid imaging by fusing single-photon emission computed tomography (SPECT) myocardial perfusion imaging with coronary computed tomography angiography (CCTA) provides important complementary diagnostic information for coronary artery disease (CAD) assessment. We aimed at assessing the impact of cardiac hybrid imaging on the choice of treatment strategy selection for CAD. Methods and results Three hundred and eighteen consecutive patients underwent a 1 day stress/rest 99mTc-tetrofosmin SPECT and a CCTA on a separate scanner for evaluation of CAD. Patients were divided into one of the following three groups according to findings in the hybrid images obtained by fusing SPECT and CCTA: (i) matched finding of stenosis by CCTA and corresponding reversible SPECT defect; (ii) unmatched CCTA and SPECT finding; (iii) normal finding by both CCTA and SPECT. Follow-up was confined to the first 60 days after hybrid imaging as this allows best to assess treatment strategy decisions including the revascularization procedure triggered by its findings. Hybrid images revealed matched, unmatched, and normal findings in 51, 74, and 193 patients. The revascularization rate within 60 days was 41, 11, and 0% for matched, unmatched, and normal findings, respectively (P< 0.001 for all inter-group comparisons). Conclusion Cardiac hybrid imaging with SPECT and CCTA provides an added clinical value for decision making with regard to treatment strategy for CAD.

Dual-energy CT for characterization of the incidental adrenal mass: preliminary observations.

OBJECTIVE The purpose of our study was to evaluate the accuracy of virtual unenhanced images reconstructed from contrast-enhanced dual-energy CT for the differentiation of incidental adrenal masses in comparison with standard unenhanced CT. MATERIALS AND METHODS One hundred-forty patients (mean age, 74±9 years) underwent unenhanced and contrast-enhanced CT of the abdomen, the latter acquired with dual-energy for reconstruction of virtual unenhanced images. Two blinded and independent readers (R1 and R2) measured attenuation of each incidental adrenal mass on standard unenhanced and virtual unenhanced images using an optimized dual-energy three-material decomposition algorithm. RESULTS Fifty-one incidental adrenal masses were found in 42 of 135 patients (31%); 39 incidental adrenal masses were ≥1 cm. On the basis of unenhanced CT, 29 of 51 incidental adrenal masses and 22 of 39 incidental adrenal masses≥1 cm were classified as benign (HU<10). Virtual unenhanced image quality was rated as good or with mild impairment (2.45±0.83 for R1, 2.45±0.99 for R2). Image noise was 12.7±3.6 HU in unenhanced images and 8.8±2.0 HU in virtual unenhanced images (p<0.001). There was no significant difference in incidental adrenal mass attenuation between unenhanced and virtual unenhanced images for all incidental adrenal masses (5.9±21.0 HU vs 7.0±20.6 HU, p=0.48) and for those≥1 cm (6.6±18.5 HU vs 7.9±18.3 HU, p=0.87). Sensitivity, specificity, and accuracy of virtual unenhanced images for the characterization of incidental adrenal masses as probably benign were 76%, 82%, and 78% for R1 and 79%, 95%, and 86% for R2, respectively. For incidental adrenal masses≥1 cm, sensitivity, specificity, and accuracy increased to 95%, 100%, and 97% for R1 and 91%, 100%, and 95% for R2. CONCLUSION Reconstruction of virtual unenhanced images from contrast-enhanced dual-energy CT of the abdomen allows the characterization of the incidental adrenal masses with a good accuracy compared with standard unenhanced CT, with the most favorable results in incidental adrenal masses measuring≥1 cm.

Quantification of liver fat in the presence of iron and iodine: an ex-vivo dual-energy CT study.

Purpose:Iodinated contrast media (CM) and iron in the liver are known to hinder an accurate quantification of liver fat content (LFC) with single-energy computed tomography (SECT). The purpose of this study was to evaluate the feasibility and accuracy of dual-energy CT (DECT) for ex vivo quantification of LFC, in the presence of iron and CM, compared with SECT. Materials and Methods:Sixteen phantoms with a defined LFC of 0%, 10%, 30%, and 50% fat and with varying iron content (0, 1.5, 3, and 6 mg/mL wet weight liver) were scanned with a second-generation dual-source 128-slice CT system. Phantoms were scanned unenhanced and contrast-enhanced after adding 1.0 mg/mL iodine to each phantom. Both SECT (120 kV) and DECT (tube A: 140 kV, using a tin filter 228 mAs; tube B: 80 kV, 421 mAs) data were acquired. An iron-specific dual-energy 3-material decomposition algorithm providing virtual noniron images (VNI) was used to subtract iron and CM from the data. CT numbers (Hounsfield units) were measured in all data sets, including 120 kV from SECT, as well as 140 kV, 80 kV, 50%:50% weighted 80 kV/140 kV, and VNI derived from DECT. The dual-energy index was calculated from 80 kV and 140 kV data. SECT and DECT measurements (Hounsfield units) including the dual-energy index of unenhanced and contrast-enhanced phantoms were compared with the known titrated LFC, using Pearson correlation analysis and Student t test for related samples. Results:Inter-reader agreement was excellent for all measurements of CT numbers in both SECT and DECT data (Pearson r, 0.965–1.0). For fat quantification in the absence of iron and CM, CT numbers were similar in SECT and DECT (all, P > 0.05), showing a linear correlation with titrated LFC (r ranging from 0.981 to 0.999; P < 0.01). For fat quantification in the presence of iron but without CM, significant underestimation of LFC was observed for all measurements in SECT and DECT (P < 0.05), except for VNI. Measurements in VNI images allowed for an accurate LFC estimation, with no significant differences compared with measurements in iron-free phantoms (all, P > 0.25). For fat quantification in the presence of iron and CM, further underestimation of LFC was seen for measurements in SECT and DECT (P < 0.015), except for VNI. Measurements in VNI images showed a high accuracy for estimating the LFC, with no significant difference compared with measurements in iron- and CM-free phantoms (P > 0.2). Conclusions:Our ex vivo phantom study indicates that DECT with the use of a dedicated, iron-specific 3-material decomposition algorithm allows for the accurate quantification of LFC, even in the presence of iron and iodinated CM. VNI images reconstructed from DECT data equal nonenhanced SECT data of liver without CM by eliminating iron and iodine from the images. No added value was seen for DECT as compared with SECT for quantification of LFC in the absence of iron and iodine.

Very high coronary calcium score unmasks obstructive coronary artery disease in patients with normal SPECT MPI.

Objectives To study the clinical impact of a very high coronary artery calcium score (CAC >1000) in patients with no known coronary artery disease (CAD) and normal single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI). The secondary aim was to evaluate whether triple vessel disease would support the notion of balanced ischaemia as an underlying mechanism of false negative SPECT MPI in patients with very high CAC. Background No data exist on the clinical value of high CAC in patients with normal SPECT MPI. Methods 50 patients with suspected CAD and normal stress/rest SPECT MPI and CAC >1000 prospectively underwent invasive coronary angiography as the standard of reference. Coronary lesions with ≥50% luminal diameter narrowing on invasive coronary angiography were considered to represent significant stenosis. Results The median total CAC was 1975 (range 1018–8046). In 37/50 (74%) patients, coronary angiography revealed one-vessel disease (1-VD) (n=15), 2-VD (n=10) or 3-VD (n=12). Twenty-six revascularisations (percutaneous coronary intervention/coronary artery bypass grafting) were performed in seven (6/1), seven (6/1) and 12 (7/5) patients with 1-VD, 2-VD and 3-VD, respectively. Conclusions In patients with normal SPECT MPI, a CAC >1000 confers a high diagnostic added value for detecting CAD. This is not solely based on unmasking balanced ischaemia due to epicardial 3-VD, as it occurred predominantly in patients with 1-VD and 2-VD.

Prospective and retrospective ECG-gating for CT coronary angiography perform similarly accurate at low heart rates

OBJECTIVE To compare, in patients with suspicion of coronary artery disease (CAD) and low heart rates, image quality, diagnostic performance, and radiation dose values of prospectively and retrospectively electrocardiography (ECG)-gated dual-source computed tomography coronary angiography (CTCA) for the diagnosis of significant coronary stenoses. MATERIALS AND METHODS Two-hundred consecutive patients with heart rates ≤70 bpm were retrospectively enrolled; 100 patients undergoing prospectively ECG-gated CTCA (group 1) and 100 patients undergoing retrospectively-gated CTCA (group 2). Coronary artery segments were assessed for image quality and significant luminal diameter narrowing. Sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and accuracy of both CTCA groups were determined using conventional catheter angiography (CCA) as reference standard. Radiation dose values were calculated. RESULTS Both groups were comparable regarding gender, body weight, cardiovascular risk profile, severity of CAD, mean heart rate, heart rate variability, and Agatston score (all p>0.05). There was no significant difference in the rate of non-assessable coronary segments between group 1 (1.6%, 24/1404) and group 2 (1.4%, 19/1385; p=0.77); non-diagnostic image quality was significantly (p<0.001) more often attributed to stair step artifacts in group 1. Segment-based sensitivity, specificity, PPV, NPV, and accuracy were 98%, 98%, 88%, 100%, and 100% among group 1; 96%, 99%, 90%, 100%, and 98% among group 2, respectively. Parameters of diagnostic performance were similar (all p>0.05). Mean effective radiation dose of prospectively ECG-gated CTCA (2.2±0.4 mSv) was significantly (p<0.0001) smaller than that of retrospectively ECG-gated CTCA (8.1±0.6 mSv). CONCLUSION Prospectively ECG-gated CTCA yields similar image quality, performs as accurately as retrospectively ECG-gated CTCA in patients having heart rates ≤70 bpm while being associated with a lower mean effective radiation dose.