Ernst Klotz

Comparison of Perfusion Computed Tomography and Computed Tomography Angiography Source Images With Perfusion-Weighted Imaging and Diffusion-Weighted Imaging in Patients With Acute Stroke of Less Than 6 Hours’ Duration

Background and Purpose— We aimed to determine the diagnostic value of perfusion computed tomography (PCT) and CT angiography (CTA) including CTA source images (CTA-SI) in comparison with perfusion-weighted magnetic resonance imaging (MRI) (PWI) and diffusion-weighted MRI (DWI) in acute stroke <6 hours. Methods— Noncontrast-enhanced CT, PCT, CTA, stroke MRI, including PWI and DWI, and MR angiography (MRA), were performed in patients with symptoms of acute stroke lasting <6 hours. We analyzed ischemic lesion volumes on patients’ arrival as shown on NECT, PCT, CTA-SI, DWI, and PWI (Wilcoxon, Spearman, Bland–Altman) and compared them to the infarct extent as shown on day 5 NECT. Results— Twenty-two stroke patients underwent CT and MRI scanning within 6 hours. PCT time to peak (PCT-TTP) volumes did not differ from PWI-TTP (P =0.686 for patients who did not undergo thrombolysis/ P =0.328 for patients who underwent thrombolysis), nor did PCT cerebral blood volume (PCT-CBV) differ from PWI-CBV (P =0.893/ P =0.169). CTA-SI volumes did not differ from DWI volumes (P =0.465/ P =0.086). Lesion volumes measured in PCT maps significantly correlated with lesion volumes on PWI (P =0.0047, r =1.0/ P =0.0019, r =0.897 for TTP; P =0.0054, r =0.983/ P =0.0026, r =0.871 for CBV). Also, PCT-CBV lesion volumes significantly correlated with follow-up CT lesion volumes (P =0.0047, r =1.0/ P =0.0046, r =0.819). Conclusions— In hyperacute stroke, the combination of PCT and CTA can render important diagnostic information regarding the infarct extent and the perfusion deficit. Lesions on PCT-TTP and PCT-CBV do not differ from lesions on PWI-TTP and PWI-CBV; lesions on CTA source images do not differ from lesions on DWI. The combination of noncontrast-enhanced CT (NECT), perfusion CT (PCT), and CT angiography (CTA) can render additional information within <15 minutes and may help in therapeutic decision-making if PWI and DWI are not available or cannot be performed on specific patients.

Evaluation of a prototype dual-energy computed tomographic apparatus. I. Phantom studies.

We report the evaluation of a prototype dual-energy implementation using rapid kVp switching on a clinical computed tomographic scanner. The method employs prereconstruction basis material decomposition of the dual-energy projection data. Each dual-energy scan can be processed into conventional single-kVp images, basis material density images, and monoenergetic images. Phantom studies were carried out to qualitatively and quantitatively evaluate and validate the approach.

Quantitative Assessment of the Ischemic Brain by Means of Perfusion-Related Parameters Derived From Perfusion CT

Background and Purpose — Besides the delineation of hypoperfused brain tissue, the characterization of ischemia with respect to severity is of major clinical relevance, because the degree of hypoperfusion is the most critical factor in determining whether an ischemic lesion becomes an infarct or represents viable brain tissue. CT perfusion imaging yields a set of perfusion related parameters which might be useful to describe the hemodynamic status of the ischemic brain. Our objective was to determine whether measurements of the relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), and relative time to peak (rTP) can be used to differentiate areas undergoing infarction from reversible ischemic tissue. Methods — In 34 patients with acute hemispheric ischemic stroke <6 hours after onset, perfusion CT was used to calculate rCBF, rCBV, and rTP values from areas of ischemic cortical and subcortical gray matter. Results were obtained separately from areas of infarction and noninfarction, according to the findings on follow-up imaging studies. The efficiency of each parameter to predict tissue outcome was tested. Results — There was a significant difference between infarct and peri-infarct tissue for both rCBF and rCBV but not for rTP. Threshold values of 0.48 and 0.60 for rCBF and rCBV, respectively, were found to discriminate best between areas of infarction and noninfarction, with the efficiency of the rCBV being slightly superior to that of rCBF. The prediction of tissue outcome could not be increased by using a combination of various perfusion parameters. Conclusions — The assessment of cerebral ischemia by means of perfusion parameters derived from perfusion CT provides valuable information to predict tissue outcome. Quantitative analyses of the severity of ischemic lesions should be implemented into the diagnostic management of stroke patients.

Perfusion measurements of the brain: using dynamic CT for the quantitative assessment of cerebral ischemia in acute stroke.

OBJECTIVE Perfusion CT has been successfully used as a functional imaging technique for the differential diagnosis of patients with hyperacute stroke. We investigated to what extent this technique can also be used for the quantitative assessment of cerebral ischemia. METHODS AND MATERIAL We studied linearity, spatial resolution and noise behaviour of cerebral blood flow (CBF) determination with computer simulations and phantom measurements. Statistical ROI based analysis of CBF images of a subset of 38 patients from a controlled clinical stroke study with currently more than 75 patients was done to check the power of relative cerebral blood flow (rCBF) values to predict definite infarction and ischemic penumbra. Classification was performed using follow-up CT and MR data. RESULTS Absolute CBF values were systematically underestimated, the degree depended on the cardiac output of the patients. Phantom measurements and simulations indicated very good linearity allowing reliable calculation of rCBF values. Infarct and penumbra areas in 19 patients receiving standard heparin therapy had mean rCBF values of 0.19 and 0.62, respectively. The corresponding values for 19 patients receiving local intraarterial fibrinolysis were 0.18 and 0.57. The difference between infarct and penumbra values was highly significant (P < 0.0001) in both groups. No penumbra area was found with an rCBF value of less than 0.20. While in the heparin group only 25% of all areas with an rCBF between 0.20 and 0.35 survived, in the fibrinolytic group 61% of these areas could be saved (P < 0.05). CONCLUSION Perfusion CT is a fast and practical technique for routine clinical application. It provides substantial and important additional information for the selection of the optimal treatment strategy for patients with hyperacute stroke. Relative values of cerebral blood flow discriminate very well between areas of reversible and irreversible ischemia; an rCBF value of 0.20 appears to be a definite lower limit for brain tissue to survive an ischemic injury.

Stress and Rest Dynamic Myocardial Perfusion Imaging by Evaluation of Complete Time-Attenuation Curves With Dual-Source CT

OBJECTIVES This study sought to describe a protocol for myocardial perfusion imaging using dipyridamole stress, with 128-slice dual-source computed tomography (CT), and to assess the ability of CT myocardial perfusion imaging (MPI) to detect abnormal flow reserve and infarction in comparison with nuclear MPI (NMPI). BACKGROUND CT MPI has not been previously described with the 128-slice dual-source CT scanner, or with the complete evaluation of dynamic time-attenuation curves of the myocardium. METHODS Thirty-five patients underwent a stress CT MPI protocol. Complete time-attenuation curves of the myocardium were acquired using a novel scan mode, which acquires prospectively electrocardiogram (ECG)-triggered axial images at 2 rapidly alternating positions. Myocardial blood flow (MBF) values of fixed and reversible defects obtained were compared between rest and stress. Findings on CT MPI were correlated to NMPI. Perfusion defects detected on CT were correlated to coronary stenoses detected on CT angiography (CTA) and invasive coronary angiography (ICA). RESULTS There was a 1.5-fold difference between stress (1.21 +/- 0.31 cc/cc/min) and rest (0.82 +/- 0.22 cc/cc/min) MBF in normal tissue. In reversible defects, MBF was 0.65 +/- 0.21 cc/cc/min and 0.63 +/- 0.18 cc/cc/min at stress and rest, respectively. In fixed defects, the MBF was 0.57 +/- 0.22 cc/cc/min at stress and 0.54 +/- 0.23 cc/cc/min at rest. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of CT MPI for identifying segments with perfusion defects was 0.83, 0.78, 0.79, and 0.82, respectively. ICA results were available for 30 patients. Sensitivity, specificity, PPV, and NPV of CT MPI compared with ICA were 0.95, 0.65, 0.78, and 0.79, respectively. The radiation dose for CT MPI was 9.15 +/- 1.32 mSv for the stress scan and 9.09 +/- 1.40 mSv for the rest scan. CONCLUSIONS Vasodilator-stress CT MPI may be feasible in human subjects at a radiation dose similar to NMPI. It identifies areas of abnormal flow reserve and infarction with a high degree of correlation to NMPI as well as to stenoses detected in CTA and ICA.

Perfusion CT: Noninvasive Surrogate Marker for Stratification of Pancreatic Cancer Response to Concurrent Chemo- and Radiation Therapy

PURPOSE To prospectively determine whether perfusion computed tomography (CT) parameters, such as volume transfer constant (K(trans)) between blood plasma and extracellular extravascular space (EES) and blood volume calculated from dynamic CT data, can be used to predict response of pancreatic cancer to concurrent chemotherapy and radiation therapy (CCRT). MATERIALS AND METHODS This prospective study was institutional review board approved, and written informed consent was obtained. Thirty patients with pancreatic cancer underwent perfusion CT with 64-detector row CT before gemcitabine-based CCRT. Two perfusion parameters (K(trans) and blood volume) measured before treatment were compared between patients who responded to treatment and those who did not, as determined with World Health Organization criteria from first and second posttherapeutic follow-up CT examinations, which were performed at 3- and 6-month follow-up. Statistical analysis was performed with the two-sample t test. A receiver operating characteristic curve was used to determine the best cutoff value of perfusion parameters for differentiation of responders from nonresponders. RESULTS Twenty of 30 patients examined at 3-month follow-up responded to therapy. Their pretreatment K(trans) value was significantly higher than that of nonresponders (50.8 mL/100 mL/min +/- 30.5 [standard deviation] vs 19.0 mL/100 mL/min +/- 10.8, P = .001). The best cutoff value for differentiating between responders and nonresponders was 31.8 mL/100 mL/min, which yielded 75.0% sensitivity and 90.0% specificity. Ten of 18 patients examined at 6-month follow-up responded to therapy. Their pretreatment K(trans) value was significantly higher than that of nonresponders (58.6 mL/100 mL/min +/- 43.2 vs 19.8 mL/100 mL/min +/- 10.9, P = .002). Responders also had higher blood volume values, but this difference was not significant. CONCLUSION Tumors with a high pretreatment K(trans) value tended to respond better to CCRT than did tumors with a low pretreatment K(trans) value. Perfusion CT may be used to predict tumor response to CCRT in patients with pancreatic cancer. This might aid in development of a tailored approach to therapy in these patients.

Quantitative Whole Heart Stress Perfusion CT Imaging as Noninvasive Assessment of Hemodynamics in Coronary Artery Stenosis: Preliminary Animal Experience

Purpose:To quantify differences in regional myocardial perfusion in coronary artery stenosis by the use of dual source computed tomography (DSCT) in an animal model. Material and Methods:In 5 pigs, an 80% stenosis of the left anterior descending artery was successfully induced by partial balloon occlusion (ischemia group). Five animals served as control group. All animals underwent contrast enhanced whole heart DSCT (Definition Flash, Siemens, Germany) perfusion imaging using a prototype electrocardiogram -triggered dynamic scan mode. Imaging was performed at rest as well as under stress conditions during continuous infusion of adenosine (240 mg/kg/min). For contrast enhancement 60 mL Iopromide 300 (Ultravist 300, Bayer-Schering Pharma, Berlin, Germany) were injected at a rate of 6 mL/s. Myocardial blood flow (MBF), first pass distribution volume, and intravascular blood volume were volumetrically quantified. Results:In the control group MBF increased significantly from 98.2 mL/100 mL/min to 134.0 mL/100 mL/min if adenosine was administered (P = 0.0153). There were no significant differences in the perfusion parameters comparing the control and ischemia group at rest. In the ischemia group MBF under stress was 74.0 ± 21.9 mL/100 mL/min in the poststenotic myocardium and 117.4 ± 18.6 mL/100 mL/min in the remaining normal myocardium (P = 0.0024). Conclusion:DSCT permits quantitative whole heart perfusion imaging. As this technique is able to show the hemodynamic effect of high grade coronary artery stenosis, it exceeds the present key limitation of cardiac computed tomography, which currently only allows a morphologic assessment of coronary artery stenosis.

Stress Myocardial Perfusion: Imaging with Multidetector CT

Computed tomographic (CT) coronary angiography is a well-established, noninvasive imaging modality for detection of coronary stenosis, but it has limited accuracy in demonstrating whether a coronary stenosis is hemodynamically significant. An additional functional test is often required because both anatomic and functional information is needed for guiding patient care. Recent developments in CT technology allow CT evaluation of myocardial perfusion during vasodilator stress, thereby providing information about myocardial ischemia. Investigators in several single-center studies have established the feasibility of performing stress myocardial perfusion CT imaging in small groups of patients and have shown that stress myocardial perfusion CT in combination with CT coronary angiography improved the diagnostic accuracy in comparison with CT coronary angiography alone. However, CT perfusion acquisition protocols must be optimized in terms of acquisition and reconstruction parameters, contrast material protocol injections, and radiation dose. Further research is needed to establish the clinical usefulness of this novel technique. The purpose of this review is to (a) provide an overview of the physiology of coronary circulation and myocardial perfusion; (b) describe the technical prerequisites, challenges, and mathematic modeling related to CT perfusion imaging; (c) note recent advances in CT scanners and CT perfusion protocols; and (d) discuss the interpretation of CT perfusion images. Finally, a review and summary of the current literature are provided, and future directions for research are discussed.

Multidetector-row computed tomography of the coronary arteries: predictive value and quantitative assessment of non-calcified vessel-wall changes

The aim of this study was to quantitatively assess non-calcified coronary artery plaques and to determine their predictive value for the detection of coronary artery disease (CAD). A total of 179 patients underwent a calcium screening examination and a contrast-enhanced multidetector-row computed tomography angiography (MDCT) of the coronary arteries for various indications. The traditional calcium scores were evaluated and all examinations were reviewed for the presence of non-calcified plaques with an attenuation of 0–130 Hounsfield units (HU). The number, mean attenuation, and volume of these non-calcified plaques were recorded. All patients also underwent conventional catheter angiography. Coronary calcium was detected in 73% (131 of 179) of the patients. Overall incidence of purely non-calcified plaques was 30% (53 of 179). In 27% of the patients (48 of 179) no calcium was detected; however, 15% of these patients without calcifications showed non-calcified plaques (7 of 48). Significant correlations were found between the volume of calcified plaques, volume of non-calcified plaques, and total plaque volume. There were significant differences in plaque composition comparing different risk factor profiles and different stages of CAD. Volumetric assessment of non-calcified coronary artery plaques is feasible using contrast-enhanced MDCT. Screening for non-calcified plaques identifies patients with signs of CAD that are missed in a calcium screening examination.

MOSAIC: Multimodal Stroke Assessment Using Computed Tomography Novel Diagnostic Approach for the Prediction of Infarction Size and Clinical Outcome

Background and Purpose— With new CT technologies, including CT angiography (CTA), perfusion CT (PCT), and multidetector row technique, this method has regained interest for use in acute stroke assessment. We have developed a score system based on Multimodal Stroke Assessment Using CT (MOSAIC), which was evaluated in this prospective study. Methods— Forty-four acute stroke patients (mean age, 63.8 years) were enrolled within a mean of 3.0±1.9 hours after symptom onset. The MOSAIC score (0 to 8 points) was generated by results of the 3 sequential CT investigations: (1) presence and amount of early signs of infarction on noncontrast CT (NCCT; 0 to 2 points), (2) stenosis (>50%) or occlusion of the distal internal carotid or middle cerebral artery on CTA (0 to 2 points), and (3) presence and amount of reduced cerebral blood flow on 2 adjacent PCT slices (0 to 4 points). The predictive value of the MOSAIC score was compared with each single CT component with respect to the final size of infarction and the clinical outcome 3 months after stroke by use of the modified Rankin Scale (mRS) and the Barthel Index (BI). Results— Among the CT components, PCT showed the best correlation to infarction size (r =0.75) and clinical outcome (r =0.60 to 0.62) compared with NCCT (r =0.43 to 0.58) and CTA (r =0.47 to 0.71). The MOSAIC score showed consistently higher correlation factors (r =0.67 to 0.78) and higher predictive values (0.73 to 1.0) than all single CT components with respect to outcome measures. A MOSAIC score <4 predicted independence with 89% to 96% likelihood (mRS ≤2, BI ≥90); a MOSAIC score <5 predicted fair outcome with 96% to 100% likelihood (mRS ≤3, BI ≥60). Conclusions— The MOSAIC score based on multidetector row CT technology is superior to NCCT, CTA, and PCT in predicting infarction size and clinical outcome in hyperacute stroke.