Hans-Jürgen Kaiser

Strain rate measurement by Doppler echocardiography allows improved assessment of myocardial viability in patients with depressed left ventricular function

OBJECTIVES This study sought to evaluate whether objective assessment of the myocardial functional reserve, using strain rate imaging (SRI), allows accurate detection of viable myocardium. BACKGROUND Strain rate imaging is a new echocardiographic modality that allows quantitative assessment of segmental myocardial contractility. METHODS In 37 patients (age 58 +/- 9 years) with ischemic left ventricular dysfunction, myocardial viability was assessed using low-dose (10 microg/kg body weight per min) two-dimensional dobutamine stress echocardiography (DSE), tissue Doppler imaging, SRI and (18)F-fluorodeoxyglucose ((18)FDG) positron emission tomography (PET). The peak systolic tissue Doppler velocity and peak systolic myocardial strain rate were determined at baseline and during low-dose dobutamine stress from the apical views. RESULTS A total of 192 segments with dyssynergy at rest were classified by (18)FDG PET as viable in 94 and nonviable in 98. An increase of peak systolic strain rate from rest to dobutamine stimulation by more than -0.23 1/s allowed accurate discrimination of viable from nonviable myocardium, as determined by (18)FDG PET with a sensitivity of 83% and a specificity of 84%. Receiver operating characteristic (ROC) curve analysis showed an area under the curve for prediction of nonviable myocardium, as determined by (18)FDG PET using SRI, of 0.89 (95% confidence interval [CI] 0.88 to 0.90), whereas the area under the ROC curve using tissue Doppler imaging was 0.63 (95% CI 0.61 to 0.65). CONCLUSIONS The increase in the peak systolic strain rate during low-dose dobutamine stimulation allows accurate discrimination between different myocardial viability states. Strain rate imaging is superior to two-dimensional DSE and tissue Doppler imaging for the assessment of myocardial viability.

MRI for attenuation correction in PET: methods and challenges

In current combined PET/MR systems, PET attenuation correction is based on MRI, since the small bore inside MRI systems and the strong magnetic field do not permit a rotating PET transmission source or a CT device to be integrated. Unlike CT measurements in PET/CT scanners, the MR signal is not directly correlated to tissue density and thus cannot be converted by a simple transformation of intensity values. Various approaches have been developed based on templates, atlas information, direct segmentation of T1-weighted MR images, or segmentation of images from special MR sequences. The advantages and disadvantages of these approaches as well as additional challenges will be discussed in this review.

Fluorine-18 deoxyglucose PET for assessment of viable myocardium in perfusion defects in 99mTc-MIBI SPET: a comparative study in patients with coronary artery disease*

Extent and frequency of viable tissue in myocardial segments yielding a perfusion defect on technetium-99m methoxyisobutylisonitrile (99mTc-MIBI), single photon emission tomography (SPET) at rest was prospectively investigated with 2-18F-2-deoxyglucose (18FDG) positron emission tomography (PET) in 46 patients with chronic coronary artery disease (CAD). Of these, 43 had a history of old myocardial infarction. For comparative visual and quantitative evaluation of identical anatomical slices, PET image files were converted into the SPET file structure and into the same matrix size. SPET and PET images were documented and visually (9 segments/patient) or semiquantitatively evaluated by a target-like polar map. Relative perfusion was expressed in percentage of peak 99mTc-MIBI uptake. Sample 18FDG uptake was related to the 18FDG uptake in the area of such maximal perfusion (18FDG uptake was 100% at the 100% 99mTc-MIBI uptake area). Of 414 segments, 167 (40%) revealed a resting perfusion defect. 18FDG uptake was present in 38 (23%) of the defects, while another 40 (24%) segments yielded 18FDG uptake in the periphery of the defect. When grouped according to the degree of 99mTc-MIBI uptake-reduction (in percentage of peak activity), 80% of severe defects (≤30% of peak uptake), 48% of moderate (31%–50% of peak uptake) and 31% of mild (>50% of peak uptake) defects were considered as non-viable on the basis of 18FDG uptake. Complete viability was found in none of the severe defects in contrast to 29% of moderate and 35% of mild perfusion defects. From these data we conclude that 99mTc-MIBI uptake as a myocardial perfusion marker underestimates myocardial viability in patients with chronic CAD and after myocardial infarction. Nevertheless, only moderate reductions of 99mTc-MIBI uptake seem to imply a greater likelihood for viability. Comparative analysis of metabolism and flow is possible with different tomographic systems and is valuable for clinical evaluation of the cardiac patient.

Dual-head gamma camera 2-[fluorine-18]-fluoro-2-deoxy-d-glucose positron emission tomography in oncological patients: effects of non-uniform attenuation correction on lesion detection

Abstract. The purpose of this study was to evaluate a dual head coincidence gamma camera (DH-PET) equipped with single-photon transmission for 2-[fluorine-18]-fluoro-2-deoxy-d-glucose (FDG) imaging in oncological patients. Forty-five patients with known or suspected malignancies, scheduled for a positron emission tomography (PET) scan, were first studied with a dedicated ring PET and subsequently with DH-PET. All patients underwent measured attenuation correction using germanium-68 rod sources for ring PET and caesium-137 sources for DH-PET. Ring PET emission scan was started 64±17 min after intravenous administration of 235±42 MBq FDG. DH-PET emission followed 160±32 min after i.v. FDG. Attenuation-corrected and non-attenuation-corrected images were reconstructed for ring PET and DH-PET. The image sets were evaluated independently by three observers blinded to clinical data and to results of conventional imaging. Attenuation-corrected ring PET as the standard of reference depicted 118 lesions, non-attenuation-corrected ring PET 113 (96%) lesions, and attenuation-corrected DH-PET and non-attenuation-corrected DH-PET, 101 (86%) and 84 (71%) lesions, respectively (P<0.05). The lesion detection rate of attenuation-corrected and non-attenuation-corrected DH-PET was almost similar for lesions >20 mm, whereas attenuation correction increased the detection rate from 60% to 80% for lesions ≤20 mm (P<0.01). A patient-based analysis revealed concordant results relative to attenuation-corrected ring PET for non-attenuation-corrected ring PET, attenuation-corrected DH-PET and non-attenuation-corrected DH-PET in 42 (93%), 36 (80%) and 31 (69%) patients, respectively. Differences might have influenced patient management in two (4%), six (13%) and ten (22%) patients, respectively. In conclusion, measured attenuation correction markedly improves the lesion detection capability of DH-PET. With measured attenuation correction the diagnostic performance of DH-PET is closer to that of dedicated ring PET.

Hybrid Spline-Based Multimodal Registration Using Local Measures for Joint Entropy and Mutual Information

We introduce a new hybrid approach for spline-based elastic registration of multimodal medical images. The approach uses point landmarks as well as intensity information based on local analytic measures for joint entropy and mutual information. The information-theoretic similarity measures are computationally efficient and can be optimized independently for each voxel. We have applied our approach to synthetic images, brain phantom images, as well as clinically relevant multimodal medical images. We also compared our measures with previous measures.

Methoxyisobutylisonitrile (MIBI) Tc 99m SPECT to establish a correlate to coronary flow reserve, the perfusion reserve, from global and regional myocardial uptake after exercise and rest

With99mTc-MIBI SPECT and a 4 h exercise (E; 150 MBq iv) and rest (R; 800 MBq iv) protocol global and regional left ventricular (LV) myocardial uptake was determined in 70 patients with angiographicall, confirmed coronary heart disease (CHD) and in 10 controls. The aim was to establish an E/R ratio as a correlate to coronary vascular reserve, representing perfusion reserve (PR). E/R ratios, obtained from total LV myocardium or from normal or impaired regions, were > 1.19 under all conditions, indicating the presence of higher flow during exercise than at rest (even in areas of low flow). Global PR separated (P<0.01) controls (1.63±0.21; mean ± SD) from severely diseased patients (1.29 ±0.14 in 2- or 3-vessel disease) only. Improved differential diagnosis was gained from calibrating the regional E/R ratio to regional differences (E minus R) of uptake. For the left ventricle regional PRs (RPR) for 25 ROIs of the target, framing the myocardium, were determined RPR at the regional maximum of99mTc-MIBI uptake was similar in both controls (1.66) and patients (1.63), indicating a high probability of meeting some areas with functionally normal perfusion in patients with CHD. RPR allowed sufficient separation (P<0.025) concerning the degree of coronary artery stenosis (RPR in occlusion, 0.26; stenosis >75%, 0.39; <75%, 0.56). In controls, the overall value for RPR was 1.14+0.28 (P< 0.001). LV global PR and RPR were useful in separating patients with CHD vs controls and in classifying the severity of vascular stenosis.

Pulsed Tissue Doppler Imaging to Assess Myocardial Viability by Quantification of Regional Myocardial Functional Reserve

Dobutamine stress echocardiography (DSE) is used widely to evaluate myocardial viability, but is limited by the subjective nature of test interpretation. Assessment of systolic function by pulsed tissue Doppler imaging (TDI) during dobutamine stimulation may allow a more objective evaluation of myocardial functional reserve and, thus, myocardial viability. In 30 patients (58 ± 9 years) with prior myocardial infarction, pulsed TDI with low dose dobutamine stress (10 μg/kg/min) was performed to assess myocardial viability. Qualitative assessment of two‐dimensional (2‐D) DSE and positron emission tomography (PET) were used for comparison. Peak systolic myocardial velocity was measured for each left ventricular segment (16 segments) at baseline and low dose dobutamine stress using pulsed TDI. The absolute and relative increases of peak systolic velocity from rest to low dose dobutamine stress were calculated. Three hundred sixty‐four segments with adequate pulsed TDI tracing were divided according to either 2‐D DSE or PET findings into normal, viable (mismatch), and nonviable (match) segments. The increase of peak systolic myocardial velocity from baseline to low dose dobutamine was significantly different between segments defined as normal, viable, and nonviable by 2‐D DSE (2.71 ± 1.91 cm/sec, 1.86 ± 2.15 cm/sec, and 0.99 ± 1.16 cm/sec, respectively; P < 0.001). The increase of peak systolic myocardial velocity from rest to low dose dobutamine for normal, mismatch, and match segments defined by PET was 2.72 ±1.96, 1.01 ± 0.96 and 0.80 ± 1.07 cm/sec, respectively (P < 0.001). In conclusion, the increase of peak systolic myocardial velocity during low dose dobutamine stimulation determined by pulsed TDI distinguishes between different myocardial viability states. It complements the standard interpretation of stress echocardiograms.

MRT-basierte individuelle Regionenatlanten des menschlichen Gehirns Ziele, Methoden, Ausblick

Die direkte automatisierte Generierung dreidimensionaler Regionenatlanten des menschlichen Gehirns auf der Basis von individuellem kernspintomographischen Bilddatenmaterial (MRTBilddaten) berucksichtigt die interindividuelle Variabilitat menschlicher Gehirne. Die hierzu entwickelte Methodik besteht aus zwei aufeinander aufbauenden Schritten: der Gewebeklassifikation („Low Level“-Verarbeitung) und der wissensbasierten Analyse zur Extraktion anatomischer Regionen („High Level“-Verarbeitung). Die Quantifizierung koregistrierter emissionscomputertomographischer Bilddaten (ECT-Bilddaten) auf Basis der zugehorigen individuellen Atlanten ermoglicht die Berucksichtigung partialvolumenbedingter Effekte.

Hybrid Spline-Based Multimodal Registration Using a Local Measure for Mutual Information

We introduce a new hybrid approach for spline-based elastic registration of multimodal medical images. The approach uses point landmarks as well as intensity information based on local analytic measures for mutual information. The intensity similarity metrics are computationally efficient and can be optimized independently for each voxel. We have successfully applied our approach to synthetic images, brain phantom images, as well as real multimodal medical images.

ROI-Atlas des menschlichen Gehirns durch neuronale Klassifikation und Konturverfolgung

Zur quantitativen Analyse funktioneller Bilddaten des Gehirns (PET, SPECT) soll die morphologische Modalitat (MRT) der genauen anatomischen Zuordnung funktioneller Parameter dienen. Die kernspintomographischen Schnittbilder werden hierzu durch einen neuronalen Klassifikator in funf Klassen segmentiert. Zur regionenorientierten Auswertung funktioneller Parameter werden die Regionengrenzen anschliesend als geschlossene Polygonzuge aus den Klassenbildern extrahiert. Diese Polygonzuge werden dann als klassifizierte Regionengrenzkonturen in Form eines ROI-Atlantenl der funktionellen Modalitat uberlagert.