Proceedings of the meeting - Department of Physics - University of ...

Improved study of myocardial infarction using contrast enhanced MRIGang Gao 1, 2 , Paul Cockshott 1 , Bjoern Groenning 1 , Annette Sterr 21. University of Glasgow, UK 2. University of surrey, UKP36IntroductionAt present myocardial viability is assessed by visualevaluation of wall motion abnormalities fromcinematographic (CINE) magnetic resonance (MR)images in combination with presence or absence of latehyper enhancement (LE) on contrast enhanced MR(ceMR) images. Currently, ceMRI and cine MRI dataare collected separately, and subsequently comparedeach other to derive a viability score 1 . This approachmay face co-registration problem due to image misalignbetween the two sets of breath-hold images. We set outto develop and validate image processing techniquescapable of reducing the observer dependence andimproving accuracy in the diagnosis of viablemyocardium.MethodsData acquisition20 patients with chest pain who were both troponin Iand LE positive were recruited. MR was performed at amedian (range) of 69 (16-120) hrs on a Siemens Sonata1.5T system using a phased array chest coil. LVdimensions were evaluated by CINE trueFISP breathholdsequence. ceMR was performed 10 minutes afterinjection of 0.2 mmol/kg gadolinium-DTPA using abreath hold segmented turboFLASH inversion-recoverysequence. For both cine MRI and ceMRI, images wereacquired from 9 cross-sectional slices (slice thickness =8mm) to cover the entire heart.CINE-LE MR imagesReference images were selected manually at a timepoint t during a cardiac cycle from all 9 slices. Firstly, amutual information based 3D affine image registrationalgorithm 2 was used to correct the motion between thereference images and the ceMR images. Secondly, thecorrected reference images were registered with theother CINE images by a 3D non-rigid image registrationalgorithm 2,3,4 , producing a set of 3D array, whichspecify for each pixel in the reference images, thelocation of its corresponding point in the other CINEimages. Using the arrays, it is possible to animate theLE images in a process known as "warping" creatingwarped CINE-LE images.ResultsFrom the 20 patients, data were manually extractedfrom both original and warped images using in-houseoff line software. Mean (SD) LV end diastolic volume(EDV) was measured by planimetry (original/ warped)= (original / warped) = 206 / 215 ml. The t-test showsthere is no significant difference between the LV EDVof the original image and the warped image (p = 0.35 >0.05). Left ventricle end systolic volume (ESV) = 129 /123 ml, p = 0.33. Examples are presented in figure 1and 2.Figure 1. The end diastolic and the end systolic frames of a cinecontrast enhanced sequence. The arrows suggested the potentialhibernating myocardium.Figure 2. An other example of CINE-LE MR images.ConclusionA novel method for cardiac viability assessment usingcombined CINE and ceMR images has been developed.We have shown that there are no significant differencesin left ventricle end diastole volume and end systolevolume between the original CINE and ceMR images.The method therefore appears to be promising as animproved viability assessment tool.References1. Kim RJ, et al, “Relationship of MRI delayed contrastenhancement to irreversible injury, infarct age, andcontractile function”, Circulation, 1999;100:1992-20022. LG Brow, “A Survey of Image RegistrationTechniques”, ACM Computing Surveys, pp.325-376,January, 19923. Thevenaz, U.E., et al., “A pyramid approach tosubpixel registration based on intensity,” IEEE Trans.Image Processing, vol.7, pp. 27-41, 1998.4. H. Mahrholdt, et al., “Relationship of contractilefunction to transmural extent of infarction in patientswith chronic coronary artery disease”, J Am CollCardiol. 2003 Aug 6;42(3):505-12.