Comparison Study Of Coronary Atherosclerotic Plaque With Multiple Imaging Modalities

Part oneHigh Resolution MR Imaging of Coronary Arterial Wall in Vitro:an Experimental Study on PorcineObjective:To get a MR imaging protocol for coronary arterial wall in vitro and assessment of atherosclerotic plaque composition.Materials and methods:MRI examinations were performed in ten fresh porcine hearts.Fast imaging employing steady state acquisition(FIESTA)were used to delineate anterior descending artery(LAD).2D spin-echo T1WI imaging was performed using temporomandibular surface coil,eight-channel head surface coil and knee coil with the same parameters.Then,T1WI was performed with 384x256 or 512x512 in matrix using temporomandibular surface coil.And then 2D T1WI,PDW and T2WI with fat saturation were performed with different NEX using temporomandibular surface coil after injecting Resovist in LAD.Signal of the LAD wall,lumen,fat tissue adjacent to LAD,myocardium of anterior part of interventricular septum and noise were respectively measured.SNR of image, CNR1 between the wall and lumen,CNR2 between the wall and surrounding fatty tissue were calculated.Results:The SNR(72.89)and CNR1(18.18),CNR2(53.32)of SE T1WI with temporomandibular coil were higher than that with eight-channel head surface coil(SNR:12.06;CNR1:4.70;CNR2:6.49)and knee coil(SNR:14.42; CNR1:5.30;CNR2.9.06).The SNR(72.89)and CNR1(18.18),CNR2 (53.32)of SE T1WI with 384X256 matrix were higher than that(SNR:34.18; CNR1:11.72;CNR2:24.85)with 512X512.The SNR(SE T1WI:39.57;frFSE T2WI.27)and CNR1(SE T1WI:34.38;frFSE T2WI:27.60),CNR2(SE T1WI:33.63;frFSE T2WI:22.08)using 3 NEX were highest.Conclusion:The good SNR and CNR of coronary wall can be achieved using temporomandibular surface coil,384X256 in matrix and 3 NEX.Part Two64-slice Spiral CT and MRI Study of Coronary Atherosclerotic Plaques in Vitro:Comparison with PathologyObjective:To assess the values of 64-slice CT and MRI in demonstrating the component of coronary atherosclerotic plaques in vitro.Materials and Methods:Thirteen consecutive autopsy hearts(12 males,mean age 86 years old)were examined after intubating into left main trunk successfully. CT was performed on Siemens sensation cardiac 64 spiral CT scanner with 120 kV,200 eff.mAs,pitch 1.0,slice collimation 64x0.6mm,0.5s/r,scan time 3s, thickness 0.6mm,increment 0.4mm.4 ml contrast agent(omnipaque 350mgI/ml)was infused into 100ml saline and then was injected into LAD.MRI was performed on GE SIGNA 1.5T HD with 3D FIESTA sequence which was used to locate left anterior descending artery(LAD)and the cross-sectional images of 2D T1WI,PDW,frFSE T2WI perpendicular to long axis of LAD were obtained.Scan parameters included:SE T1WI:TR 440ms,TE 21ms,FOV 12cmx9cm,thickness 2mm,slice space 0.2mm,matrix 512x512,NEX 2;SE PDW:TR 2000ms,TE 21ms,FOV 12cmx9cm,thickness 2mm,slice space 0.2mm,matrix 512x512,NEX 2;frFSE:TR 4500ms,TE 105ms,FOV 12cmx9cm, thickness 2mm,slice space 0.2mm,matrix 512x512,NEX 2.0.2ml Resovist (0.5mmol Fe/ml)was infused into 100ml saline and then injected into LAD before PDW and T2WI started.Standard pathologic sections were obtained corresponding to the MRI and CT images perpendicular to LAD.CT,MRI images and pathologic sections were independently reviewed,categorized and compared. The sensitivity,specificity of CT and MRI classification of plaques were analyzed respectively using diagnostic test.Results:Ninty-four histological sections were matched with CT and MRI images. The sensitivity and specificity,respectively,of CT for categorizing each lesion type were as follows:typeⅠ-Ⅱ,0%and 100%;typeⅢ,0%and 100%; typeⅣ-Ⅴ,92.3%and 86.8%;typeⅥ,0%and 100%;typeⅦ,100%and 100%;typeⅧ,100%and 97.8%.The mean CT values for each lesion type were as follows:typeⅣ-Ⅴ,53.7HU;typeⅦ,1065HU;typeⅧ,89.3HU.The sensitivity and specificity of MRI for categorizing each lesion type were as follows:typeⅠ-Ⅱ,60%and 100%;typeⅢ,80%and 100%;typeⅣ-Ⅴ,96.2%and 86.8%;typeⅥ,100%and 98.9%;typeⅦ,93%and 100%; typeⅧ,100%and 98.9%.Slightly high signal on MRI images representing lipid component pathologically could be detected in 48.8%calcified lesions. Neovascularization could be found in 45.7%histological sections.The neovascularization and inflammatory cells on histological sections were found in 50%of typeⅣ-Ⅴlesions,100%of typeⅥlesions,58%of typeⅦlesions and 100%of typeⅧlesions.Conclusions:MRI is superior to CT for demonstrating the characteristics of coronary atherosclerotic plaques and plaque classification.Inflammatory cells and neovascularization in the lesions can promote instability of plaques and be dramatically increased in the advanced lesions. Part ThreeEvaluating the Enhancement of Atherosclerotic Plaque on Contrast-enhanced MRA:Comparison with CTAObjective:To evaluate the enhancement of coronary atherosclerotic plaque revealed by CTA using pre- and post-contrast navigator-gated 3D-SSFP sequence and the relationship between plaque enhancement on contrast-enhanced MRA and CT value of the plaque.Materials and methods:Nineteen patients(mean age 56 years old,15 males) with non-calcified or mixed plaques with main non-calcified component on the proximal or middle segments of coronary artery detected by MDCT were recruited for MRA study with GE 1.5T HD MRI scanner.The coronary MRA was performed using a navigator-gated 3D-SSFP sequence before and after administration of Gd-DTPA.Coronary MRA was acquired 2～3 times after Gd-DTPA administration on the segments with plaques.30ml Gd-DTPA was injected with biphase:10ml at a flow rate of 1.5ml/s and 20ml at 0.05ml/s.The cross-sectional images perpendicular to the long axis of coronary artery were reformatted on MRA.The locations of plaques on MRA were corresponding to sites on CTA,at the same distance to the origin or bifurcation.Plaque enhancement was assessed using CNR(contrast-to-noise ratio:signal of plaque minus signal of adjacent fat tissue divided by noise).An 50%increasing of CNR was defined as enhancement.The relationship between CNR increment and CT value was analyzed.Signal of the aortic root and thoracic muscle were measured and SNR(signal-to-noise:signal of aortic root divided by noise)and CNR(signal of aortic root minus signal of thoracic muscle divided by noise)were calculated pre- and post-contrast MRA.Image quality were compared before and after contrast injection using t-test.Results:Twenty-four plaques of 14 patients were identified on both pre- and post-contrast MRA at the corresponding site of CTA.11 plaques showed enhancement and 13 plaques showed no enhancement.Of 11 enhanced plaques,5 plaques showed enhancement at 5 minutes after contrast injection,others at 10-15 minutes.Of 13 unenhanced plaques,4 plaques showed high signal on pre-contrast scan and others showed low signal.It is helpful to differentiate plaques and lumen after contrast injection.CNR between 24 plaques and surrounding fat tissue were respectively 10.29±4.28 and 14.08±5.8 in pre- and post-contrast MRA and there was a significant difference(P＜0.01).CNR were significantly increased from 8.43±3.59 to 17.55±6.18 after contrast administration in 11 enhanced plaques and no significant change(11.86±4.3 versus 11.15±3.48)in 13 non-enhanced plaques. There was no significant difference of CT value between the enhanced plaques (68.44±24.72)and non-enhanced plaques(57.82±24.13).There was no relationship between CNR increase of coronary atherosclerotic plaque on MRA and CT value.The SNR and CNR at 5 minutes after contrast injection (35.37±6.84 and 21.57±6.08)were significantly higher than that of pre-contrast MRA(27.38±6.24 and 13.19±6.50).The SNR at 15 minutes after contrast injection(33.81±9.43)was higher than that of pre-contrast MRA,but there was no statistically difference.The CNR at 15 minutes after contrast injection(21.20±7.65)was significantly higher than that of pre-contrast MRA.The SNR and CNR at 15 minutes after contrast injection were no significant differences compared with that at 5 minutes after contrast injection.Conclusions:Enhancement of coronary atherosclerotic plaques can be demonstrated on CEMRA.Enhancement of plaques may be associated with inflammation,fibrosis and neovascularization pathologically,predicting the vulnerability of atherosclerotic plaques.The enhancement of plaques on MRA has no relationship with CT value on CTA.T1-shorting effect in the blood can be prolonged by quick injection combining with slow infusion of Gd-DTPA and the SNR and CNR can be improved during multiple scans of coronary MRA compared with pre-contrast MRA. Spiral computed tomography;Contrast mediaPart FourThe Accuracy of Assessing Coronary Atherosclerotic Plaque by 64-Slice Spiral CT:Comparison with IVUSObjective:To assess the value of 64-slice spiral CT in demonstrating coronary atherosclerotic plaque composition and quantification of plaque burden by comparison with intravascular ultrasound(IVUS).Materials and Methods:Fourteen patients(9 males,mean age 58 years)with atherosclerotic plaques on the proximal or middle segments of coronary artery demonstrated by MDCT were included.IVUS was performed after CT examination within a week.The coronary angiography(CTA)was performed using Siemens Sensation Cardiac-64 MDCT.Coronary arteries were reconstructed using MIP and MPR and the cross-sectional images perpendicular to the long axis of coronary artery were obtained.The CT values of the plaques were measured. The plaques were classified as soft,fibrotic and calcified plaques according to CT values.The minimum lumen area(MLA),external elastic membrane cross sectional area(EEM CSA)were measured and plaque area,plaque burden were calculated.The composition of plaques were confirmed by IVUS and the MLA, EEM CSA,plaque area,plaque burden measured or calculated by MDCT were compared with IVUS.The sensitivity and specificity of classifying plaques types by MDCT were assessed and average CT value of every type plaque was acquired.Results:Total 25 plaques were included in this study.The average CT value of 11 soft plaques was 49±32HU,7 fibrotic plaques was 93±23HU,7 calcified plaques was 1138±350HU.The sensitivity and specificity of MDCT for identifying soft plaques were 90.9%and 92.9%,85.7%and 94.4%for fibrotic plaques,100%and 100%for calcified plaques.Vessel area,lumen area,plaque area and plaque burden measured or calculated by MDCT(16.2±5.1mm~2, 6.58±4.1mm~2,9.61±3.8mm~2,60±18%)were higher than those by IVUS (14.5±4.8mm~2,6.28±4.3mm~2,8.22±3.6mm~2,58.5±20.1%),but there was no statistical difference.Conclusion:64-slices MDCT is an accurate and noninvasive tool for assessment of coronary atherosclerotic plaques composition and quantification of plaque burden.