1、會計學1能譜能譜CT圖像質量圖像質量SpatialResolutionImageNoiseContrastResolutionArtifactsPrincipal components of image quality are contrast, spatial resolution, and noise.空間分辨率噪聲密度分辨率偽影Quantifies image blurringOnePairPhantoms Spatial Resolution空間分辨率Display matrix重建算法 焦點尺寸 探測器孔徑 層厚采樣頻率 高清模式空間分辨率Hi Res2496 ViewsImprov

2、e IQLike VCT984 Views Standard Algorithm “Lung” Algorithm濾波算法影響空間分辨率lZ軸分辨率是指設備在Z方向上分辨細節(jié)的能力。l它主要是影響3D圖像的分辨率。如冠狀面或矢狀面的重建l用Z軸方向的投影曲線的半高寬度（FWHM）來表示。通常情況下，Z軸分辨率層厚l目前的高檔的多層螺旋CT的Z軸方向的空間分辨率已經(jīng)接近橫軸面的空間分辨率，就是說基本上達到了所謂“各向同性”Arbitrarily selected planar section at position zzz1z1 + dPlanar data for arbitrary posi

3、tions are calculated from spiral data by interpolationd360 degree algorithm360內插算法的Z軸分辨率會下降30CT 對比度Elemental Composition ofsubjectSubject mass attenuationcoefficientElectron densityPhysical densitythicknessIncident X spectrumWindow and level Viewing factorsViewing human factorssurrounding factors431

4、mcZAS(xi - xmean)2Noise (s) = -(n-1) Xi = individual pixel valueXmean = average of all pixel values in ROIn =total # pixels in ROIUnits(HUs)or% contrastALARA原則As low as reasonable achievables2(m) = kT/(td3R)uIf slice thickness goes down by 2uDose must go up by 2uTo hold noise constant3 mm Slice10 mm

5、 Slice層厚.對于軟組織來講厚的層厚能提供低噪聲、高密度分辨率的圖像。在軟組織研究病例中, 用高mAs來保持低噪聲是非常重要的。因為軟組織比如肝臟上要觀察的細節(jié)與周圍組織往往具有較小的對比度。噪聲的存在會掩蓋這些對比度。因此在軟組織為主的肝臟等部位，需要提高劑量，以降低噪聲提高密度分辨率，以能分辨微小的病變；而在肺或內耳的檢查中，可適當降低掃描條件，因為這些部位本身具有較高的對比度，少量的噪聲不會影響診斷。 mAs(劑量)優(yōu)化門脈期圖像的觀察能量閾值，最佳顯示為52KeVMARS：減除金屬和硬化偽影：減除金屬和硬化偽影s2(m) = kT/(td3R)Wheres is variance resulting from noisek is a conversion factor (constant)T is transmissivity (inverse of attenuation)t is slice thicknessd is pixel sizeR is doseArbitrarily selected planar section at position zzz1z1 + dPlanar data for arbitrary positions are calculated from