Voxel Isotropic

Fig. 5.2.3 Identification of rivulets and surface wetting in a packing of 5-mm diameter glass spheres contained within a column of inner diameter 40 mm. The data were acquired in a 3D array with an isotropic voxel resolution of 328 xm x 328 pm x 328 [im. (a) The original image of trickle flow is first binary gated, so that only the liquid distribution within the image is seen (white) gas-filled pixels and pixels containing glass spheres show up as zero intensity (black), (b) The liquid distribu-...

Obtaining isotropic voxels by combination of fast SI techniques with concepts of parallel data acquisition. 

Use of the thinnest slice thickness justifiable (isotropic voxels where needed). 

Optimal abdominal MDCT data acquisition for 3D evaluation is determined by the scanner available, clinical indication, choice of oral and IV contrast material, and knowledge of the risks of radiation. A list of the current NYU MDCT protocols for specific indications are listed at the end of this chapter. These protocols were developed to allow optimal CT data acquisition for both 2D and 3D data interpretation while trying to limit radiation dose to the patient. By obtaining thin section MDCT data, 3D data interpretation is facilitated by the use of isotropic voxels which enable both MPR and volume rendering to be performed. 

The ideal volumetric dataset, which respect precisely the imaged structures, is obtained when all voxels are isotropic, and therefore their shape is cubic. Unfortunately conventional CT and spiral CT did not fulfill completely these acquisition requirements. Dedicated MR sequences and multi-row detector CT (over 16 slices) overcome this limitation generating isotropic voxels and reducing motion artifacts thanks to faster acquisition protocols. 

Multi-row technology allows sub-millimetric spatial resolution, which is extremely important in the z-axis, thus providing additional information when compared with single-slice CT. The visualization of thin structures such as the stapedial crura and the ossicular ligaments results in being improved by means of multi-row CT also the ability to obtain volumetric data with isotropic voxels permits reliable image reformations in any plane of a section. 

In these last few years, even if ERCP and MRCP still represent an important diagnostic step in diagnosis and characterisation of cystic neoplasm, MDCT has strongly contributed to the depiction and the evaluation of these tumours. Particularly, the introduction and the use of very small detector size and the possibility of acquiring data from quite isotropic voxels have permitted the improvement of the reformatted imaging quality. 

In principle, using similar parameters on both SSCT and MDCT results in wider anatomic coverage and faster scanning time with MDCT. On the other hand, MDCT provides sub-millimeter collimation, improves z-axis resolution and generates isotropic voxels, thus resulting in better image quality of reformatted planes as well as three-dimensional reconstructions. The drawback is represented by data... 

Subsequently, the same authors took advantage of the faster data acquisition provided by MDCT and demonstrated better bowel distension and fewer respiratory artefacts with a beam collimation (5.0 mm) and an effective radiation dose (4.7 mSv for men 6.7 mSv for women) comparable to those of SSCT (Kara et al. 2001). A different proposed approach was to use a thin (i.e., 1.0 mm) beam collimation protocol to obtain images with near isotropic voxels, but simultaneously decrease the effective mAs to 50 in order to keep the effective radiation dose to a level comparable to that of SSCT (5.0 mSv for men and 7.8 mSv for women) (Macari et al. 2002). Such a protocol provided excellent sensitivity for detection... 

Note all values above represent isotropic voxel dimensions. 

STRAFI methods rely on sample translation and so the precision and reproducibility of the mechanical arrangement also limits the resolution, here to approximately 10 m. STRAFI methods are also set up to provide isotropic voxels in 3D-imaging, although much work has been done with ID-STRAFI measurements where the question has been carefully tailored so they can be answered by studying profiles of the sample. 

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