Exxim Computing Corporation. Stacked Volumes


	Scanning and reconstructing large z-size field of view with small detector. Stacked volume mode allows stacking (combining) several (from 2 to 12) cylindrical sub-volumes one on top of the other, thus increasing the effective detector size in V. Several scans (gantry revolutions) must be performed and the gantry (or object) should be moved in z-direction in between the gantry revolution phases. Stacked volumes can be used together with half-beam or 3x view. FIDEX scanner Gantry motion when stacked volume mode is active FIDEX CT scanner manufactured by Animage LLC (subsidiary of Exxim Computing) incorporates all modes providing maximum available field of view. With Varian 13x13 cm flat panel detector FIDEX provides a capability to scan objects up to 24 cm in diameter by 50 cm in length.

Describing a reconstruction task

Within the COBRA reconstruction package, all input, output and intermediate data are kept on the hard disk. The user defines and controls the reconstruction task through a parameter file, a text file with extension .xxm. This file contains tags and assigned values, and describes the scanner hardware setup, input and output data characteristics and representation, and the chosen reconstruction method. Some of the reconstruction options are only accessible through SDK API’s. These are related to synchronization and control of in-line reconstruction (recon concurrent with acquisition), and the setup of COBRA’s working folders.

Tags controlling extended FOV options

PARTAG_SHOWEXTRA

Defines: the fraction of partially illuminated areas on the top and bottom of the field of view that will be shown in the reconstructed slices.
Value type: integer (0-2)
Default value: 1

PARTAG_EXTRAFOVSLICE

Defines: if set to 1 then all voxels in the slice periphery beyond FOV will be shown (not set to zero) in the reconstructed slices.
Value type: integer (0 or 1)
Default value: 0

PARTAG_HBTC

Defines: if set to 1 then half-beam geometry and reconstruction algorithm are effective.
Value type: integer (0 or 1)
Default value: 0

PARTAG_3XVIEW

Defines: if set to 1 then 3x view geometry and reconstruction algorithm are effective.
Value type: integer (0 or 1)
Default value: 0

PARTAG_FASTEXTVIEW

Defines: if set to 1 then half-beam reconstruction algorithm is being performed in draft mode (faster but density values are less accurate).
Value type: integer (0 or 1)
Default value: 0

PARTAG_STACKEDVOLQTY

Defines: If set to value 2 or bigger then stack-volume hardware setup and reconstruction algorithm are effective. It allows combining (stacking) several (from 2 to 12) cylindrical sub-volumes one on top of the other, thus increasing the effective detector size in V. Several scans must be performed and the object should be moved in vertical z-direction in between the scans.
Value type: integer (1-12)
Default value: 1

PARTAG_STACKEDVOLMODE

If PARTAG_STACKEDVOLQTY is set to value 2 or bigger then stack-volume hardware setup and reconstruction algorithm are effective. It allows combining (stacking) several (from 2 to 12) cylindrical sub-volumes one on top of the other, thus increasing the effective detector size in V. Several scans must be performed and the object should be moved in vertical z-direction in between the scans.
If PARTAG_STACKEDVOLMODE =0 then no angular alignment = 0, adjusting volumes only in x,y,z translation;
If PARTAG_STACKEDVOLMODE =1 then adjusting volumes in all 6 degrees of freedom.
Value type: integer (0-1)
Default value: 0

PARTAG_STACKEDVOLOVERLAP

PARTAG_STACKEDVOLOVERLAP defines an upper limit of overlap of stacked subvolumes (%). COBRA will look for 2 slices with maximum similarity and will stitch sub-volumes there.
Value type: integer (1-100)
Default value: 40

PARTAG_STACKEDVOLDIRECTION

If PARTAG_STACKEDVOLQTY is set to value 2 or bigger then stack-volume hardware setup and reconstruction algorithm is effective. It allows combining (stacking) several (from 2 to 12) cylindrical sub-volumes one on top of the other, thus increasing the effective detector size in V. Several scans must be performed and the object should be moved in vertical z-direction in between the scans.
PARTAG_STACKEDVOLDIRECTION defines a direction of object/gantry motion during making sub-volumes. Setting PARTAG_STACKEDVOLDIRECTION to 1 means sub-volume #0 will get highest slice numbers in a combined volume
Value type: integer (0-1)
Default value: 0

PARTAG_STACKEDVOLADJUSTFACTOR

PARTAG_STACKEDVOLADJUSTFACTOR defines a direction of object/gantry motion during making of sub-volumes. Setting PARTAG_STACKEDVOLDIRECTION to 1 means sub-volume #0 will get the highest slice numbers in a combined volume
Value type: integer (0-1)
Default value: 0

PARTAG_STACKEDVOLSEAMLOCATION

PARTAG_ STACKEDVOLSEAMLOCATION defines a slice number where sub-volumes have approximately same slice content. If set, it makes the sub-volume adjustment procedure more reliable and fast.
Value type: integer (0-number of slices in sub-volume)
Default value: 0

PARTAG_PROJ_RECON<NN>

PARTAG_PROJ_RECON defines number of projections to reconstruct, corresponds sub-volume ( #0, #1,…#11)
Value type: integer (0-11)
Default value: 512

PARTAG_PRJ_STARTFROM_3X

When PARTAG_3XVIEW is set to 1 then 3x view hardware setup and reconstruction algorithm are effective. It means that there is a second gantry (object) revolution with a different detector position. PARTAG_PRJ_STARTFROM_3X defines a first projection number belonging to the second gantry revolution.
Value type: integer
Default value: 512

PARTAG_PRJ_RECON_FORWARD_3X

When PARTAG_PRJ_RECON_FORWARD_3X is set to 1 then it is assumed that revolution with the outer detector position has been made first.
Value type: integer (0-1)
Default value: 0

PARTAG_DET_OFFSET_U_3XEXT

PARTAG_DET_OFFSET_U_3XEXT defines the detector position in the direction perpendicular to the axis of rotation.
Value type: float
Default value: 0

PARTAG_DET_OFFSET_V_3XEXT

PARTAG_DET_OFFSET_V_3XEXT defines the detector position in the direction parallel to the axis of rotation.
Value type: float
Default value: 0

Scanning and reconstructing large z-size field of view with small detector.

FIDEX scanner

Gantry motion when stacked volume mode is active