Figure 1. Example block detector ring and system: at left a single ring composed of 16 blocks of two different types; at right a tomograph composed of three copies of the ring, with the middle ring rotated by 45 degrees.  (Figure taken from the main Detector Module page in the Users' Guide.)

The rings in the tomograph consist of two different sorts of blocks, shown in the following figure:

(These figures don't show the size of the block and rings, but we will give them plausible dimensions as we build them below - not to say the resulting tomograph is realistic!)

Using define_regular_block.m to create a block

The following cut and paste from a MATLAB session shows how we used the MATLAB function define_regular_block.m to define a block like Block B shown above in Figure 2 (blue, boldface type indicates user response; when the only response is a carriage return we show a '↵'; red type preceded by a % indicates comments):

>> define_regular_block();


Creating a detector block parameter file for SimSET.

This program creates regular scintillator arrays with
block housing and crystal wrapping as the only additional
options.  Another program, define_block.m, allows for more
general arrays.  See the website for more info.

Please enter the file name for the block parameters: example_block_b.blocparms
Please enter the following information for the header.
Author name: Robert
Enter comment -
terminate with 2 consecutive carriage returns:
A four-by-four array of scintillator crystals with aluminum/tungsten
housing and tungsten inter-block housing.
↵

Now define the block geometry and materials.

How many scintillator elements (e.g. crystals) are there
        in the transaxial (y) direction: 4
        in the axial (z) direction: 4

What are the dimensions of these elements in the
        in the radial (x) direction (cm): 2.5  % this is the crystal depth
        in the transaxial (y) direction (cm): 1
        in the axial (z) direction (cm): 1

The transaxial and axial sides of the scintillator elements
can have a layer of wrapping.(e.g., paint or tape).
    Are these elements wrapped? (y/n) [y]: ↵ % values in brackets like this [y]
                                              % are default responses and can be
                                              % accepted by hitting return.
    How thick is the wrap (note this will be doubled between crystals) (cm)? 0.1

There can be housing material on the transaxial and axial
sides of the scintillator block.
    Is there housing material on these sides? (y/n) [y]: ↵
    How thick is the housing on the axial and transaxial sides (cm)? 0.1

Radially there can be up to two layers of uniform material in front of
and behind the scintillator array (e.g. module housing).
    How many layers of material are there before the scintillator (0, 1, or 2)? 1
        How thick is radial layer 1 (cm)? 0.2
    How many layers of material are there after the scintillator (0, 1, or 2)? 1
        How thick is radial layer 1 (cm)? 0.2

Now define the materials used.

Default material indices from phg.data/phg_att_table:
air                    0      con_tissue               15
water                  1      copper                   16
blood                  2      perfect_absorber         17
bone                   3      LSO                      18
brain                  4      GSO                      19
heart                  5      aluminum                 20
lung                   6      tungsten                 21
muscle                 7      liver                    22
lead                   8      fat                      23
NaI                    9      LaBr3                    24
BGO                    10     polycarbonateLowVisc     25
iron                   11     polyethyleneNEMA         26
graphite               12     polymethylMethacryl      27
tin                    13     polystyreneFibers        28
GI_tract               14

When using the default phg_att_table, you can use these material
indices to answer the following.  If, however, you are using a
custom table you should use the indices appropriate to that table.
What is the scintillator material: 10  % BGO
What is the wrap material: 21   % tungsten
What is the housing material on the axial and transaxial sides: 21
What is the material for the first radial layer in front of the scintillator: 20   % aluminum
What is the material for the first radial layer behind the scintillator: 20
>>

A file defining Block A from figure 2 can be found below.  Note that the block definition scripts cannot currently create this block - the scripts require that the blocks include at least one active (e.g. scintillating) element.  (This is a bug that will be fixed in future versions.)

Using define_ring.m to create a ring

The following cut and paste from a MATLAB session shows how we used the MATLAB function define_ring.m to define a ring like those used to build the tomograph in figure 1 (blue, boldface type indicates user response; red type preceded by a % indicates comments):

>> define_ring


Creating a detector ring parameter file for SimSET.

This program fills one ring with block detectors,
prompting the user for the block filenames and positioning
information for each series of blocks.
See the website for more info.

Please enter the file name for the ring parameters: example.ringparms
Please enter the following information for the header.
Author name: Robert
Enter comment -
terminate with 2 consecutive carriage returns:
A ring with 12 detector blocks arranged in a square with three
blocks to a side.  A blade of tungsten bisects each of the empty
corners.  See the web pages for an illustration.
↵

Define the outer bounds of the ring:  the minimum and maximum
axial values in the ring; the radius of a cylinder separating
the detectors from the collimator or object (the inner radius of the the
detector system); and the radius of cylinder that lies entirely
outside the detector system (the outer radius, separating the
tomograph from the rest of the universe).


Radial extent of ring.
Radius of a cylinder separating the detectors from the collimator (cm): 15
Radius of a cylinder separating the detectors from the universe (cm): 25

Axial extent of ring: this is not the final axial position of the ring.
Multiple copies of the ring can be given different axial shifts in
the detector parameter file.
Minimum axial extent of the ring (cm): -2.5   % in general it is easiest to make these
Maximum axial extent of the ring (cm): 2.5    % values +/-0.5 * the block axial extent.



Now specify the blocks in the ring.  The program will prompt
you for a block parameter file, then ask you how many of
this block type are in the ring and how to place them.  This
will be repeated until you have no more blocks you wish to
include in the ring.


Enter the data for block type 1
    Enter file name the block parameters: example_block_b.blocparms
    Radius at which to place the blocks (cm): 15
    Axial position of blocks relative to the ring (cm): 0   % this is usually what you'll want
    How many of this block type? 4   % we are going to start with just the 4 center blocks

    Angular position (azimuth) for first block (degrees): 0
    Are the rest of this block type evenly distributed around the ring? (y/n) [y]: ↵
            % by accepting [y] the other 3 detectors will be placed at 90, 180 and 270 degrees
    The blocks can be rotated in the transaxial plane. A rotation
    of 0 degrees will position the block with its front face tangent
    to the cylinder at the radius given above.  A poistive value
    will rotate the block counterclockwise, a negative value clockwise.

    Angular tilt for first block (degrees): 0
    Do the rest of this block type have this same tilt? (y/n) [y]: ↵


    Add more blocks to the ring? (y/n) [y]: ↵ % we accept the [y] until we have input all the blocks

% now we place four blocks to the clockwise side of the first four
Enter the data for block type 2
    Enter file name the block parameters: example_block_b.blocparms   % we're using the same block type
    Radius at which to place the blocks (cm): 15.8114   % select radius, angular position and tilt to
                                                        % place these blocks next to the first four.
    Axial position of blocks relative to the ring (cm): 0
    How many of this block type? 4

    Angular position (azimuth) for first block (degrees): 18.435
    Are the rest of this block type evenly distributed around the ring? (y/n) [y]: ↵

    The blocks can be rotated in the transaxial plane. A rotation
    of 0 degrees will position the block with its front face tangent
    to the cylinder at the radius given above.  A poistive value
    will rotate the block counterclockwise, a negative value clockwise.

    Angular tilt for first block (degrees): -18.435
    Do the rest of this block type have this same tilt? (y/n) [y]: ↵


    Add more blocks to the ring? (y/n) [y]: ↵

% now we place four blocks to the other side of the first four
Enter the data for block type 3
    Enter file name the block parameters: example_block_b.blocparms
    Radius at which to place the blocks (cm): 15.8114
    Axial position of blocks relative to the ring (cm): 0
    How many of this block type? 4

    Angular position (azimuth) for first block (degrees): 71.565
    Are the rest of this block type evenly distributed around the ring? (y/n) [y]: ↵

    The blocks can be rotated in the transaxial plane. A rotation
    of 0 degrees will position the block with its front face tangent
    to the cylinder at the radius given above.  A poistive value
    will rotate the block counterclockwise, a negative value clockwise.

    Angular tilt for first block (degrees): 18.435
    Do the rest of this block type have this same tilt? (y/n) [y]: ↵


    Add more blocks to the ring? (y/n) [y]: ↵

% now we place four tungsten blades between the rows of blocks
Enter the data for block type 4
    Enter file name the block parameters: example_block_a.blocparms
    Radius at which to place the blocks (cm): 21.3
    Axial position of blocks relative to the ring (cm): 0
    How many of this block type? 4

    Angular position (azimuth) for first block (degrees): 45
    Are the rest of this block type evenly distributed around the ring? (y/n) [y]: ↵

    The blocks can be rotated in the transaxial plane. A rotation
    of 0 degrees will position the block with its front face tangent
    to the cylinder at the radius given above.  A poistive value
    will rotate the block counterclockwise, a negative value clockwise.

    Angular tilt for first block (degrees): 0
    Do the rest of this block type have this same tilt? (y/n) [y]: ↵


    Add more blocks to the ring? (y/n) [y]: n


Ring parameter file generation complete.

ans =

    [1x1 struct]    [1x1 struct]    [1x4 struct]

>>

Creating a tomograph file to use the ring and blocks we created

The final step in creating the block detector parameters is to create the main detector parameter file:  for block detector systems we define the detector system as a stack of rings, plus some general parameters (like energy resolution) which are given for all detector systems.  For our system we stack three copies of the example ring, as defined above, arranged as shown in  figure 1 above.  There is not yet a MatLab script to do this, but the parameter file is quite short and simple compared to the block and ring parameter files.  We give an example block detector parameter file, example.detparms, using the above ring and blocks. 

Together with the block and ring parameter files given below, these files can be placed in a copy of SimSET's samples/fastTest/PETblock directory (you may want to work in a copy of the directory so as not to change the fastTest simulation).  By changing the line in PETblock.phgin that gives the detector parameters file

# DETECTOR PARAMETER FILE
STR     detector_params_file = "PETblock.detparms"

to point to this example's detector parameters file

# DETECTOR PARAMETER FILE
STR     detector_params_file = "example.detparms"

we can run the PETblock simulation using the detector system defined above (you may need to adjust the directory path to the phg executable, depending where you have placed your directory)

% nice ../../../bin/phg PETblock.phgin