High Resolution Detector Modules Based on NaI(T1) Arrays for Small Animal Imaging Page: 3 of 5
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Fig. 2 Top: Raw image obtained with a Na' source. All 34x34 scintillator
pixels are well separated. Bottom: Y-projection of the marked vertical
The best performance with the H8500 was obtained by
directly coupling the array to the PSPMT window. This
coupling includes the 2 mm thick window of the array, in
addition to the 2.8 mm PSPMT window. Since the active
area of the PSPMT is 45mm x 45mm only the center 34 x
34 scintillator elements are in the field of view. In Fig. 2 is
shown a raw image obtained with a Na2 source that flooded
the entire array. All 34 x 34 scintillator pixels are well
separated. Also in Fig. 2 is a Y-projection of the marked
vertical pixel column. Each individual scintillator pixel
element is easily resolved.
B. Imaging oflodine-125
Because the radioisotope I-125 is commonly used for
molecular biology research and is commercially available
linked to nucleic acids, antibodies, and other ligands we were
particularly interested in the performance of the Na(TI) aray
with the detection and imaging of 1-125.
To arrive at a final processed image that would be used in
a small animal imaging system the results of the X and Y
COG calculations to arrive at a raw image are used to identify
which crystal of the array detected an event via a crystal map
look-up table. The sum of all X and Y anode signals is used
to determine if the scintillation event was in the chosen
energy window. Each crystal of the array has a defined
separate energy acceptance window which is stored in an
additional look-up table. The final processed image is formed
by incrementing each pixel corresponding to the crystal
As can be seen in Figs. 1 and 2, images obtained with
PSPMTs exhibit distorted crystal positions because of the
spatially non-uniform response of the PSPMT. Since the
relative position of each crystal is known and the crystal
locations can be defined in the raw image, a distortion
correction is achieved by mapping the data identified to
belong to a particular crystal into that crystal's appropriate
pixel in a corrected image. Fr
table was constructed such
identified by mapping their lo
The data acquisition syst
crystal region individually t
scintillation output variations
variations. For each event th
used to generate a pulse height
125 source an energy calibr
element, Others and oursel,
method with arrays of scintill
a flood image is obtained to pe
the mapped image by using an
We tested the array coupled
with a 0.5mm pinhole tungst
hole collimators constructed
energy radiation of I-125 alloy
lead to construct collimator
resolution and a medium re
beryllium collimator. The co
stacks of layers of copper-be
glued together for a total th
resolution copper collimator i
openings 0.2 x 0.2 mm2 in ar
septa. The medium resolution
0.75 x 0.75 mm2 in area sep
with a total thickness of 0.5
Electron (Tecomet), construct
A simple test phantom was
glass capillary tubes (see Fig.:
-o the flood image a look-up
at individual crystals are
cati n from the flood image.
em treats the output of each
o orrect for crystal-to-crystal
as well as local PSPMT gain
e s m of the anode signals is
it ergy spectrum. Using an I-
ati n is done for each crystal
ves have reported using this
ati g crystals [10, 11]. Finally
rfo a final flood correction cf
I- 25 flood source.
Ito the R2487 PSPMT system
en collimator and two parallel
o t of copper and. The low
vs to use materials other than
s. e have designed a high
;sol tion parallel hole copper-
IF- ators are constructed out cf
rylium (-1.9% Be) laminates
ick ess of 0.5 cm. The high
s 5 cm thick and has square
ea eparated by 0.05 mm thick
c llimator has square opening
ara d by 0.16mm thick septa
c . The company, Thermo
ed a collimator .
co structed with a total of four
Fig: 3: The simple test phantom (top-left) made with three capillaries filled
with 1-125 and one empty capillary as a spacer; center-to-center
spacing 1.473mm, i.d.-0.840mm (the dea glass wall separating the two left
capillaries was therefore 4.63mm th ek). The high resolution etched
copper collimator produced the top-ri t image. The histogram at the
bottom shows a projection along the x-ax s of the capillary phantom image.
Three capillaries were filled
capillary was used as a spacer.
was 1.473 mm, the inner diame
glass wall separating the two left
vith 1-125 and one empty
lhe center-to-center spacing
er is 0.840 mm. The dead
apillaries is therefore -0.63
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Weisenberger, A.G.; Wojcik, R.; Majewski, S. & Popov, V. High Resolution Detector Modules Based on NaI(T1) Arrays for Small Animal Imaging, article, November 1, 2001; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc717797/m1/3/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.