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Characteristics of miniature CsI photodiode detectors for gamma ray and their clinical applications
Nuclear Instruments and Methods in Physics Research A 353 (1994)
453-456
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH Section A
ELSEVIER
Characteristics of miniature Csl photodiode detectors for gamma ray and their clinical applications M.Q. Makino
a, *,
K. Kawakami
a,
K. Kanaya
b,
S. Kanaya
b,
S. Tange
b,
K. Kusakabe
b
a The Jiket University School of Medicine, Minato-ku, Tokyo, Japan b Tokyo Women's Medical College, Shmjuku-ku, Tokyo, Japan
Abstract Miniature Csl photodiode detectors were built. Their physical characteristics were examined . Two probes with the Csl detectors were used for measurements of gamma rays from various nuclides in animals and in humans . The applicability and usefulness of the CsI photodiode detector and its limitations will be described. 1. Introduction Recently probes for gamma ray, replacing PM tubes for photodiodes, were reported in medical applications in Refs . [1,2]. We decided, therefore, to build miniature Csl photodiode detectors and examined the physical characteristics of the detectors and their limitations, and possibilities of applying the miniature detectors to clinical applications .
nite slabs of CsI with different thickness. Fig. 3 shows the results of the calculations for CsI(TI) with 2 mm, 4 mm and 10 mm in thickness, respectively, for gamma ray energies up to 1 MeV. In these calculations the following is considered : the probability of photoelectric absorption per atom is proportional to the nth power of the atomic
20K
2. Method
y C O
The Csl detector consists of a Csl crystal [3] and a photodiode [4]. Two different detector thicknesses are produced. Both have an area of 12 mm X 12 mm and their thicknesses are 10 mm and 2 mm, respectively . The photodiode has an active area of 10 mm X 10 mm . They are optically coupled with epoxy resin. For these detectors we examined both the energy resolution and linearity. The signals from the detector are amplified through a charge sensitive pre-amp, pulse-shaped in the main amplifier, and then fed into a multichannel analyzer . We obtained energy resolutions of 55%, 25%, and 9% for gamma rays of 80 keV, 140 keV, and 662 keV, respectively . Fig. 1 shows these energy spectra. In Fig. 2 the linearity of the detector is shown. These measured points are obtained from various 201 nuclides such as T1, 99-Tc, 133Ba, 22 Na, 137Cs, and 60 Co . Good linearity of the detector for gamma rays is demonstrated from 80 keV to 1 meV within errors . In order to determine the efficiency of CsI(TI) crystal for gamma rays, the calculations were performed for infi-
* Corresponding author . Tel. Fax + 81 3 3435 1922.
+81 3 3433 1111
0168-9002/94/$07 .00 C 1994 Elsevier SSDI0168-9002(94)00796-9
(ext .
3361),
0
100
500
1000
500
1000
500 h
â ô U
J
100
5K
we
0 0
U
0
100
500
Channel
1000
Fig. 1. With the CsI(Tl) detector energy resolutions of 55%, 25% and 9% are obtained for gamma rays of 80 keV, 140 keV and 662 keV, which correspond from the top to the bottom spectra, respectively .
Science B.V . All rights reserved
VIIIa. BIOMEDICAL APPLICATIONS
M.Q. Maktno et al. I Nucl. Instr and Meth . i n Phys . Res. A 353 (1994) 453-456
454 KeV
.y i y u
1500 bA C W
NaI
0 ^Ô
1000
Csl l
500
0
100
50
150
200
Channel Fig . 2. Linearity of the detector is represented by the measured points .
number Z and inversely proportional to the 3.5th power of the incoming energy E [5]. The densities and the effective atomic numbers of Nal(TI) and CsI(TI) are 3.67, 4.51 (g/cm3 ) and 50, 54 respectively [6]. Since the photoelectric absorption coefficient for CsI(TI) is not available it is approximated using the photoelectric absorption coefficient of Nal(TI) with n = 5 [5]. The actual efficiencies for a finite size of the detectors are further reduced to 10-20% from the results given in Fig. 3 . For both clinical and biological applications of these detectors, two kinds of probes are built. One is for general usage, made of an aluminum case . Its dimension is 18 mm X 18 mm X 75 mm and contains a Csl photodiode detector and pre-amp. The other is for measurement of left ventricular ejection fraction (LVEF) . The miniature probe is housed in a cylindrical aluminum case 50 mm in diameter and with a height of 32 mm . It contains a Csl photodiode detector with a single hole lead collimator 10 mm in diameter and 5 mm long; the detector is surrounded by 4
Csl(TI)
100-
10
30
50
100
300 500 1000
Energy (KeV) Fig. 3 . Detector efficiency of Csl(TI) crystal for gamma rays up to 1 MeV . Three curves are shown.
i
I 60
,
I 1 120 (sec)
Fig . 4 . While a normal volunteer was breathing 81 . Kr gas, radioactive wave-like patterns of respiration changes of both CsI(T0 and Nal(tl) PM detectors, placed on his both lungs, were recorded .
mm lead shielding and also a pre-amp is built inside the case . The output signals from the main amplifier are selected by a SCA and selected pulses are interfaced into a personal computer . Within the computer 1 MHz programmable counters are actuated during a temporal interval and counts/ interval are stored in the memory and simultaneously a time activity curve is displayed on the CRT . 3. Applications 3.1 . Pulmonary i)entilation study A normal volunteer was in the sitting position . One Nal PM (5 in . in diameter, 3 in . in thickness) was placed near the left frontal lung, the other CsI detector on the right frontal lung . While he was breathing 370 MBq of s'm Kr gas, radioactive wave-like patterns of respiration changes of both detectors were recorded corresponding to inspiring and expiring deeply . Fig. 4 shows those time active curves obtained from both detectors. In Fig. 5, after a normal volunteer was breathing 370 133 MBq of Xe-133 for 3 min, a wash-out pattern was
0
1
2
3
4 (rain)
133Xe Fig . 5 After a normal volunteer was breathing 370 MBq of for 3 mm a wash-out pattern was recorded with a Csl(TI) detector that was placed on the middle of the lung field.
M. Q. Makino et al. /Nucl. Instr. and Meth. i n Phys . Res. A 353 (1994) 453-456
455
3.3 . Brain study lung
One CsI probe was placed on the lung field, the other CsI probe was placed on the right lateral neck. Then the 123, patient was intravenously injected with 74 MBq of
v
E C 0 0
IMP. In Fig. 6 the upper curve represents the time activity curve of the lung, while the lower curve represents that of
the neck for 60 s. The time necessary for the radioactivity
1200
to reach saturation is used for the calculation of a regional
U
brain blood volume .
3.4. First pass of LVEF 0
In Fig. 7 the upper curve shows the first pass radiocar-
Fig. 6. The upper curve represents the time activity curve of the lung, while the lower that of the neck for 120 s, after injection of 123, 74 MBq of IMP.
diogram of left ventricle (LV) after injection of 555 MBq of
99mTc
HSAD . The lower curve shows a similar time
activity curve to that of the first pass in the upper, after
recorded with a CsI detector that was placed on the middle of the lung field. The half-life resulting from the wash-out curve was 40 s, while the half-life obtained from the scintillation camera that was taking data simultaneously, turned out to be the equivalent value of 38 s.
3.2 . Animal test A probe with a single hole collimator (8 mm in diame-
ter) was used for testing a rat. 15 Mbq of
99mTc
MIBI
(which is equivalent dose to human) was injected intra-
venously into a rat after it being anesthetized with pentbar-
bital sodium . Then the probe was placed near the heart field. The time activity was measured, indicating that the radioactivity rises sharply, then falls quickly, and remains
constant for a long period . For 201 T1 chloride a similar time activity curve was obtained .
1400
v 'v
U
"
0 t~ 0 h
a
1400
U
ii Y
IJ J
0
°"f~nNU"JVf1
30 sec
0 0 u
30
sec Fig. 7. The upper curve shows the first pass radiocardiogram of LV after injection of 555 MBq of 99m Tc HSAD . The lower curve is the time activity curve, after injection of 185 MBq of the rest of 99mTc the HSAD.
Fig. 8. On the image, accumulations of 67 Ga citrate are clearly seen on both primary tumor and its lymphonode metastasis . The lower figure shows the distribution of counting rates (CPS) measured by the probe around region of the neck . VIIIa . BIOMEDICAL APPLICATIONS
456
M.Q. Makino et al. INucl. Instr. and Meth. t o Phys. Res. A 353 (1994) 453-456
injection of 185 MBq of the rest of
99'Tc
HSAD . This is a
typical first pass radiocardiogram of LV we have measured by a small EF probe. These data are obtained from a counting rate with 50 ms intervals, then later processed with a time sequence digital filter . 3.5 . Lymphoma In Fig. 8 the upper picture shows a tumor scintigraphy
of malignant lymphoma, right lingual tonsil of primary origin taken three days after injection of 111 MBq of 67Ga citrate. A swelling of right submandibular lymphonode
was observed . On the scinticamera image, accumulations
of 67Ga citrate are clearly seen on both primary tumor and its lymphonode metastasis . The lower figure shows the distribution of counting rates (CPS) measured by the probe around the region of the neck. Among them two higher
CPSs are observed, which correspond to the dense accu67 mulations of Ga citrate on the image.
4. Discussion For the above applications probes of 10 mm thickness of CsI(TI) crystal were used . The efficiency of the detector is rapidly decreased beyond the 200 keV of the incoming
gamma rays . The radionuclides used in the applications are 201 133 67Ga, and 81 ~Kr. Using the probes, TI, Xe, 99'Tc, emitting gamma rays from those nuclides are measured with sufficient detection efficiency .
The maximum wavelength emitted from CsI(Tl) is 540
nm [6] and the maximum sensitivity of the PIN photodiode used lies at 900 nm and its sensitivity is reduced to almost
one half at a wavelength of 540 nm [8]. The maximum noise level observed is around 30 keV at the room temperature.
5. Conclusion We have examined CsI(Tl) photodiode detectors re-
garding the energy resolution, the linearity of the detector,
and the efficiency for gamma ray, and we have shown
applications of the probes to biology and medicine .
CsI(Tl) miniature probes have characteristics of small
size and light weight with relatively higher efficiency for gamma rays, and yet they require no higher voltage. No housing, therefore, for voltage dividers is needed . Both CsI(TI) and photodiode are not expensive. The probes are rugged .
The CsI(Tl) probe is, however, not applicable for measurements requiring high energy resolution, but for rather biomedical applications, as we have shown, such as biological experiments using animals, radio immuno-guided surgery, localized measurements of time activity curves, and measurements of LVEF. The possible low energy limit for measuring gamma rays, therefore, seems to be around 50 keV.
References [11 D. Hunter, R. Lawrence, C. Morgan and T. Evans, Nucl . Med. Comm 11 (1990) 879. [2] P. Broadhurst, P Cashman, J. Crawley, E. Raftery and A. Lahiri, J. Nucl. Med. 43 (1991) 37 . [3] made by Horiba Ctystal Co ., Tokyo, Japan. [4] Manufactured by Hamamatu Photoelectronics, Hamamatu, Shizuoka, Japan. [5] C.M. Davisson and R.D. Evans, Rev . Mod. Phy. 81 (1951) 404. [6] K. Knoll, Radiation Detection and Measurement, 2nd ed . (Wiley, New York, 1979) p. 231. [7] R.D . Evans, The Atomic Nucleus (McGraw-Hill, New York, 1941) p. 717. [8] Photodiode specification sheets, Hamamatu Photoelectronics, Hamamatu, Shizuoka, Japan.
453-456
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH Section A
ELSEVIER
Characteristics of miniature Csl photodiode detectors for gamma ray and their clinical applications M.Q. Makino
a, *,
K. Kawakami
a,
K. Kanaya
b,
S. Kanaya
b,
S. Tange
b,
K. Kusakabe
b
a The Jiket University School of Medicine, Minato-ku, Tokyo, Japan b Tokyo Women's Medical College, Shmjuku-ku, Tokyo, Japan
Abstract Miniature Csl photodiode detectors were built. Their physical characteristics were examined . Two probes with the Csl detectors were used for measurements of gamma rays from various nuclides in animals and in humans . The applicability and usefulness of the CsI photodiode detector and its limitations will be described. 1. Introduction Recently probes for gamma ray, replacing PM tubes for photodiodes, were reported in medical applications in Refs . [1,2]. We decided, therefore, to build miniature Csl photodiode detectors and examined the physical characteristics of the detectors and their limitations, and possibilities of applying the miniature detectors to clinical applications .
nite slabs of CsI with different thickness. Fig. 3 shows the results of the calculations for CsI(TI) with 2 mm, 4 mm and 10 mm in thickness, respectively, for gamma ray energies up to 1 MeV. In these calculations the following is considered : the probability of photoelectric absorption per atom is proportional to the nth power of the atomic
20K
2. Method
y C O
The Csl detector consists of a Csl crystal [3] and a photodiode [4]. Two different detector thicknesses are produced. Both have an area of 12 mm X 12 mm and their thicknesses are 10 mm and 2 mm, respectively . The photodiode has an active area of 10 mm X 10 mm . They are optically coupled with epoxy resin. For these detectors we examined both the energy resolution and linearity. The signals from the detector are amplified through a charge sensitive pre-amp, pulse-shaped in the main amplifier, and then fed into a multichannel analyzer . We obtained energy resolutions of 55%, 25%, and 9% for gamma rays of 80 keV, 140 keV, and 662 keV, respectively . Fig. 1 shows these energy spectra. In Fig. 2 the linearity of the detector is shown. These measured points are obtained from various 201 nuclides such as T1, 99-Tc, 133Ba, 22 Na, 137Cs, and 60 Co . Good linearity of the detector for gamma rays is demonstrated from 80 keV to 1 meV within errors . In order to determine the efficiency of CsI(TI) crystal for gamma rays, the calculations were performed for infi-
* Corresponding author . Tel. Fax + 81 3 3435 1922.
+81 3 3433 1111
0168-9002/94/$07 .00 C 1994 Elsevier SSDI0168-9002(94)00796-9
(ext .
3361),
0
100
500
1000
500
1000
500 h
â ô U
J
100
5K
we
0 0
U
0
100
500
Channel
1000
Fig. 1. With the CsI(Tl) detector energy resolutions of 55%, 25% and 9% are obtained for gamma rays of 80 keV, 140 keV and 662 keV, which correspond from the top to the bottom spectra, respectively .
Science B.V . All rights reserved
VIIIa. BIOMEDICAL APPLICATIONS
M.Q. Maktno et al. I Nucl. Instr and Meth . i n Phys . Res. A 353 (1994) 453-456
454 KeV
.y i y u
1500 bA C W
NaI
0 ^Ô
1000
Csl l
500
0
100
50
150
200
Channel Fig . 2. Linearity of the detector is represented by the measured points .
number Z and inversely proportional to the 3.5th power of the incoming energy E [5]. The densities and the effective atomic numbers of Nal(TI) and CsI(TI) are 3.67, 4.51 (g/cm3 ) and 50, 54 respectively [6]. Since the photoelectric absorption coefficient for CsI(TI) is not available it is approximated using the photoelectric absorption coefficient of Nal(TI) with n = 5 [5]. The actual efficiencies for a finite size of the detectors are further reduced to 10-20% from the results given in Fig. 3 . For both clinical and biological applications of these detectors, two kinds of probes are built. One is for general usage, made of an aluminum case . Its dimension is 18 mm X 18 mm X 75 mm and contains a Csl photodiode detector and pre-amp. The other is for measurement of left ventricular ejection fraction (LVEF) . The miniature probe is housed in a cylindrical aluminum case 50 mm in diameter and with a height of 32 mm . It contains a Csl photodiode detector with a single hole lead collimator 10 mm in diameter and 5 mm long; the detector is surrounded by 4
Csl(TI)
100-
10
30
50
100
300 500 1000
Energy (KeV) Fig. 3 . Detector efficiency of Csl(TI) crystal for gamma rays up to 1 MeV . Three curves are shown.
i
I 60
,
I 1 120 (sec)
Fig . 4 . While a normal volunteer was breathing 81 . Kr gas, radioactive wave-like patterns of respiration changes of both CsI(T0 and Nal(tl) PM detectors, placed on his both lungs, were recorded .
mm lead shielding and also a pre-amp is built inside the case . The output signals from the main amplifier are selected by a SCA and selected pulses are interfaced into a personal computer . Within the computer 1 MHz programmable counters are actuated during a temporal interval and counts/ interval are stored in the memory and simultaneously a time activity curve is displayed on the CRT . 3. Applications 3.1 . Pulmonary i)entilation study A normal volunteer was in the sitting position . One Nal PM (5 in . in diameter, 3 in . in thickness) was placed near the left frontal lung, the other CsI detector on the right frontal lung . While he was breathing 370 MBq of s'm Kr gas, radioactive wave-like patterns of respiration changes of both detectors were recorded corresponding to inspiring and expiring deeply . Fig. 4 shows those time active curves obtained from both detectors. In Fig. 5, after a normal volunteer was breathing 370 133 MBq of Xe-133 for 3 min, a wash-out pattern was
0
1
2
3
4 (rain)
133Xe Fig . 5 After a normal volunteer was breathing 370 MBq of for 3 mm a wash-out pattern was recorded with a Csl(TI) detector that was placed on the middle of the lung field.
M. Q. Makino et al. /Nucl. Instr. and Meth. i n Phys . Res. A 353 (1994) 453-456
455
3.3 . Brain study lung
One CsI probe was placed on the lung field, the other CsI probe was placed on the right lateral neck. Then the 123, patient was intravenously injected with 74 MBq of
v
E C 0 0
IMP. In Fig. 6 the upper curve represents the time activity curve of the lung, while the lower curve represents that of
the neck for 60 s. The time necessary for the radioactivity
1200
to reach saturation is used for the calculation of a regional
U
brain blood volume .
3.4. First pass of LVEF 0
In Fig. 7 the upper curve shows the first pass radiocar-
Fig. 6. The upper curve represents the time activity curve of the lung, while the lower that of the neck for 120 s, after injection of 123, 74 MBq of IMP.
diogram of left ventricle (LV) after injection of 555 MBq of
99mTc
HSAD . The lower curve shows a similar time
activity curve to that of the first pass in the upper, after
recorded with a CsI detector that was placed on the middle of the lung field. The half-life resulting from the wash-out curve was 40 s, while the half-life obtained from the scintillation camera that was taking data simultaneously, turned out to be the equivalent value of 38 s.
3.2 . Animal test A probe with a single hole collimator (8 mm in diame-
ter) was used for testing a rat. 15 Mbq of
99mTc
MIBI
(which is equivalent dose to human) was injected intra-
venously into a rat after it being anesthetized with pentbar-
bital sodium . Then the probe was placed near the heart field. The time activity was measured, indicating that the radioactivity rises sharply, then falls quickly, and remains
constant for a long period . For 201 T1 chloride a similar time activity curve was obtained .
1400
v 'v
U
"
0 t~ 0 h
a
1400
U
ii Y
IJ J
0
°"f~nNU"JVf1
30 sec
0 0 u
30
sec Fig. 7. The upper curve shows the first pass radiocardiogram of LV after injection of 555 MBq of 99m Tc HSAD . The lower curve is the time activity curve, after injection of 185 MBq of the rest of 99mTc the HSAD.
Fig. 8. On the image, accumulations of 67 Ga citrate are clearly seen on both primary tumor and its lymphonode metastasis . The lower figure shows the distribution of counting rates (CPS) measured by the probe around region of the neck . VIIIa . BIOMEDICAL APPLICATIONS
456
M.Q. Makino et al. INucl. Instr. and Meth. t o Phys. Res. A 353 (1994) 453-456
injection of 185 MBq of the rest of
99'Tc
HSAD . This is a
typical first pass radiocardiogram of LV we have measured by a small EF probe. These data are obtained from a counting rate with 50 ms intervals, then later processed with a time sequence digital filter . 3.5 . Lymphoma In Fig. 8 the upper picture shows a tumor scintigraphy
of malignant lymphoma, right lingual tonsil of primary origin taken three days after injection of 111 MBq of 67Ga citrate. A swelling of right submandibular lymphonode
was observed . On the scinticamera image, accumulations
of 67Ga citrate are clearly seen on both primary tumor and its lymphonode metastasis . The lower figure shows the distribution of counting rates (CPS) measured by the probe around the region of the neck. Among them two higher
CPSs are observed, which correspond to the dense accu67 mulations of Ga citrate on the image.
4. Discussion For the above applications probes of 10 mm thickness of CsI(TI) crystal were used . The efficiency of the detector is rapidly decreased beyond the 200 keV of the incoming
gamma rays . The radionuclides used in the applications are 201 133 67Ga, and 81 ~Kr. Using the probes, TI, Xe, 99'Tc, emitting gamma rays from those nuclides are measured with sufficient detection efficiency .
The maximum wavelength emitted from CsI(Tl) is 540
nm [6] and the maximum sensitivity of the PIN photodiode used lies at 900 nm and its sensitivity is reduced to almost
one half at a wavelength of 540 nm [8]. The maximum noise level observed is around 30 keV at the room temperature.
5. Conclusion We have examined CsI(Tl) photodiode detectors re-
garding the energy resolution, the linearity of the detector,
and the efficiency for gamma ray, and we have shown
applications of the probes to biology and medicine .
CsI(Tl) miniature probes have characteristics of small
size and light weight with relatively higher efficiency for gamma rays, and yet they require no higher voltage. No housing, therefore, for voltage dividers is needed . Both CsI(TI) and photodiode are not expensive. The probes are rugged .
The CsI(Tl) probe is, however, not applicable for measurements requiring high energy resolution, but for rather biomedical applications, as we have shown, such as biological experiments using animals, radio immuno-guided surgery, localized measurements of time activity curves, and measurements of LVEF. The possible low energy limit for measuring gamma rays, therefore, seems to be around 50 keV.
References [11 D. Hunter, R. Lawrence, C. Morgan and T. Evans, Nucl . Med. Comm 11 (1990) 879. [2] P. Broadhurst, P Cashman, J. Crawley, E. Raftery and A. Lahiri, J. Nucl. Med. 43 (1991) 37 . [3] made by Horiba Ctystal Co ., Tokyo, Japan. [4] Manufactured by Hamamatu Photoelectronics, Hamamatu, Shizuoka, Japan. [5] C.M. Davisson and R.D. Evans, Rev . Mod. Phy. 81 (1951) 404. [6] K. Knoll, Radiation Detection and Measurement, 2nd ed . (Wiley, New York, 1979) p. 231. [7] R.D . Evans, The Atomic Nucleus (McGraw-Hill, New York, 1941) p. 717. [8] Photodiode specification sheets, Hamamatu Photoelectronics, Hamamatu, Shizuoka, Japan.