Vicente Herrero* , Christoph W. Lerche Michelle Spaggiari , Ramón Aliaga,

AMIC: AN EXPANDABLE FRONT-END AMIC: AN EXPANDABLE FRONT-END FOR GAMMA-RAY DETECTORS WITH FOR GAMMA-RAY DETECTORS WITH

LIGHT DISTRIBUTION ANALYSIS LIGHT DISTRIBUTION ANALYSIS CAPABILITIESCAPABILITIES

Vicente Herrero* , Christoph W. Lerche

Michelle Spaggiari, Ramón Aliaga,

Néstor Ferrando and Ricardo Colom.

17th REAL TIME CONFERENCE / IEEE - NPSS

ContinuousContinuous ScintillatorScintillator RayRay DetectorDetector

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q

Lower cost.

Higher detector sensibility. [1]

Better energy resolution. [2]

Light Distribution Analysis [3][4]

Geometry and Coating can be changed for optimization. [5]

[3] C. W. Lerche, et al. “Depth of gamma-ray interaction within continuous crystals from the width of its scintillation light-distribution” IEEE Trans. Nucl. Sci., (52), 560, 2005.

Designed for PET applicationsLSO : 42x42x10 mm

PMT : Hamamatsu H8500

[2] P. Bruyndonckx, et al. “Initial Characterization of a Nonpixelated Scintillator Detector in a PET Prototype Demonstrator”, IEEE Trans. Nucl. Sci., (53), 2543, 2006.

[1] P. Bruyndonckx, et al. “Performance Study of a PET Detector Module Based on a Continuous Scintillator”, IEEE Trans. Nucl. Sci., (53), 2536, 2006.

[5] C. W. Lerche, et al. “Dependency of Energy, Position and Depth of Interaction on Scintillation Crystal Coating and Geometry", IEEE Trans. Nucl. Sci., 55, (2008) 1344.

[4] C. W. Lerche, et al. “Fast circuit topology for spatial signal distribution analysis and its application to nuclear medicine imaging” IEEE NPSS RT 2010,


PESICPrevious WorkPrevious Work

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◦ Individual Anode Gain Adjustment for Detector Equalization [7]

◦ Reduces error due to signal delay in resistor network [6]

◦ Not an expandable architecture

◦ Low resolution in Depth of Interaction (DOI) measurements [7]

[7] V. Herrero, et al. “Position sensitive scintillator based detector improvements by means of an integrated frontend”, NIMA., (604), 77, 2009.

[6] V. Herrero, et al. “PESIC: an integrated front-end for PET applications”, IEEE TNS., (55), 27, 2008.


Mathematical Foundations of Mathematical Foundations of AMICAMIC

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Moment n of distribution f(x)

ENERGY

CENTROID (x AXIS)VARIANCE (width of distribution)

xxfxm xx )(1

xxfm xx )()1(0

xxfxm xx )(22

xxfxm xx )(33SKEWNESS (assymetry of distribution)

… …

DISCRETIZED

BASICOPERATION

fx(0)

fx(1)

fx(2)

fx(3)

Kn(x)

Kn(0)

Kn(1)

Kn(2)

Kn(3)

+nxm



AMIC ArchitectureAMIC Architecture

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64 input buffers

8 Computational Blocks

8 Output Amplifiers (current & voltage)

64 light distribution samples

I2C interface (coef.

program.)


Preamplifiers and Output Preamplifiers and Output StageStage

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Both SiPM and PMT capable

Optimized PMT Bandwidth > 34 MHz Noise 0.1 uArms

Mismatch in current mirror between different preamps

Solved by calibration of coeff. values

40ux100u

175u x135u

Current Output Voltage Output using

an R amplifier Bandwidth > 20 MHz SlewRate = 350 V/us

(CL= 50pF)

THD < 0.35 % (0.5mApp)


Computational BlockComputational Block

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1540u x120u

Analog Current Mode Filter

40u x50u

Coefficient values < 1 with 8 bits precision offers 256 different values for coefficients. A linear distribution (M1) of 28 values on one

axis means 256x256 inputs 64*8=512 Coefficient units !! Area needs

to be restricted

[5] K. Bult and G. Geelen “An inherently linear and compact most-only current division technique", 39th IEEE-ISSCC 189 (1992).

Extremely sensitive to Vout = Vdump◦ Small differences introduce big linearity errors

Area ratio optimized for a maximum input current of 6mA (BW > 60 MHz)

Needs biasing to get a better linearity

Vout=Vdump

Coefficient Unit


Computational BlockComputational Block

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Necessary to stabilize DUMP & OUT voltages to the same value

High bandwidth (>200 MHz), PM (>80º) and Low THD (<0.05 %)

Matched layout needed for DUMP & OUT current paths◦ Differences in parasitic resistance introduce voltage

variations in DUMP & OUT voltages close to coeff.

◦ 1 collector handles 16 coeff.

Fully Differential Current Collector

200u x50u


Architecture Expansion using Architecture Expansion using AMICAMIC

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AMIC is the basic building block

Each AMIC generates up to 8 «partial moments»

1 AMIC is enough to implement the final addition of all «partial moments» (up to 64 «partial moments» of 64 inputs which means 4096 inputs !!)

Anyway if you need more… just add more AMICs at the output◦ Only noise generated in the front-end

limits the number of inputs

AMIC 1

AMIC II

AMIC III

AMIC IV

AMIC V

8x

8x

8x

8x

8x


Performance Test Performance Test MeasurementsMeasurements

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0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Coefficient Code

Nor

mal

ized

Val

ue

y(x) = a (x - b)a = 0.0039294b = 3.0374R = 0.99991 (lin)

Linearity of Coefficient Values

Most codes lie inside the limits but… 7 effective bits

Area constrains in Coeff. Unit introduce mismatch

Bandwidth 16 MHz

Linearity vs. Input Current

(Coeff. Value =128)

± 0.65 %

Input Dynamic Range

(within Linearity limits)

1.65 mA

THD 0.5 mA / 100kHz

0.5%

Noise (current output)

1.8 µArms

Switch matrix made with 8 ADG2128 (Analog Devices)


Experimental Setup Test Experimental Setup Test MeasurementsMeasurements

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5x5 Sweep on detector surface

(6 mm steps)



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AMIC calibrated for preamp mismatch compensation

Collimation Spot = 1 mm M1x & M1y OUTPUTs (same

results)

No improvements made by adding information of other moments

As usual border effect increases resolution far from center

Just testing everything works

M1x calibrated coefficients



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AMIC calibrated for preamp mismatch compensation

«Non invasive» method DOI can improve 2D position

resolution and also reduce parallax error after reconstruction stage

Improvement of 300% over previous results with PESIC

M2 calibrated coefficients

of light

distribution Depth of Interaction

[3] C. W. Lerche, et al. “Depth of gamma-ray interaction within continuous crystals from the width of its scintillation light-distribution” IEEE Trans. Nucl. Sci., (52), 560, 2005.

[3]

+++

[7] V. Herrero, et al. “Position sensitive scintillator based detector improvements by means of an integrated frontend”, NIMA., (604), 77, 2009.


The higher the number of inputs the better the spatial resolution… but also:

2D position calculation can be improved by using other moments information

DOI calculation can also be improved the same way

NOW WORKING WITH NEURAL NETWORKS to optimize full reconstruction of detected events

This is just the beginning…This is just the beginning…

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A lot of information waiting A lot of information waiting there to be used …there to be used …

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Check out Christoph W. Lerche’s work at the poster session !!!!



We also work on:

◦Increasing Timing resolution in Coincidence Detection J. M. Monzó

◦High Performance Data Acquisition Systems R. Aliaga

Other work being carried Other work being carried out…out…

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THANK YOU FOR THANK YOU FOR YOUR ATTENTIONYOUR ATTENTION

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Vicente Herrero* , Christoph W. Lerche Michelle Spaggiari , Ramón Aliaga,

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