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Joseph V. Fritz, PhDNandor Pintor, MDDent Neurologic InstituteASN 2017Friday, January 20, 2017

� Siemens Medical Systems

� Research Agreement

� Philips Healthcare

� Research Agreement

� AAN and ASN Committees

MRI� Internal source (protons)

encode soft tissue character

� Tomographic Acquisition any Plane

� 3 Tesla, 80 mT/m, 200 T/m/s,min TR, min TE

� 4 W/kg, Magnetic force

CT� External source (x-ray)

encode tissue density

� Tomographic Acquisition Axial Plan, MPR any Plane

� 320 slice @ 0.5mm, 250ms rotation, dose reduction

� 3 milliSieverts nature50 mSv annual limit

� CT

� Keep Dose Similar to Background

� Reformating

� Dynamic / Functional Imaging

� Tissue Characterization

Single Rotation for Full Volume (16cm)

Multi-Spectral

� MRI

� Speed

� Artifact Reduction

� Functional and Metabolic Imaging

Field Strength (SNR, Speed, Resolution)

Parallel Receive and Transmit

MRI� Contrast or Non-Contrast

� 0.5 x 0.5 x 1 mm3

� Flow and Metal Artifacts

� Minutes

� Advances in fast dynamics, functional, artifact reduction

CT� Contrast (+pre if subtraction)

� 0.5 x 0.5 x 0.5 mm3

� Stent/Ca artifacts

� Seconds

� Advances in bone removal, dynamics

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Radio/TV

Visible

Microwaves

Xray

http://www.hardhack.org.au/xraydtt

Harder beam,More penetration

J. Nucl. Med. Technol. March 1, 2005 vol 33 no. 1 3-18

Photoelectric Dominates Soft

Tissue Attenuation

Compton Dominates Dense

Material Attenuation (Bone, Iodine)

� Stretch the Slinky

� Faster, less dose

� Blurred slices

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FoV / Matrix (eg 0.5mm in Brain)

Detector

Dimension

4 cm 8 cm 16 cm

Single Rotation

64 detector row CT coverage

Single Rotation

160 detector row CT coverage

Single Rotation

320 detector row CT coverage

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ReviewTissue HU

Air -1000

Lung -500

Fat -100 to -50

Water 0

CSF +15

Blood +30 to + 45

Muscle +1- to +40

Grey Matter +37 to +45

White Matter +20 to +30

Soft Tissue, Contrast +100 to +300

Bone +700 (Cancerous) to +3000 (dense bone)

125 mAs 200 mAs

� CT Dose Index: Radiation from the Tube (CTDI, in mGy)

� Increases with Current (mA), time (s, mA*s), Voltage (kV)

� Need less if Detector more sensitive, less overlap, etc

� Dose-Length Product (DLP, in mGy*cm)

� Total Amount of Radiation The Body

� Multiply Dose times Coverage in cm

� Effective Dose on a Person in milliSieverts (mSv)

� Amount of Radiation Absorbed (IT IS CUMULATIVE)

� Multiply DLP/1000 by “k-factor” (2.2 in head, 5 in neck, 15 in body)

� eg Background < 3 mSv; Professionals < 50 mSv / Year

Peds: 2-5x more

Exam Effective Body Dose

(mSv)

Absorbed Organ Dose

(mGy)

Annual Background* 2.4 2.4

Chest x-ray 0.02 0.01 – 0.15

Head CT 1 – 2 56

Screening Mammo 0.4 3

Abdomen CT 8 14

Chest CT 5 – 7 13

CT Colonography 6 – 11

Chest-Ab-Pelv CT 9.9 12

Cardiac CT 9 – 12 400– 100

Barium enema 15 15

Neonatal Abdominal CT 20 20

*99% less than 7 mSv per year

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Innovations in Reconstruction

Detector

Material

1995 2000 2005 2010 2015

Filtering

4 slice

Tube Modulation

Filtering

16 Slice

New Recon Methods

64 Slice

ECG Modulation

256 Slice

Iterative Reconstruction

320 Slice,

Active Collimation,

Recon

Do

se

Dynamic

Scan Mode

Collimation Pitch kVp mARotation

TimeScan

RangeCTDImGy

DLPmGy.cm

Effective Dose

K

Volume 0.5mm x 240 NA 135 250 0.75s 120mm 44.7 571.9 1.2 mSv 0.0021

With Iterative ReconWithout

CTDImGy

DLPmGy.cm

Effective Dose

K

44.7 571.9 1.2 mSv 0.0021

CTDImGy

DLPmGy.cm

Effective Dose

K

70.0 1119.7 2.35 mSv 0.0021

(31% ↓ dose compared to helical acquisition)

Courtesy of Dr. Greenberg,

Arkansas Children’s Hospital

Accessory Occipital Suture

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� In direction of greatest attenuation

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Temporal uniformity,

no table movement

No temporal uniformity,

rapid table movement

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Scan Mode

Collimation Pitch kVp mARotation

TimeScan

RangeCTDImGy

DLPmGy.cm

Effective Dose

K

Dynamic 0.5mm x 320 * 80 mA boost 0.5 160mm 138 2206.3 4.6 mSv 0.0021

rCBV rCBF MTT

CBF = CBVMTT

Courtesy Erin Angel, Toshiba

CBV = Autoregulation

CBF = Low Flow

MTT = vasodilation

TTP, Delay = Stenosis, Colateralization

� Tissue at risk: relative MTT

� optimal threshold of 145%

� Infarct core: absolute CBV

� optimal threshold 2.0 ml/100g

Wintermark, Stroke. 2006; 37: 979-985

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� Differentiate Bone,

Contrast� CTA without bone

removal

� Eliminate Calcification Artifact

� Metal Artifact

Reduction� Plaque

Characterization

Ratio of

Detected HUs

*AN Primak, et al, AJR:195, Nov 2010

(RITRadiology.com)

� Isotropic Voxels (Image in Any Plane)

� Wide detector array � 320 x 0.5mm (640 x 0.25mm)

� Dose Reduction Methods

� Faster Imaging� Fast Gantry Rotation (0.25 s)

� Multiple X-ray Tubes

� Dynamic Imaging. Functional Assessment. Angio/Perfusion

� Artifact Reduction� Multi-Energy