CT VS MRI PERFUSSION

BASIC PRINCIPLE

Purwanto

Workshop Radiografi Munas Pari Lombok

, 8-10 November 2019

Unrestricted

TOPIC MATERI

• Introduction

• Basic principle CT & MRI

• CT Perfusion

• MRI Perfusion

Introduction

• CT or MRI imaging information is limited

to anatomical morphology

• Certain conditions need additional

information

• One additional information for therapeutic

purposes is blood flow information

Introduction

Introduction

Introduction

Introduction

Introduction

Arterial phase Venous phase Equilibrium phase Contrast injection

0 15 30

artery

75 120

Time (s)

MULTI-PHASE LIVER

Basic principle CT & MRI

Tissue

-Anatomy

-Physiology

-Biochemistry

-Pathology

μ (radiation absorbtion)

Signal Intensity

Basic principle CT & MRI

Tissue

-Anatomy

-Physiology

-Biochemistry

-Pathology

Image parameter

MRI Proton density

T1

T2/T2*

Flow

Chimical shif

Susceptibility

Diffusse

Perfusion

RF absorbtion

Signal

Intensity

Pulsa SequenceSpin echo

Gradien echo

Invers recovery

dll

CT Perfusion

• Perfusion is the process of passage of blood

from an arterial supply to venous drainage

through the microcirculation (capillary bed).

• It is a fundamental biological function that

refers to the delivery of oxygen and nutrients

to tissue by means of blood flow.

• Perfusion normally refers to the delivery of

blood at the level of capillaries and measures

in ml/100gm/mi

CT Perfusion

. Model Johnson dan Wilson distribusi kontras media intravena dalamtumor.nKonsentrasi terlarut dalam ruang intravaskular (darah), Cb (x, t),

tergantung pada posisi sepanjang kapiler, untuk mencerminkan bahwa iamenurun dari arteri (Ca (t)) ke ujung vena (Cv (t)). kapiler. Ruang interstitial diasumsikan sebagai kompartemen tanpa gradien konsentrasi di dalamnya

CT Perfusion

• Blood Flow: Volume of blood moving through a given volume of tissue per unit time (ml /100g/min)

• • Blood volume : Volume of flowing blood within a vasculature in tissue region (ml per 100 g)

• • Mean transit time : Average time taken to travel from artery to vein (Seconds)

• Time to peak enhancement: Time from the beginning of contrast material injection to the maximum concentration of contras

MRI Perfusion

• Measurement of perfusion requires the

use of tracers -- molecules, molecular

aggregates, or small particles that

distribute in tissues commensurate with

blood flow and can be detected

MRI Perfusion

• Intravascular tracers remain confined to blood vessels.

• Extracellular tracers do not enter cells but freely pass through vessel walls to distribute in the extracellular spaces of tissues. Most gadolinium-based contrast agents are in this category

• .Diffusible tracers distribute throughout all tissue compartments including the interior of cells. A common example in MRI is magnetically tagged water molecules used for arterial spin labelling(ASL).

Dynamic Susceptibility Contrast (DSC)

Perfusion MRI

• DSC perfusion imaging begins with a

bolus of gadolinium chelate

injected intravenously, followed by a series

of rapidly acquired gradient or spin echo

images over the organ of interest

• As the gadolinium first passes through the

regional circulation, it remains largely

confined to the intravascular space

Dynamic Susceptibility Contrast

(DSC) Perfusion MRI

• By measuring signal intensity as a function of time and fitting to a mathematical model, various perfusion parameters (e.g., blood volume, blood flow, mean transit time) can be extracted.

• Because DSC imaging depends only on the first pass of the contrast agent, it is sometimes known as bolus tracking MRI. Image acquisition time is therefore very short (~2 min).

Dynamic Contrast Enhanced (DCE)

Perfusion MRI

• DSC imaging, DCE also requires

exogenous administration of a gadolinium-

based contrast agent. DCE, however,

exploits the T1 shortening effects of

gadolinium, acquiring repeated T1-

weighted images over an approximately 5

-10 minute interval

Arterial Spin Labeling (ASL)

• Unlike DSC and DCE perfusion MRI, ASL does not require the administration of gadolinium contrast. Instead, the patient's own water molecules serve as an endogenous diffusible tracer.

• This is accomplished by "magnetically labeling" water molecules in proximal blood vessels with radiofrequency pulses.

• As these molecules flow into the organ of interest they reduce tissue signal intensity in proportion to perfusion.

• In the typical ASL pulse sequence, images are acquired both with and without labeling pulses, then subtracted. By applying a mathematical model, various perfusion parameters (principally blood flow) can be obtained.