Functional aspects of anatomical imaging techniques

Nilendu Purandare Associate Professor & Consultant Radiologist Tata Memorial Centre

Anatomical imaging techniques

•Ultrasonography •CT scan •MRI

Functional/metabolic/molecular imaging (radioisotope scanning)

•PET •SPECT

Location Size/dimensions Density Morphology Spatial relations

Perfusion,flow Metabolsim (glucose, AA) Receptor expression Hypoxia,Apoptosis

Oncology / tumor imaging

Functional imaging Tumors •Metabolism (glucose, amino acid) •Proliferation •Hypoxia •Angiogenesis •Apoptosis •Image receptors

PET

Functional imaging Tumors •Metabolism (glucose, amino acid) •Proliferation •Hypoxia •Angiogenesis •Apoptosis •Image receptors

•Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

CT/MR

Tumor imaging

•Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

CT/MR

Angiogenesis (DCE MRI and CT Perfusion)

Physiological imaging (ultrafast imaging) Follows the early enhancement kinetics of contrast within first few minutes of IV bolus injection (TIC). Depicts tissue vascularisation, capillary permeability, perfusion, volume of interstitial space, thus indirectly tissue cellularity.

Angiogenesis (CT Perfusion) Assesses physiological parameters •Blood flow (BF) •Blood volume (BV) •Mean transit time (MTT) •Capillary permeability (CP/PS) In vivo markers of micro vessel density and angiogenesis

Angiogenesis (CT Perfusion)

•De-convolution based analysis technique •Operative derived ROI are placed on artery and representative portion of the tumor for input functions •Functional maps of perfusion parameters obtained

Angiogenesis (CT Perfusion)

Angiogenesis (CT Perfusion)

Rectal Cancer : response to neo-adjuvant therapy

MR Perfusion / DSC MRI (Brain tumors)

SI

Time

• Cerebral blood volume

• Cerebral blood flow

• Mean Transit Time

• Time to Peak

MR Perfusion / DSC MRI (Brain tumors)

• Establish the diagnosis of tumor

• Pre- operative assessment of tumor histology

• Guide tumor biopsy

• Assessment of true lesion extent

• Monitoring response to therapy (surrogate marker)

MR Perfusion / DSC MRI (Brain tumors)

Hyperperfusion

Possible glioma

Delineation of true tumor extent

Radiation Necrosis Vs tumor recurrence

Dynamic contrast enhanced (DCE) MRI • Tissue characterization (vascularity & perfusion) • Identifying viable areas to biopsy • Staging of local extent •Monitoring response to therapy (surrogate marker)

Angiogenesis (bone & soft tissue tumors)

(K-trans, tissue permeability)

Advanced techniques : DCE MR- Curve types

Advanced techniques : MRI •Dynamic contrast enhanced (DCE) MRI Tissue characterization

Highly perfused and vascularised tumor with small volume interstitial space Type IV curve-malignant

Advanced techniques : MRI •DCE MRI : Ideal site for biopsy

Highly vascularised , highly perfused viable portion of tumor (Synovial Sarc) Avoid edema, necrosis, normal tissue

Advanced techniques : MRI • DCE MRI : Surrogate marker of response to chemo Rx

MFH

Advanced techniques : MRI • DCE MRI : Residual/recurrent tumor from post Rx change

Gradual slope – pseudonodule Bx- negative for malignancy

Tumor imaging

•Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

Diffusion weighted imaging (DWI)

•Measures the motion of water molecules in the intra & extravascular spaces •Motion of water molecules is more restricted in tissues with high cellularity, intact cell membranes and reduced intracellular space •Malignant tumors in general have high cellularity and thus more restricted diffusion. •Quantitatively ADC values are used to study diffusion restriction

A B C

D E F

Diffusion weighted imaging (DWI)

Diffusion weighted imaging (DWI)

Diffusion weighted imaging (DWI)

Diffusion weighted imaging (DWI)

Synovial sarcoma –post surgery Enhancing nodule at surgery site ADC map- restricted diffusion Local recurrence

Tumor imaging

•Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

Metabolite quantification MR spectroscopy • Maps metabolite signal intensity from tissues (choline, creatinine, lipids, NAA, lactate, citrate) • Detects increased levels of choline • Marker of cell membrane turnover- feature of malignancy • Proton (H1) MR spectroscopy is used.

Normal Brain spectrum

Glioma spectrum

Radiation Necrosis Vs tumor recurrence

Metabolite quantification-MR spectroscopy

MR spectroscopy : Response evaluation Metabolite quantification

Tumor imaging

•Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

BOLD (Blood oxygen level dependant imaging)

•BOLD MR detects hypoxic subfraction and patients suitable for hypoxia modifying agents. •Provide a means of evaluating changes in tumor oxygenation in response to chemotherapy •Used for Brain, breast, pancreatic and prostate cancers

BOLD-MRI images are more likely to reflect on acute (perfusion-related) tissue hypoxia.

BOLD

Functional techniques Tumor imaging •Metabolism (glucose, amino acid) •Proliferation •Hypoxia •Angiogenesis •Apoptosis •Image receptors

•Size & Volume •Angiogenesis •Perfusion •Diffusion characteristics •Metabolite quantification •Hypoxia

PET

CT MRI

Neurology

Diffusion weighted imaging (DWI)

•Measures the motion of water molecules in the intra & extravascular spaces •Motion of water molecules is more restricted in tissues with high cellularity, intact cell membranes and reduced intracellular space • Infarcts show restricted diffusion in a few hours •Quantitatively ADC values are used to study diffusion restriction

Significance of penumbra

• Central irreversible infarcted tissue core

• Peripheral region of ischaemic but salvagable tissue called penumbra

Neurology

State of the art imaging of acute stroke

Mismatch

Comparison of Diffusion &

Perfusion Abnormalities

State of the art imaging

of acute stroke

Comparison of Diffusion &

Perfusion Abnormalities

Match

2 hours after deficit

7 days later

CBF MTT

3 hours

3 hours after deficit

7 days later

Penumbra is reversed after

endovascular clot retrieval &

revascularisation

Functional MRI ( F MRI)

BOLD

Functional MRI ( F MRI)

Defined cognitive task

Increased neuronal activity

Localized vasodilatation and

increase in blood flow

Signal response Increase in dimagnetic

oxyhemoglobin

Epilepsy: cortical dysplasia

Epilepsy: cortical dysplasia, fMRI

Cardiology

Cardiology MRI (Myocardial perfusion) use the “first pass” of an intravenously injected Gd contrast agent at rest and during administration of a vasodilator (i.e. adenosine ) to depict hemodynamically significant coronary artery stenosis

MRI (Cardiac Viability) Contrast enhanced CMR is a newly established technique for infarct assessment. Regions of myocardial infarction exhibit high signal intensity (contrast enhancement) on T1‐weighted images after administration of contrast such as gadolinium based agents.

Top panel:

Subendocardial infarct, prominent perfusion defects larger than infarct on stress MR

Bottom panel:

Matched stress and rest defects, no infarction, CA is normal- artifactual

MR Perfusion

MRI: Viability

58 yrs old man (EF-20%) Dilated cardiomyopathy Thinning of inferior wall on still images Late ce- MRI shows transmural enhancement suggesting old MI

In chronic CAD patients, myocardial enhancement in areas of dysfunctional myocardium corresponds closely to fixed defects on thallium SPECT, and areas of flow-metabolism matched defects on FDG-PET scans, histologically representing scarred or fibrotic tissue

Color Doppler Ultrasound

Estimates blood flow and velocity Locate and grade vascular stenosis

2D echo Pumping function (ejection fraction)

Summary

CT/MRI (DCE MRI, DWI, spectroscopy, BOLD)

•Oncology Angiogenesis (perfusion), diffusion, metabolites, hypoxia

•Neurology Functional maps, CBF,CBV, MTT (epilepsy, stroke)

•Cardiology Myocardial perfusion, viability

Thank you