Purpose. Head and Neck Imaging. Head and Neck Imaging. Advances in Head and Neck Imaging PET. Review imaging techniques of head and neck imaging

Purpose Advances in Head and Neck Imaging  Review imaging techniques of head and neck imaging Colin S. Poon, MD, PhD, FRCPC Adjunct Assistant Prof...
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Purpose

Advances in Head and Neck Imaging

 Review imaging techniques of

head and neck imaging Colin S. Poon, MD, PhD, FRCPC Adjunct Assistant Professor of Radiology

 Case examples

Yale University School of Medicine U.S.A.

Head and Neck Imaging   Skull base   Extracranial neck   Temporal bones   Temporomandibular joints   Pharynx / Larynx   Cranial nerves   Brachial plexus   Vessels

Head and Neck Imaging  CT  MR  PET

CT

CT Neck

  Preferred technique for extracranial

structures in most institutions

  Accessible   Less prone to motion   Patient motion (sick patient)   Physiological motion (swallowing,

breathing)   High spatial resolution   Good contrast resolution

Importance of Multiplanar Reformats

  Head and neck anatomy are complex

and pathology may be subtle   Lesions may not be equally apparent

on all imaging planes.  Multiplanar reformats are important for

head and neck imaging.  Most useful planes are axial and coronal.

Puff Cheek Technique

45 year old male, adenocarcinoma of the hard palate

The lesion is easy to miss on axial images, but ismore obvious on the coronal reformatted images.

CT images with standard technique shows no obvious abnormality

CT images with “puffed cheek” technique, shows a buccal adenoid cystic carcinoma

Dual Energy CT

Dual Energy CT

Dual energy CT correctly disproves false positive laryngeal cartilage invasion.

Conventional CT

Dual Energy CT Kuno H, et al. Radiology 2012; 265: 488-496

55 year old Chinese man with conductive hearing loss

Dual energy CT correctly diagnose true positive laryngeal cartilage invasion.

Conventional CT

Dual Energy CT Kuno H, et al. Radiology 2012; 265: 488-496

Nasopharyngeal Carcinoma with Intracranial Extension

MRI for Head and Neck   Superior soft tissue contrast  Helps to detect subtle mucosal

abnormality  Important for evaluation of skull base and cranial nerve lesion

MRI   Best for imaging soft tissues, nerves   Imaging protocol   Thin sections (≤ 3 mm)   Axial and coronal planes   T1 and T2 weighting   Includes post-gadolinium imaging   To fat-suppress or NOT to fat-suppress, this is the controversy   Air – bone – soft tissue interface results in severe

magnetic susceptibility that can lead to failure in fat suppression and image artifacts

T2W fat-sat

Contrast enhancement is not necessary for diagnosis if reliable fat suppression is available.

Glomus vagale - with extension into jugular foramen and cerebellopontine angle

Post-Gadolinium

Brachial plexus

Reliable Fat Suppresion is Important for Head and Neck Imaging

      

  

Applications of FatSuppression  Head and neck imaging

The Basic MR Physics

 Brachial plexus

Protons are like small magnets precessing along axis of main magnetic field

Fat and water have different precessing frequencies

T1 and T2 Relaxation

Fat has much short T1 relaxation time than water

Downloaded from: Clinical Magnetic Resonance Imaging, 3rd edition (on 24 July 2007 12:23 AM) © 2007 Elsevier

Fat and Water Has Different Resonant Frequencies

Fat Suppression

STIR

Chemical Selective Presaturation

Chemically Selective Presaturation Pros

Cons

  Versatile

Challenge of Effective Fat Suppression

  Magnetic field inhomogeneity

  Sensitive to B0 and B1

inhomogeneity

  Relative fast   Applicable to most pulse

  Low sequence efficiency

sequences

 Static magnetic field = B0   Leads to off resonance effect  Radiofrequency magnetic field = B1   Leads to non-uniform RF power

SPAIR

SPAIR

Spectrally Adiabatic Inversion Recovery   Spectrally = select fat only   Adiabatic = special RF pulse insensitive to B1

inhomogeneity   Inversion Recovery = null fat signal

Limitation: Does not solve the problem of B0 inhomogeneity

T2W

T2W SPAIR

Targeted Shimming Targeted Shimming No targeted shimming

Targeted shimming Targeted Shimming Volume

SPAIR After Targeted Shimming

Radiofrequency Energy Tips Magnetization Away From Longitudinal Axis of Main Magnetic Field Non-uniform RF power will lead to variation in fat saturation

Effect of B0 and B1 Inhomogeneity on Chemical Selective Fat Saturation Pulses A.  Normal fat saturation

B.  B0 inhomogeneity results in

incomplete fat suppression

C.  B0 inhomgejeneity results in

inadvertent water suppression

B.  B1 inhomogeneity results in

incomplete fat suppression

Fat Suppression

Inversion Recovery

STIR

Chemically Selective Presaturation

STIR

STIR Pros   Robust to B0 and B1

inhomogeneities   Reliable fat suppression

Cons   Mixed constrast   Inherent T1 weighting

  Only works with proton

density and T2W   Low SNR efficiency   Suppresses short T1 species

and enhancing tissue after contrast Inversion of Magnetization

Wait until fat signal goes through null point

Chemically Selective Fat-Sat vs. STIR

Comparison of short inversion time inversion recovery (STIR) and fat-saturated (chemsat) techniques for background fat intensity suppression in cervical and thoracic MR imaging Nakatsu M. , et al. J. Magn. Reson. Imaging

2000; 11:56-60

  Five-point rank score analyses were utilized by

Chem Fat-Sat

three experienced radiologists. The mean scores of STIR and fat-saturated FSE techniques for uniformity of fat suppression were 4.3 and 2.3, respectively (P < 0.0001). The mean scores of STIR and fat-saturated FSE techniques for lesion conspicuity were 4.2 and 3.5, respectively (P < 0.0001).

STIR

STIR vs. Chemical Saturation J. Magn. Reson. Imaging

STIR

Uniformity of Fat Suppression

2000; 11:56-60

Chem Sat FSE T2

FSE T2

Score

STIR FSE

Fat-saturated FSE

5 

18

4

16

3

5

2 

1

1 

0

11

Total

40

40

Mean

4.3

2.3



0 7 



7 15

Lesion Conspicuity Score

STIR FSE

5 

17



3

4 

10



20

3 

7

10

2

1

1

1

0



1

35



35

Total Mean



Fat-saturated FSE

4.2

Chemical Shift Based WaterFat Separation Dixon Technique and Variations

3.5

Original Dixon Technique

Original Two Point Dixon Technique   Sensitive to B0 inhomogeneity

Solution:   In-phase = Water + Fat   Out-of-phase = Water – Fat

Map the magnetic field inhomogeneity by acquiring additional points and applying correction in reconstruction

  In-phase + Out-of-phase = Water only   In-phase – Out-of-phase = Fat only

=> Three-point or four-point Dixon

T1  and T2weighted fast spinecho imaging of the brachial plexus and cervical spine with IDEAL water–fat separation

IDEAL Iterative Decomposition of Water and Fat with Echo Asymmetry and Least Squares Estimation

Recombined

Water

Fat

CHESS-FSE

IDEAL

Journal of Magnetic Resonance Imaging Volume 24, Issue 4, pages 825-832, 12 SEP 2006 DOI: 10.1002/jmri.20721 http://onlinelibrary.wiley.com/doi/10.1002/jmri.20721/full#fig1

Fat Suppression Techniques

Chemical Shift Water-Fat Separation Pros   Robust to B0 and B1

inhomogeneities

  Reliable fat suppression

  Provides fat and water

Cons   Long scan times   More complex

reconstruction

Chem Fat-Sat

Method

Pros

Cons

Applications

Chemically selective fat suppression

• Relatively fast • Applicable to most pulse sequence

• Sensitive to B0 and B1 inhomogeneities

Poor performance for head and neck, brachial plexus

Spatial-spectral pulses

• Insensitive to B1 inhomogeneities

• Sensitive to B0 inhomogeneities

STIR

• Insensitive to B0 and B1 inhomogeneities • Reliable

• Poor SNR • Mixed contrast • Inherent T1 weighting

Chemical shift based water-fat separation (Dixon methods)

• Reliable • Corrects for chemical shift • Universal compatibility • High SNR

• Long scan time • More complex reconstruction

images   Allows recombined images   Corrects for chemical shift   High SNR efficiency   Allows quantitative

applications

Choice of Fat Suppression Methods

Applications

Chemically Selective Presaturation

General purpose. Quick and easy.

SPAIR

When B1 inhomogeneity expected.

STIR

Large FOV Inhomogeneous B0 Need reliable fat suppression

IDEAL

All application requiring robust fat / water separation. Scan time not an issue

High Resolution Heavily-T2 Weighted 3D Sequence

CN XII - Hypoglossal

Sheth, S. et al. Radiographics 2009;29:1045-1055

Obstructive Sleep Apnea

Diffusion Weighted Imaging for Cholesteatoma

Macroglossia (unusual size) and glossoptosis (unusual location) can lead to obstructive sleep apnea.

Cine MRI study using fast gradient echo technique

Obstruction of the oropharynx when the tongue moves posteriorly (middle image) during sleeping Schwartz KM, et al. AJNR 2011; 32: 430-436

Comparison of Diffusion Imaging Techniques for Cholesteatoma SS TSE (HASTE) DWI

EPI-DWI

Multishot TSE DWI (BLADE)

PET/CT

Multishot TSE DWI (BLADE)

PET/CT

PET / MR ?



Squamous cell carcinoma of oral tongue with metastatic lymphadenopathy

The End