Specialist Modalities Applications

Safety concerns of a Static Magnetic Field

Static Magnetic Field- projectile of metals/pulled force of metal, must remove metallic things (jewellery etc)

Need consent and safety forms

Safety concerns of Radiofrequency pulse

Radiofrequency Pulse can:

Produce heat and create burns if there is a closed circuit in the body

Produce Peripheral Nerve Stimulation

Safety concerns of Gradient Coils

They vibrate loud so can damage hearing

Patients require earplugs

MRI Zone 4

Zone 4: Magnet Room

Authorised access only

The scan room door is always locked when unattended

Metal is removed

Danger signs

When the scan room door is opened, the MRI Safety barrier must be implemented at all times by MRI personnel

Forms for safety and consent

MRI Zone 3

Zone 3: Control Room

All metal removed

Locks on doors

Caution signs

Authorised access only

MRI Zone 2

Zone 2: Patient Screening and Prep

Patients and families undergo screening and are cleared to enter the magnetic area

MRI Zone 1

Zone 1: Unrestricted area (public walkway)

Time of Flight (TOF) applications

A specialised imaging technique of visualising blood vessels without contrast

Applications:

TOF MRA is commonly used to diagnose conditions like intracranial occlusions, aneurysms, and arteriovenous malformations

In plane Imaging

In-Plane Imaging is where the MRI is parallel to the flow direction allowing the image to be bright.

This is because we are still in the FoV so get signal

Applications:

In plane imaging offers the potential for assessing vessel patency, and both volume flow rate and flow velocity

Through plane Imaging

Through Plane Imaging is where the imaging is perpendicular to the flow direction making the image dark.

This is because the atom we gave the signal to has now left/gone past the fov

Applications:

Used for quantitative flow measurements, such as volume flow rate and velocity

1.5 Tesla Imaging Method

1.5 T imaging uses a magnetic field strength of 1.5 Tesla. It is used for routine, whole-body imaging and is found in public hospitals:

Pros

• is more tolerable for sick patients

• less movement artefacts

• safer

3 Tesla Imaging Method

3 T Imaging uses a magnetic field strength of 3 Tesla and is high resolution imaging.

Pros

• has more signal

• decreased scan time

Cons

• More chance of burns and projectiles

• Harder for patients to thermoregulate so increased movement

T1 Weighted Imaging

T1 is typically used as an informal anatomy scan.

• Fat is Bright (quickly realigns its longitudinal magnetisation with B₀)

• Water is Dark (has much slower longitudinal magnetisation realignment after an RF pulse and therefore, has less transverse magnetisation)

Applications:

• T1 focuses on highlighting anatomy

• Useful to detect contrast

• As contrast media goes to areas of high blood supply it can detect infections

T2 Weighted Imaging

T2 is good for detecting pathologies such as cysts

• Water is bright

• Fat is grey

Applications:

T2 focuses on pathology, making fluids bright, which is ideal for visualizing inflammation, edema, and certain lesions

T2 Fat Saturation

T2 Fat Saturation is used to see inflammation. This technique “turns off” or removes any fat from the image so now:

• Fluid is bright

• Bone is dark

• Fat is dark

Applications:

Enhance the visualization of specific tissues or structures by suppressing the signal from fat

Advantages of Ultrasound

Advantages

• Readily available

• Relatively cost effective

• Does not use ionising radiation

• No contraindications

• Shorter scan and wait times compared to MRI

• Can be dynamic and interventional

• Scan can be easily extended to assess other areas

• Non-invasive

• Minimal patient prep

• Mobile

• Dynamic info

• Excellent solid vs cystic info

Ultrasound Disadvantages

Disadvantages

• Operator Dependence - training of sonographer and experience may yield varying results

• Artefact misinterpretation

• Thermal/mechanical injury (fetus most at risk- no known effects)

• Limitations: bone, air or unfavourable body habitus

• User injury

• Little physiological info

• Reproducibility between scans

• Benign vs Malignant cross-over appearances

Complex Cyst Appearances

• Thick walled

• Internal echoes

• Septations

• Internal Flow

• Irregular Outline

• solid and cystic

• Mural Nodules

Right Upper Quadrant Pain (Biliary Stones) Symptoms

• Complaining of RUQ pain (sometimes colicky)

• Onset of pain after fatty food

• Nausea/vomiting

• Bloating

• Murphys positive

• Jaundice

RUQ Pain Differentials

• Hepatitis or other liver disease

• Pancreatitis

• Cholecystitis

• Choledocolithiasis

• Sphincter of Oddi dysfunction

• Vascular Compromise- eg portal vein thrombosis (patient usually is unstable)

X-ray use for US

An erect cxr is used to rule out plural causes or abdominal air

Abdoment xr to rule out obstruction - occasionally a large biliary stone can be found

Cholecystitis on US

• Thick Gallbladder walls

• Oedematous wall (swollen)

• Vascular wall

• Murphys positive (hand pressed on gallbladder area produces pain on inspiration)

• Fluid surrounding Gallbladder

• Stones in Gallbladder

• Contracted gallbladder

• Wall Echo Sound sign (contracted gall bladder filled with stones)

Choledocholithiasis on Ultrasound

Choledocholithiasis

• Bile duct >6mm

• Intrahepatic duct dilatation

• Distended Gallbladder

• +/- pancreatic duct dilation

• Stones in gallbladder

Ultrasound vs ERCP Advantages

US Advantages

• Non-invasive

• Assessment of organs/complications or other causes of pain - assess Gallbladder as well as the Bile Duct and mobility of stones in the gall bladder

• Readily available, cost effective etc

• May lead to surgical intervention earlier for:

Cholecystitis (to OT for Lap Chole)

Choledocholithiasis (if confirmed on US then to ERCP, if not confirmed on US then to MRCP)

No stones seen but ductal dilatation intra and extrahepatic (to CT for ?mass or MRCP)

US vs ERCP Disadvantages

US Disadvantages

• Limitations due to gas, habitus and (sometimes) pain - can see distal obstruction signs but not the cause

• Operator Dependent

• No Intervention available at the time of scan

ERCP vs US Advantages

ERCP Advantages

• Higher sensitivity for Choledocholithiasis

• Interventions available at time

• Sphincterotome can be performed for further stones to come through

• Avoids full anaesthetic in comparison to IOC/Lap Chole

ERCP vs US Disadvantages

ERCP Disadvantages

• Invasive

• Ionising Radiation

• Sedation required

• Risk of perforation

• Risk of pancreatitis

• Painful

• Reduced Pt compliance/consent

US vs MRCP Advantages

US Advantages

• Non-invasive

• Assessment of organs/complications or other causes of pain - assess Gallbladder as well as the Bile Duct and mobility of stones in the gall bladder

• Readily available, cost effective etc

• May lead to surgical intervention earlier for:

Cholecystitis (to OT for Lap Chole)

Cholecystitis and Common Bile Duct Dilatation may have Intra Operative Cholangiography and Lap chole

Choledocholithiasis (if confirmed on US then to ERCP, if not confirmed on US then to MRCP)

No stones seen but ductal dilatation intra and extrahepatic (to CT for ?mass or MRCP)

US vs MRCP Disadvantages

US Disadvantages

• Limitations due to gas, habitus and (sometimes) pain - can see distal obstruction signs but not the cause

• Operator Dependent

• No Intervention available at the time of scan

MRCP vs US Advantages

MRCP Advantages

• Detailed anatomy - can detect head of pancreas mass and for cholecystitis

• Higher sensitivity for Choledocholithiasis

• Not limited by gas, bone or most habitus

• No ionising radiation

MRCP vs US Disadvantages

MRCP Disadvantages

• Expensive

• High demand modality - long wait times

• Claustrophobia - reduced patient compliance

• Does not assess mobility of gallbladder stones

• Non-interventional

Advantages of US vs CT for Right Right Iliac Pain

US Advantages

• US is non-ionising

• Dynamic assessment

• Readily available

• Female - rule out ovary involvement

• Male - may proceed to CT sooner

Disadvantages of US vs CT for Right Iliac Fossa pain

Disadvantages of US

• US limitation of gas and mid ureter

• Sonographer may not be onsite (overnight)

Functional Imaging Nuc Med

Functional Imaging= uses radioactive tracers (radiopharmaceuticals) to visualize and assess the physiological functions of organs and tissues

Visualises physiological activity such as

• blood flow

• metabolism

Anatomical Imaging Nuc Med

Anatomical Imaging= uses various techniques to visualize the internal structures of the body

• Provides structural detail

• Key difference: function vs structure

Components of Gamma Camera

Components

• Collimator

• Scintillation Crystal

• Detector Heads

• CT

Radiation Safety Principles

• TDS: Time, Distance, Shielding

• ALARA: As Low as Reasonably Achievable

• Limitations: cannot use lead gowns when the pt is in the source

• Inverse square law: doubling distance reduces exposure by a factor of 4

Units of Measurement and Timing

• Becquerel (Bq): Decays per second

• Half life considerations: impacts image timing, shorter in PET vs traditional Nuc Med

• R(t) is the decay rate at time t

• R0 is the initial decay rate at time 0

• e is the base of the Naperian logarithms

• λ is the decay constant of the radioactive isotope

Quantification in Imaging

• Allows assessment of tracer uptake

• Both Dose and time are very important

• Important in MAG3, thyroid scans and more

Functional Imaging Pros and Cons

Functional Imaging Pros

• Detects early functional changes

• High sensitivity (true positive ratio)

Cons

• Poor anatomical detail

• Low specificity (true negative ratio)

Bone Scans

Advantages of Bone scans over Conventional Imaging:

• Early detection of bone metabolism changes, whole body screening

3 Phase Bone Scan: blood flow, blood pool, delayed.

Used for: osteomyelitis, prosthesis infection

SPECT/CT Benefits

SPECT: a nuclear medicine imaging technique that creates detailed, 3D images of organs, tissues, and bones by detecting the gamma rays emitted by radioactive tracers injected into the body

Benefits:

• Combines function and structure so improved localisation

Superscan

Intense skeletal uptake with reduced renal/ST activity (eg: metastatic disease)

Common Indications:

• ? bony mets

• Infection

• Trauma

• Arthritis

Thyroid Imaging Nuc Med

Dose Quantification: determines % uptake, guides diagnosis and therapy

Anatomical Localisation: using landmarks (eg sternal notch)

Iodine and CT contrast: contrast saturates thyroid. Wait 4-6 weeks post CT

Thyroid Imaging - Goitre

Goitre:

• Multinodular= heterogeneous

Thyroid Imaging - Graves

Graves= diffuse increased uptake

Lung Ventilation Perfusion (V/Q) Scan indications Nuc Med

Indication: Pulmonary Embolism

Lung Ventilation Perfusion scan Nuc Med vs CTPA

Lung (V/Q) Advantages:

• Contrast allergy

• Less ionising for pregnant patients

• Can image those with renal impairments

Pharmaceuticals used in Lung (V/Q) scans

Ventilation= 99mTc Technegas

Perfusion= 99mTc MAA

PE Appearance in Lung (V/Q) scan

Normal ventilation, perfusion defect (mismatch)

Poor image quality causes for Lung V/Q scan

COPD= poor ventilation distribution

Renal Imaging MAG3

A MAG3 renal scan uses radiopharmaceuticals and a gamma camera to highlight and take pictures of your urinary system

MAG 3 Indications

Indications:

• PUJ/VUJ obstruction

• Transplant work up

Renal Imaging DMSA

A DMSA renal scan is a diagnostic imaging exam that evaluates the function, size, shape, and position of the kidneys and detects scarring caused by frequent infections

PET/CT Nuc Med

PET Advantages:

• Better resolution

• Sensitivity than gamma camera

• Patient Prep: fast, no exercise, keep warm to reduce brown fat uptake

• Fluorodeoxyglucose Tracer: mimics glucose uptake, used in cancer and inflammation