ordering mri exams in nova...

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Ordering MRI Exams in Nova Scotia

Introduction

Referral and Triage Process

To refer a patient for an MRI study, a standard MRI requisition must be completed and faxed to the

hospital of your choice. All requests for MRI services are screened by a local radiologist for

appropriateness and triaged according to level of urgency. Please refer to the Canadian Association of

Radiologists Diagnostic Imaging Referral Guidelines (2012) for appropriate indications

(http://www.car.ca/en/standards-guidelines/guidelines.aspx ). Any requisition that lacks a detailed

written indication will be returned to the requesting physician. On reviewing the requisition, the

radiologist may: return the request as not indicated, return the request for more information, suggest or

book an alternate investigation.

Wait Times

MRI wait times vary across the province and can be lengthy for non-urgent or routine cases at some

hospitals. Referring physicians are encouraged to consult the Nova Scotia Wait Time Website at

http://waittimes.novascotia.ca/ to help guide decisions about referral location for patients who are able

to travel. Physicians are asked to send requisitions to only one hospital, as simultaneous requests to

multiple hospitals block openings and contribute to longer wait times.

Family Physician and Nurse Practitioner Ordering

Starting in February 2013, all family physicians and Nurse Practitioners in Nova Scotia may order adult

MRI services directly without prior approval from a specialist or radiologist. The ability to order MRI

services directly is based on a phased approach by body region beginning with investigations for central

nervous system (brain), head and neck conditions starting February 28, 2013. The subsequent phases

are tentatively scheduled as follows:

Spine – June 2013

Musculoskeletal System – September 2013

All Other – December 2013

Pediatric MRI exams and breast MRI exams are excluded from the new policy and will continue to follow

existing ordering protocols.

MRI Safety

Some patients cannot safely undergo MRI because they have metallic foreign bodies in the eye or

certain implanted medical devices in their bodies. Patients with severe renal failure cannot safely

undergo gadolinium enhanced MRI. It is very important to fill out the safety information on the MRI

requisition. Many implanted medical devices are MRI safe. Information about specific devices can be

obtained at www. mrisafety.com.

http://www.car.ca/en/standards-guidelines/guidelines.aspx

http://waittimes.novascotia.ca/

http://mrisafety.com/

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Approximately 10% of patients experience significant claustrophobia in the MRI scanner. If

claustrophobia is likely, it is the referring physician’s responsibility to prescribe an oral sedative (most

commonly sublingual lorazepam) and instruct the patient to take the medication prior to the scan.

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Summary of Ordering Guidelines

The following summary is based on the Canadian Association of Radiologists Diagnostic Imaging Referral

Guidelines (http://www.car.ca/en/standards-guidelines/guidelines.aspx). A copy of the full guidelines by

condition or body region follows this summary. Physicians are encouraged to consult the full guidelines

for more detailed information on recommended imaging for the wide range of patient conditions.

Central Nervous System (Brain), Head and Neck Conditions

CT is ALWAYS preferred over MRI for the following indications:

Assessment of trauma to jaw, face and skull bones

Assessment of paranasal sinus inflammation

Initial assessment of scalp and skull lesions

Rule out intracranial hemorrhage

CT is more efficient and provides satisfactory diagnostic information for the following urgent

indications:

Rule out space occupying lesion

Rule out hydrocephalus

Rule out ischemic stroke

Rule out intracranial hemorrhage (intracerebral, subarachnoid, subdural, epidural)

MRI is preferred over CT for the following indications, but please note that wait time will vary on a

case-by-case basis with the strength of the indication (relevant details from the history, physical

examination and laboratory studies will greatly assist the triaging radiologist):

New focal neurological deficit referable to brainstem/cranial nerve(s)

Rule out encephalitis

Rule out or follow-up demyelinating disease

Rule out or follow-up sellar lesion (e.g. pituitary adenoma)

Rule out or follow-up cerebellopontine angle lesion (e.g. vestibular schwannoma)

Depending on the condition in question, it may still be most appropriate to refer a patient for a

consultant’s opinion prior to requesting an imaging procedure. Please consider the following common

neuroimaging requests from this perspective:

Headache – Imaging seldom alters the management of patients with chronic or recurrent headache,

lacking “red flags” (e.g. rapidly changing pattern, waking from sleep, new neurological deficit, history of

cancer or immunodeficiency). Nevertheless, imaging may be important to provide reassurance to

patient and doctor regarding potential serious pathology. In this scenario, CT can rule out a mass,

hydrocephalus and hemorrhage quickly and accurately.

http://www.car.ca/en/standards-guidelines/guidelines.aspx

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Intracranial aneurysm – The risk of harbouring an asymptomatic intracranial aneurysm increases steeply

for patients who have TWO or more affected FIRST DEGREE relatives. Patients with autosomal dominant

polycystic kidney disease are also at markedly increased risk. The choice to screen or not to screen must

take into consideration the dilemma that may arise if a tiny aneurysm is found. MRA and CTA are

essentially equivalent for screening purposes. MRA is preferable, as it avoids radiation and contrast

enhancement. Wait times are long, commensurate with the very low annual risk of rupture of most

asymptomatic aneurysms.

Dizziness – The yield of imaging, with CT or MR, in patients with uncomplicated dizziness (i.e. no specific

brainstem or cranial nerve findings) is low. Patients with true vertigo are best served by ENT evaluation.

Only a subset of these patients will benefit from further assessment with MRI to rule out retrocochlear

pathology.

Dementia – Imaging most commonly yields non-specific findings. From a practical point of view, CT can

rule out a space occupying lesion. CT can provide evidence in support of the clinical diagnoses of

vascular dementia and normal pressure hydrocephalus. MRI is more sensitive than CT for small vessel

ischemic changes, if vascular dementia remains a clinical concern after a non-contributory CT

examination. Neurological and/or neuropsychological assessment may be the next best step if less

common etiologies of dementia that have specific MRI findings are being considered.

Orbital pathology – MRI is best suited to study the soft tissues of the orbit. However, MRI examination

is best used in a targeted fashion, either to confirm an abnormality suspected on fundoscopy or to

identify an abnormality that is not accessible to fundoscopic examination. In some cases, MRI must

address inflammatory or neoplastic differential diagnostic considerations, while in other cases, vascular

imaging may be more appropriate. Therefore, ophthalmological referral is the best first step to

determine the need for MRI and also to guide the MRI examination, potentially maximizing its yield.

Head and neck masses – CT is routinely used to confirm and characterize cystic and solid masses in the

head and neck, and to stage cancers of the head and neck. MRI can accomplish the same without

ionizing radiation. However, MRI is more susceptible to motion artefact (swallowing, breathing, vascular

pulsation). Both modalities are susceptible to artefact from dental amalgam and appliances. MRI is

typically used as a problem-solving tool in patients with a documented abnormality that is incompletely

characterized on CT or ultrasound.

Temporomandibular joint pathology – MRI is superior to plain radiography and CT, because it can

demonstrate meniscal pathology as well as bony pathology. However, the precise definition of meniscal

pathology is most important for the planning of interventions in patients with established TMJ disease.

MRI should be reserved for this purpose.

Section A: Central nervous system

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Clinical/Diagnostic Problem

Investigation Recommendation(Grade)

Dose Comment

A01. Congenital disorders of the brain

(For children see L01)

MRI Indicated [B] 0 MRI is the best imaging modality for all malformations of the brain.

A02. Acute stroke CT Indicated [A] dd Modern treatment protocols require CT or MRI at the earliest possible time in all cases of suspected stroke in order to allow initiation of treatment as soon as possible. CT is generally preferred based on availability and because it can be obtained quickly, without MR safety screening. Most Canadian centres use CT as the primary modality for investigating acute stroke.

MRI Indicated [A] 0 Modern treatment protocols require CT or MRI at the earliest possible time in all cases of suspected stroke in order to allow initiation of treatment as soon as possible. MRI is a problem solving tool. It is particularly helpful in the evaluation of posterior fossa stroke.

CTA Specialized investigation [A]

dd Urgent vascular imaging with CTA can help to guide patient management.

MRA Specialized investigation [B]

0 Urgent vascular imaging with MRA can help to guide patient management.

SPECT or PET Not Indicated dd Not indicated in the acute setting.

A03. Transient ischemic attack (TIA)

(See also B09)

CTA Indicated [A] dd Urgent vascular imaging should be performed in all cases of high-risk TIA.

MRA Indicated [B] 0 Urgent vascular imaging should be performed in all cases of high-risk TIA.

US carotids Indicated [B] 0 Ultrasound can be an effective tool for screening the cervical common carotid and proximal internal carotid arteries but does not offer information on intracranial circulation. It is operator-dependant. If intervention is planned, a confirmatory CTA, MRA or DSA is recommended.

SPECT or PET Not indicated dd Not indicated in the acute setting.

A04. Multiple sclerosis and other white matter disease

MRI Indicated [A] 0 MRI is the best imaging modality for diagnosis and follow-up of multiple sclerosis and for investigating other forms of white matter disease.


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Dose Comment

A05. Headache: acute, severe, “thunderclap”; suspect subarachnoid hemorrhage (SAH)


CT Indicated [B] dd CT should be obtained urgently.

CTA Specialized investigation [C]

dd CTA should be used to identify an aneurysm or other vascular malformation if there is a subarachnoid hemorrhage.

DSA Specialized investigation

dd DSA should be limited to solving problems where diagnostic problems persist after CTA.

A06. Headache: chronic / recurrent

(See also B01)

(For children see L09 )

CT Indicated in specific circumstances [B]

dd CT is an excellent modality to screen for significant intracra-nial pathology. In the absence of focal features imaging is not often helpful. The following features significantly increase the likelihood of finding a major abnormality and justify request-ing diagnostic imaging:

• Recent onset and rapidly increasing frequency and severity of headache

• Headache causing the patient to wake from sleep• Associated dizziness, lack of coordination, tingling or

numbness, new neurologic deficit • New onset of a headache in a patient with a history of

cancer or immunodeficiency

If imaging is indicated, CT can be used; however radiation is a consideration particularly for repeat examinations.

MRI Indicated only in specific circumstances [C]

0 In the absence of focal features imaging is not often helpful. The following features significantly increase the likelihood of finding a major abnormality and justify requesting diagnostic imaging:

• Recent onset and rapidly increasing frequency and severity of headache

• Headache causing the patient to wake from sleep• Associated dizziness, lack of coordination, tingling or

numbness, new neurologic deficit • New onset of a headache in a patient with a history of

cancer or immunodeficiency

MRI provides more detailed images of the brain than CT.

A07. Headache: low pressure

MRI Specialized investigation [C]

0 In the presence of intermittent headache happening when upright and disappearing while recumbent, MRI is the best investigation. If there is a clinical indication for determining the site for a CSF leak, cisternography can be performed using MRI, CT or NM.

CT Specialized investigation [C]

dd When MR is not available or contra-indicated, CT can be used.


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Dose Comment

A08. Pituitary and juxtasellar problems

MRI Specialized investigation [B]

0 If vision is deteriorating the examination should be done as soon as possible. CT can be used if MRI is unavailable or contraindicated.

SXR Not indicated [C] d Patients who require investigation need MRI

A09. Posterior fossa signs

MRI Indicated [A] 0 MRI is the imaging modality of choice.

CT Indicated [A] dd CT is an acceptable alternative if MRI is unavailable or contraindicated.

A10. Hydrocephalus, suspect shunt malfunction

(For children see L04 – L05)

CT Indicated [B] dd CT is approrpriate for most cases.

MRI Indicated [B] 0 MRI is effective and has no radiation dose.

XR of entire shunt tube

Indicated in specific circumstances [C]

d If there is evidence of shunt malfunction on imaging, XR may be used to diagnose a break in the shunt tubing.

NM Indicated [C] d A radionuclide shunt study can evaluate shunt function.

A11. Middle or inner ear symptoms (including vertigo)

CT Specialized investigation [B]

dd Referral to a specialist should precede imaging, as these symptoms requires ENT, neurological, or neurosurgical expertise.


0 Referral to a specialist should precede imaging, as these symptoms requires ENT, neurological, or neurosurgical expertise.

A12. Sensorineural hearing loss


0 Referral to a specialist should precede imaging.

A13. Dementia and memory disorders, first-onset psychosis

CT Indicated dd CT is indicated to screen for common causes of these disorders.


0 This is the most sensitive and specific imaging modality to exclude treatable causes.

PET Specialized investigation [B]

dd Brain FDG-PET is the most sensitive and specific imaging modality to detect and categorize dementia and memory disorders.

It is especially recommended in cases of clinical doubt between Alzheimer’s disease and fronto-temporal dementia.

It can identify among patients presenting with mild cognitive impairment (MCI) which ones are at risk of conversion to Alzheimer’s disease.


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Dose Comment

A14. Acute visual loss: visual disturbances

XR Not indicated [A] d

MRI Specialized investigation [A]

0 Specialist can diagnose many cases without imaging. However, if imaging is indicated, MRI is the best imaging modality.

CT Specialized investigation [A]

dd CT may be used if MRI is unavailable or contraindicated.

A15. Epilepsy (adult)



0 Imaging is not required in patients with idiopathic generalized epilepsy. If imaging is clinically indicated, MRI is the modality of choice.

Impending guidelines: A16 Movement disorder

Section B: Head and neck

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Dose Comment

B01. Sinus disease

(For children see L11 – L14)

CT sinus Indicated only in specific circumstances [B]

d Acute sinusitis can be diagnosed clinically. If the symptoms persist for more than 10 days on appropriate treatment, low dose CT of the sinuses may be required. CT is also indicated if there are orbital signs or symptoms or if the patient is immunocompromised.

XR sinus Indicated only in specific circumstances [B]

dd Low dose CT is the examination of choice in acute sinusitis, but XR is a reasonable option if CT is unavailable.

B02. Orbital lesions MRI Specialized investigation [A]

dd MRI is the modality of choice for investigating problems such as proptosis.


dd CT may be used if MRI is unavailable and may complement MRI in the characterization of lesions, e.g. calcification.

US Specialized investigation [C]

0 US can be used for intraocular lesions.

XR Not indicated [A] d X-ray is not a sufficiently sensitive modality to justify its use for this condition.

B03. Orbital lesions: trauma

CT Indicated [A] dd CT is indicated when an orbital fracture is suspected.

B04. Orbital lesions:suspected foreign body

XR orbits Indicated [A] d XR is the only imaging required to exclude a metallic foreign body.


dd Indicated when XR does not show a foreign body but one, which may not be metallic, is strongly suspected, when multiple foreign bodies are present, or when it is not certain whether a foreign body is intraocular.

US Indicated [C] 0 US can also be used for radiolucent foreign bodies or where XR is difficult.

B05. Thyroid nodules US Indicated only in specific circumstances [B]

0 In patients with a palpable thyroid nodule and a normal or high serum TSH US should be performed to confirm the presence of a nodule and to determine if there are multiple nodules.

NM Indicated only in specific circumstances [C]

d Thyroid scanning is indicated in patients with a palpable nodule and a low serum TSH. Cold nodules should be assessed with US.

US-guided Fine-needle aspiration biopsy

Indicated [B] 0/0 Indicated in all nodules >1-1.5 cm. following US assessment, unless they have a typically benign appearance.


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Dose Comment

B06. Thyrotoxicosis NM Indicated [B] d A thyroid uptake and scan is often required to determine the underlying cause of hyperthyroidism and to guide treatment decisions.

B07. Ectopic thyroid tissue (e.g. lingual thyroid)

NM Indicated [C] d A thyroid scan is effective for locating ectopic thyroid tissue.

B08. Hyperpara-thyroidism

US Specialized investigation [C]

0 The imaging modality used is dependent on local experience and expertise.

NM Specialized investigation [C]

dd A parathyroid scan can help distinguish between parathyroid adenoma and hyperplasia in patients with a high clinical suspicion of hyperfunctioning parathyroid tissue.

CT Specialized investigation [C]

dd CT may be useful where the parathyroid scan is negative and to improve localization of parathyroid adenoma.


0 MR may be useful where the parathyroid scan is negative and to improve localization of parathyroid adenoma.

B09. Asymptomatic carotid bruit

US carotids Indicated only in specific circumstances [B]

0 Although US can detect carotid stenosis, it is not usually indicated because surgery is not recommended for asymptomatic carotid stenosis.

B10. Swallowed or inhaled foreign body

(See also J27 – J29)

(For children see L46, L47, L58)

Lateral XR soft tissues of neck

Indicated only in specific circumstances [B]

d Only indicated if a radio-opaque foreign body is suspected. If the clinical history and findings suggest the presence of a foreign body, direct examination of the oropharynx, laryngoscopy, and endoscopy are the investigations of choice.

B11. Neck mass of unknown origin

US Indicated [C] 0 US is the best initial imaging modality for assessing a neck mass. It can be combined with FNAC.

CT Indicated only in specific circumstances [C]

dd CT could be used to determine the full extent of large lesions not fully visualized by US.

MRI Indicated only in specific circumstances [C]

0 MRI could be to determine the full extent of large lesions is not fully visualized by US.


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Dose Comment

B12. Salivary obstruction

US / Sialogram/MRI

Indicated [C] 0/d/0 Imaging is indicated to assess possible salivary obstruction in patients with intermittent, food-related swelling. The choice of imaging depends on local experience and expertise.

XR Indicated only in specific circumstances [C]

d XR can be used to rule out a salivary duct calculusin the floor of the mouth.

B13. Salivary mass US Indicated [B] 0 US is the best initial imaging modality for a suspected salivary mass; it can be combined with FNAC, if necessary.

MRI / CT Specialized investigation [B]

0/dd If extension into deep spaces of the neck is suspected, MRI or CT should be carried out.

B14. Dry mouth: connective tissue disease

NM Specialized investigation [C]

d Radionuclide sialoscintigraphy is a useful test to document the function of the major salivary glands

B15. Temporomandibular joint dysfunction


0 MRI is the best imaging modality to show internal derange-ment of the temperomandibular joint, but it should only be ordered by a specialist or after consultation with a radiologist.

XR Not Indicated d XR is not usually helpful because it shows only late bony changes not the internal derangement which causes the symptoms.

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