How I Do It- Neck CT

Introduction to Neck CT Imaging

Good morning.

Not all neck CTs are the same.

Used to be, we'd put the patient on the scanner,
we'd ask the technologist to push a button,
the next CT would be done, and we'd be reading it and dictating a report.

And we can't do that anymore,
especially not in the United States where you're nobody
unless you've had a head CT or a neck CT.

Everyone in this room I bet,
has had a CT at one point or another.

We are radiation dose conscious now,
and we have to be very careful about how we do our scanning.

Objectives and Importance of Dose Reduction

At the end of this lecture,
I would hope that the attendee would understand
that dose reduction techniques are now available for CT.

They are very vendor specific
and the radiologist for the first time, well,
not the first time, but has to be cognizant of some
of the dose reduction techniques.

The importance of IV contrast in the neck cannot be
understated, and I've dealt my whole career with
what is the optimal neck IV contrast technique.

And the single best dose reduction technique is
to do the scan for the right reason on the right person.

Challenges in Neck CT Imaging

What I plan to do is go through some
of the CT neck challenges that we have,
and the neck is one of the most difficult places to scan and to interpret.

Most of our reports today have something tagged on the
beginning and the end, CTDI and DLP.

And I wanna review what those two phrases mean
and how the clinicians should be looking at them.

We'll be looking at some
of the scanner specific dose reduction techniques,
contrast technique, and look at the most efficient ways
to decrease radiation dose.

In my personal opinion, there's almost never an indication
to do without and with, we do it in the brain,
but we don't do it in the neck.

Avoid having to repeat a scan
and if it's not gonna answer the question,
don't do the scan.

And this is what I, one
of my pet peeves is patients scanned when they're clearly
not gonna get their clinical answer from a CT.

Lots of different challenges in head and neck CT imaging,
but the main one is
that their x-ray attenuation varies very little over the
soft tissues in the neck.

A neck node
and a neck muscle are very, very similar in density.

And that means we need something called the highest LCD,
which is a low contrast detectability.

Now, if there are a variety of artifacts that we deal with,
that these are more common in the brain, the aliasing
and the spectral artifacts,
but in the neck it's this concept of low contrast detectability.

Structures next to each other are nearly
iso dense on CT.

The two artifacts that we deal with the most as head
and neck imagers are the LCD and the suppression of motion artifact.

Patients are often moving in the scanner
or may move in the scanner.

They, especially if they have big head
and neck lesions, they are air hunger
and they're occasionally gasping for breath.

That's the patient who should not have a CT.

And so motion artifact is a really difficult problem.

It's not such a big problem when we do temporal bone imaging
or sinus imaging.

And with this type of imaging, CTs the gold standard
and we're really looking at only one density
and that's bone.

It's very easy to do our real thin reformations
to see this kind of anatomy at the frontal recess
with almost no dose to the patient.

The patient probably gets more radiation
by walking in the sunshine than from getting a sinus CT,
but it's not the same with neck scanning.

In fact, most neck scans potentially have
as high a radiation exposure as an abdominal CT,
and you can't pick up a magazine
or a newspaper today without seeing
how the public's being inundated
with dire warnings about radiation.

Dose Reduction Strategies

Here are the, at the very least,
radiologists should be familiar with these ways
to diminish radiation dose.

We're gonna review automatic exposure control, how to
what happens when you lower the mA
and the kVp, the concept of a noise index, which most
of us know what our noise index is on our CT.

And the newest way to decrease radiation is
with iterative reconstruction.

Automatic Exposure Control

This is the concept of automatic exposure control.

As of about 2006
when we scanned a neck, we used a uniform or fixed mA,
and the same body part got the same mA.

Whether you were at a thick area like the skull,
whether you were at the very thin area with that radiation
sensitive organ, the thyroid gland
or at the lung apex, you used a fixed mA
that was incredibly inefficient
because really what we need is more dose here,
much less dose here, both
because the volume of tissue is smaller
and we've got the thyroid gland there.

And then we need more dose here at the lung apex.

And the vendors described
and developed this technique of tube current modulation
and with tube current modulation.

The mA, which is the measure of tube current, varies
AEC across the course of the image location.

And this is called automatic exposure control, AEC.

And virtually every vendor
now has it available in their CT scanner,
and this should be routinely used.

Iterative Reconstruction

The second way that the vendors have dealt
with radiation exposure is iterative reconstruction.

If you have a GE shop, it's called ASIR
Adaptive Statistical Iterative Reconstruction.

The Siemens vendors call it IRIS
and Philips calls it iDose.

And it's really the same concept.

It's a reconstruction algorithm that reduces image noise
and during the course of this reduction will reduce
radiation dose
and routinely the dose during your scan can be reduced by
as much as 40%.

Actually, you can dial up your ASIR numbers
and reduce radiation dose to 90 or a hundred percent,
but it will look like you've scanned a Barbie doll
and not a human being.

So for most clinical imaging, we put our ASIR levels
to reduce dosage by about 40%.

This is a CT upgrade,
whether you're bringing in ASIR IRIS or iDose.

It is a financial package
that it is a CT upgrade to pre-existing CT scanners.

And then the radiologists must choose their iterative
reconstructive doses.

We usually use something so
that we get a dose reduction of 20 to 60%.

There is, other than just the financial upgrade,
a disadvantage.

And that is that using this may increase the time
of image reconstruction.

So you may need to let your ER know, you may need
to let your OR know,
or your surgeons know that we can scan their patients,
but the image reconstruction will be
increased by several minutes.

So we let our ER know that some
of our results may be 10, 15 minutes later
because we're taking care of their patients,
we're reducing their radiation by turning on our ASIR on our scanner.

Here are some examples of IRIS and ASIR.

This is a Siemens shop.

This is one way to increase that LCD by reducing noise.

So as we reduce noise, we are increasing the LCD.

This is a patient scanned without IRIS.

These were loaned to me by the Siemens company.

This is with IRIS.

This is about a 40 to 50% reduction in dose.

And you can see that at the same time we have a much
less noisy image.

We have a lot of noise here in this image.

It's smoothed out here with the IRIS.

And the most important benefit is
reduction in dose.

Yes, you can argue perhaps we might miss a very early,
small cerebral infarction,
but no, there has been no data as of yet showing that IRIS
or ASIR have reduced our ability to look at new
or small infarctions.

Here's a patient, this is at the vertex.

This isn't the neck, but obviously the brain.

And we've put on a, this is without
ASIR, this is with ASIR.

It's a smoother image, much less noise.

And this is a 40 to 50% reduction in dose.

So this is a package that you have
to purchase for your scanner.

I suspect in the next five years, this will be mandated
by the government.

Most of you are seeing routinely in the dictations the CTDI or DLP I'm currently put that in in my dictations.

Understanding CTDI and DLP

It is important to know that this is not the dose
that your patient got,
but this is a measure of the radiation output of
that particular CT scanner for that particular procedure.

So it's not a dose to the patient, it's what that scanner
did during the course of that scan.

Patient dose is so much more complicated.

It can be measured as a skin dose, an organ dose,
or a dose in the center of the scan.

You might ask, why don't we just dictate
how much dose your patient got?

And that's nearly impossible to do on the fly
because it's not scanner dependent, it's patient dependent.

So instead what we're reporting is the CTDI and the DLP,
and that's what they got from that particular scan.

The CTDI is the computed tomography dose index
and it is in units of mGy.

This is measured using a standard dose phantom.

And here's the definition of CTDI.

It's the average dose imparted by a single
axial acquisition to a standard phantom,
which is a pencil chamber dosimeter,
and it's over a width of 14 CT slices.

Most of our CT scans are far more than 14 slices,
and that's why we follow the CTDI report with a DLP.

This measures two types of radiation, the primary radiation,
and then the scatter radiation, which is significant in CT.

Now, as I said, no single method can estimate the dose
to all patients because it is tremendously variable.

Depends on the patient size
and what body part you're scanning.

But this is an estimate only of the exposure dose.

Anytime you see CTDI on your reported on your dictations,
the next thing you're probably seeing is a DLP,
and that's the dose length product.

And that takes the CTDI times the length
of the body part that was scanned.

This is in units mGy cm,
and that is the total radiation dose estimated from
that particular technique.

So these are two ways in our industry now
that we're letting you
and the patient know an estimate of their dose from
that particular CT scan.

Optimizing CT Techniques for Dose Reduction

So our current CT technique for radiology departments is
to use the lowest recommended dose possible.

And this has been very widely published in the pediatric
radiology literature,
but it's a huge importance right now in any radiology department,

we try to never repeat a scan.

In other words, we spend a lot of time
with our technologists training them about being able
to tell what patient maybe shouldn't have a scan right now,
let's wait five minutes, let them empty their bladder,
do something so that they,
the technologist can recognize the patient who's not
going to hold still.

We spend time with our patient education,
especially in our outpatient settings.

The technologist sits down with the patient,
looks them in the eye, talks
to them about radiation exposure and dosage
and really emphasizes why they need to hold still.

And then not all CT scans are the same.

Very important, especially for the clinicians to understand
that not every neck CT is the same.

We do our neck CTs for different indications
and we'll change our techniques depending
upon the indications.

We choose a noise technique which can really,
really affect radiation dosage if we're doing a screening.

'Cause someone has quote fullness in the neck,
which in my particular experience is a terrible reason to get a neck CT scan,
but we see it all the time.

I'll crank the noise index up to over 14
to decrease the radiation dose.

'Cause my gut feeling is it's gonna be a normal study.

On the other hand, if I'm looking at a patient
and I'm worried about a recurrent adenopathy in a patient
with a head and neck cancer, if I'm looking
for a parathyroid adenoma,
I'm gonna bring my noise index down to 12
or 14, which means I'm not gonna tolerate much
noise in my image.

But as a result, the radiation dose will go up.

All of our scans get automatic exposure control
and we are upgrading every CT scanner in our system
to the iterative reconstruction,
either the ASIR or the IRIS.

IV Contrast Techniques in Neck CT

I've spent most of my academic career trying to deal
with IV contrast
and IV contrast in the neck is such an enormous problem where there are so many variables
that we have when we decide the contrast,

we have the iodine concentration.

All of these vendors have different iodine concentrations.

What volume should I use? What rate should I use?

Should I follow with the saline flush?

Should I use a uni or biphasic bolus?

Tremendous number of choices.

There are scan factors so that not every head CT,
every neck CT is the same.

What will the scan duration be?

Have they upgraded my scanner to a 64 slice scanner
and forgot to tell me
that the neck will be scanned in nine milliseconds
as opposed to 20 seconds?

I'll still be giving a contrast injection.

When this patient's left the department, what kind
of scan delay should I use?

What is the circulation time between that brachial vein to the jugular veins and into the necrotic node?

So should I have a program scan delay
and should I use a dual phase scan?

So with contrast, there are a lot
of things we take into consideration body weight.

A patient who weighs a hundred pounds
because they've been dealing with cancer really shouldn't get the same amount of contrast
as the 350 pounder.

That is part of our normal daily life in radiology.

Now what amount should we use the delivery
and the delayed scan?

Those are all issues that are different
for every single patient.

There is a lot of interest right now in looking at things like the K edge
of iodine and what happens to the contrast
as you drop the kVp or the voltage in your scan.

As you drop the kVp from 120 to 80, the radiation dose
to the patient goes down 65%.

That's huge.

What happens to your contrast in your patient
with a lower kVp?

The contrast goes up
because it gets closer to the K edge of iodine.

So you can drop the amount
of contrast you use at a lower kVp.

Now these are, this makes telling you
what our protocol is nearly impossible
because it changes from patient to patient.

Are you measuring lean body weight
or overall body surface area fat is very avascular,
so just the patient's weight is a terrible way
to determine the contrast dose.

What you should be doing is looking at lean body weight
as your weight increases, whether it's fat
or muscle, the blood volume goes up.

So by definition, the iodine concentration is going
to go down, which leads to decreased enhancement.

And then the horrible problem of cardiac output.

All of us have looked at a scan
where we know we gave the patient 150 ccs, we know we did,
and there's very, very poor enhancement on the neck CT
and that's because they have an ejection fraction of 15%
that nobody told us about.

In these patients, the bolus is gonna arrive slowly.

The parenchymal enhancement is gonna be very prolonged.

You might wanna delay your scan for five minutes
after you give the contrast
and the washout will also be very delayed.

So we like to protocol every different neck CT differently.

Keeping in mind things like ejection fraction,
cardiac output, body weight,
and how the patient scan looked the last time they
get scanned at our shop.

Avoiding Without and With Contrast Scans

Now, except for the talk that you just heard about 4D CT,
in my opinion, we should never, ever, ever, ever
order a neck CT without
and with, I don't see any reason ever clinically
to scan a patient twice.

And the argument I hear from the OR the ENT surgeons is, well, I'll miss stones
and no, you won't miss stones
because stones are very, very dense.

Now that we don't have film, we have workstations,
we can sit at the workstation, we can play with the window
and level and even very small stones like you might see in
the parotid with Sjogren's,
we can see on a contrast enhanced CT scan.

So if my requisition, if the surgeon
or the clinician has asked for a neck without
and with, I will not do that.

I always do with alone.

Keep in mind there are some things to remember.

One might be if you're looking at a patient
with thyroid carcinoma
and you're planning a nuclear medicine study like a I-123
or I-131 study, once you flood them
with iodine,
those nuclear medicine studies will be unreliable
for four to six weeks.

The answer to me is not to do a neck CT scan without,
but it's to compromise and either do an MR
or an ultrasound,
but a neck CT without really is not indicated.

Reasons for Using IV Contrast

Here's the reason we use contrast.

We don't use contrast to find the vessels.

Everyone in this room can find the common carotid artery.

In the jugular vein, we use contrast to be able
to see a tumor
and see its interface with normal structures.

Now this is a very large salivary gland tumor,
minor salivary gland tumor in the palate.

Everyone in here would probably see this tumor even
without IV contrast.

But nonetheless, we use contrast to see the interface say
with the deep belly of temporalis muscle right here
or the OID musculature
or to see its effect here on the medial OID.

Look at this case. This case was called a normal neck CT
and this is not normal
and this is where we failed to use the contrast.

We have a nice normal aryepiglottic fold here,
normal piriform sinus,
but look at this abnormal enhancing mass here on the aryepiglottic fold and in the depths of this piriform sinus,

there's no way this is GERD or gastroesophageal reflux.

There's no way this is mucositis. This is a tumor.

And of course we have a metastatic level three node right here.

This study was called normal.

Pitfalls with IV Contrast

Here are a couple other pitfalls with IV contrast.

Here's a patient that got a big bolus of contrast.

Got a lot of radiation dose from the CT scan.

This was called fullness in the tonsil.

Otherwise normal, well this is a very large oropharyngeal squamous cell carcinoma.

It's a T4A, it's going into the floor of mouth
and the hyoglossus muscle is involved right here.

Great vascular enhancement,
but they didn't wait enough for the delay
and they probably didn't use enough contrast
to see any enhancement in this tumor.

Does it cross the midline?

Is the left geniohyoid complex involved.

This study has answered none
of the questions this patient needs
to have answered in order
to decide whether they're a surgical candidate.

Here's the patient that I just showed you
with the piriform sinus tumor.

This is a T1 piriform sinus tumor.

This is less than 5%
of hypopharyngeal squamous cell carcinoma is detected when
it's a T1, but you can see it nicely here
because it is excellent contrast.

Bolus interpretation is another problem.

Here's another pitfall you might see.

This is a patient who was asked
to take out their dentures when they came
to the radiology department and this is denture paste
and you'll see that all the time if you're sending a patient
for an oral cavity cancer
or if the patient's coming for an oral cavity cancer,
they really should be asked not
to wear their dentures that day.

Nobody follows that rule.

Nobody wants to leave without their teeth.

But it would be nice if the patients put in their
teeth after their scan, so get used
to seeing this high density along the alveolar ridge.

This is denture paste.

Here are three different dose studies.

These were neck CTs done for neck masses
and all three of 'em are terrible technique.

Here's a patient scanned for a neck mass.

You can see there's layering of contrast
and blood in the jugular vein.

Yes, you can see that medial line,
internal carotid artery elevating the posterior wall.

But there is no enhancement here in the mucosa
or in the structures in the floor of the mouth.

It's nice to be able to see the
enhancement in the vessels here.

The neurovascular bundle in the floor of the mouth.

Here's a patient scan for a neck mass.

The radiologist got lucky
because yes, it is a carotid body tumor
so they can see the mass here at the bifurcation of the carotid external and internal vessels.

But notice again, no enhancement here in the mucosa.

Terrible technique. Here's another poor technique CT scan.

Yes, we can see the styloid process, the carotid artery,
the clot there in the jugular vein.

But notice there's no enhancement here in the mucosa.

Be very hard. In fact,
it'd probably be impossible to stage a mucosal malignancy
with this type of enhancement pattern.

Be aware that with CTA we're scanning at 12 to 15 seconds after we give the contrast.

But for neck scanning, we're waiting longer.

Here's another pitfall.

Here's a patient who was scanned for a neck mass.

This was called lymphoma
because it's kind of a bland looking mass.

They did not use enough contrast.

The delay was too short
and in fact this was a necrotic node.

This is a squamous cell carcinoma.

So you will not see the necrosis in nodal disease
or in head and neck cancer if you don't use enough contrast
and your delay is too short.

Evolution of Contrast Techniques

I've been through so many different types of,
or so many different CT techniques during the past 24 years
that I've done head and neck radiology.

This is what we used to do, a big bolus of contrast.

We used to do two ccs per second and we wait 90 seconds
before we started the scan.

We lowered the dose if the patient weighed
125 pounds or less.

This is our new technique. We have an injector.

We're starting up the vein,
cleaning out the vein, if you will, with 20 ccs of saline.

We then give our first 55 ccs and we're programmed at two
and a half ccs per second.

Then we pause for two minutes
and that is a long pause if you're sitting at the scanner
because as radiologists we're
so worried about the contrast bolus being gone.

So it's that two minutes feels like forever.

But then we start an injection again to pacify the vessels.

And then we do, we clean out the vein, if you will,
with 40 ccs of saline and then we start our scan.

So we've given a big bolus of contrast right here
so it can kind of diffuse into whatever
tumor we're looking at.

And then at the end we're getting another bolus
to look at the mucosal enhancement
and to look at the vessels.

We have our patients quietly breathing.

Now a lot of clinicians thought
that we were having patients hold their breath,
but we have them quietly breathing.

If they hold their breath, their vocal cords are abducted
and we don't get a good look at the larynx
so they breathe quietly.

Our scanners today are so fast that they patients can be scanned during the respiratory phase.

We do ask them not to swallow,
which automatically makes everyone swallow.

So we have them swallow a couple times.

We coach them and then we have them not swallow
and of course don't move.

Our techs are given very strong instructions.

We have them point the nose to the ceiling
and have the patient straight in the scanner.

As Dr. Smoker commented,
symmetry on the neck CTs is really helpful
and the techs really spend a lot
of time putting these patients at ease,
helping them relax.

Patients are nervous, helping them relax so
that they can get a good scan.

We scan from the top of the orbits through the aortic arch.

A lot of times we don't know if there's a vocal cord palsy
and we wanna see the entire course of that left vagus and recurrent laryngeal nerve.

We include the tip of the nose to the back of the head.

That sounds so logical that I see so many outside scans
where the tip of the nose wasn't included on the scan
or the back of the occiput.

And if you have a patient with a skin cancer,
those occipital nodes may not be included.

Our technologists are asked to angle parallel
to the hard palate.

If we're doing a diagnostic and not a screening scan.

This is our noise index
and we do always re-angle at the end of the study
through the oral amalgam artifact.

Now I bet you can, you're thinking why does she bother doing
that if we're scanning at 0.625 and we can just reformat.

And this re-angled really helps if you're looking at an oral
cavity cancer or an oral cavity infection, it gives,
gives you just a little bit more detail
and it gives you another chance
to see the tumor or the lesion.

All of our patients are scanned at either one
or 1.5 millimeters and they're reconstructed at 2.5.

Field of View and Image Reconstruction

Here's what I mean by a correct field of view.

This was chosen by the technologist.

They knew the patient had a boil abscess
or who knew they had a neck mass
and did not include the anterior aspect of the face on this scan.

This is not my cropping,
this was an incorrect field of view.

Here's a patient with necrotizing fasciitis
who had a neck syndrome
and again, we don't have the entire neck on this scan.

The technologist has chosen too small a field of view.

This is what we send to PACS.

We send the thin images that we obtained with the scan.

I do not want to look at all those images.

So the technologists reconstruct them at 2.5
or three millimeters.

Those are the ones I sit down and read.

The technologists routinely send the coronal
and sagittal reformations, which I really like,
although I often will do my own reformats on a workstation.

This is what we all review.

We look at the soft tissue windows, the bone windows,
the lung apex, and then the reformations.

But we've got those thins in our back pocket.

If we're not sure if that's a transglottic tumor
or we're not sure if that floor
of mouth process is invading the mylohyoid,
we can take those thin source images into the workstation, play with them ourselves
and answer those critical questions.

That's why we send the thin images to PACS.

And so our clinicians will come to us
and say, what are all these things?

I see every time I open up my one of my patients.

What I would recommend is that you immediately go
to whichever package of axials has the fewest number
of images 'cause those are probably the ones you're most
likely gonna wanna review.

Examples of Adequate Mucosal Enhancement

Here are some great examples of mucosal enhancement.

Look at how robust this sub mucosal enhancement is here in
this patient who's had radiation.

This patient also came in with their dentures.

We see that artificial look
around the alveolar crest here in this denture patient.

But this is what you should be seeing on your patients.

When I say an adequate mucosal enhancement,
sometimes these patients have been treated
with anti-VEGF factors.

This patient's been treated with Avastin.

Makes it a little harder
to see this recurrence here at the interface
of this myocutaneous flap and the floor of the mouth.

But we can still with a good bolus,
even patients who've had radiation vasculopathy
and are treated with anti-VEGF
or anti EGFR factors,
we can see some enhancement in their recurrences.

Good contrast boluses will let you see the necrosis.

You'll be able to appreciate this recurrent necrotic node in
a patient who's been radiated
and you'll easily see
that this is not squamous cell carcinoma,
but is leukemia lymphoma.

Unnecessary Indications for CT Scans

Here are three unnecessary indications for CT scan.

It makes me crazy. Contrast
and enhanced CT for a small palpable mass.

Please consider ultrasound. It's palpable.

We can put the ultrasound transducer on the mass.

We can tell you right away what it is.

Contrast enhanced CT for fullness in the neck.

I sometimes I don't even wanna look at it
'cause I know it's gonna be normal.

Fullness in the neck I think is a terrible indication
to radiate a patient.

Consider ultrasound and contrast enhanced CT for a thyroid nodule.

Just never, never do that.

The thyroid gland is gonna enhance the nodule enhances.

It's as not, it's as indeterminate.

A nodule in a chest x-ray ultrasound is the indication in
my opinion for all of these clinical settings.

Summary

In summary,
the dose reduction technology right now is advancing rapidly
and every radiologist needs to put on their physicist hat with their CT.

Whatever you can do, avoid having to re-scan
and you do that by patient and technologist indication education.

Never order without and with.

I just never see an indication for that.

Make sure you standardize your angulation
and your scan coverage, knowing full well, you might have
to tailor that in some clinical settings
and find a dose technique that works
for your patient population.

If you're down in South Beach,
you probably have some slim 120 pounders up here in
Georgia, we've got scanners that'll hold 600 pounds.

Thank you for your attention.