Wednesday 30 October 2019

MRI Artifact

The individual topics covered in this section are:

1. Tissue-related Artifacts
2. Motion-related Artifacts
3.Technique-related artifacts

Magnetic Resonance (MR) Defecography

Magnetic resonance (MR) defecography is a noninvasive test that uses magnetic resonance imaging to obtain images at various stages of defecation to evaluate how well the pelvic muscles are working and provide insight into rectal function. It is used to help determine the cause of fecal incontinence, constipation, and other conditions such as pelvic organ prolapse that may interfere with a person's ability to pass stool.

Blood clots are

1. semi-solid masses of blood that can be stationary (thrombosis).

2. block blood flow or break loose (embolism) .

Blood clots can be life-threatening depending on their location and severity.

What is CT or CAT Scan?

Computerized Axial Tomography Scan:

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What is Arcoxia ?

What is Arcoxia?

Arcoxia is used for the following:

acute and chronic treatment of the signs and symptoms of osteoarthritis and rheumatoid arthritis
management of ankylosing spondylitis
relief of chronic musculoskeletal pain
relief of acute pain
to treat acute gouty arthritis

Diffusion Weighted Imaging

DWI is a form of MR Imaging based upon measuring the random Brownian motion of water molecule within voxel of tissue.

In generally simplified term Highly Cellular tissue or Those with Cellular Swelling exhibit Lower Diffusion Coefficient.

Diffusion is particularly useful in Tumour Characterisation and Cerebral Ischemic .

A great deal of confusion exists in the way the clinician and radiologist refer to diffusion restriction , with both groups often appearing to not actually understand what they are referring to.

The term of Diffusion Weighted Imaging is used to denote a number of different thing .

1. Isotropic Diffusion Map ( What the radiologist and Clinician will refer to as DWI ).

2. The various Pulse sequence that result in the generation of various images ( Isotropic map , B:0 , adc).

3. The more general term to encompass all diffusion technique including diffusion tensor imaging .
To make matters worse, many are not aware of the concept of T2 shine-through, a cause of artefactual high signal on isotropic maps, or interpret it as a binary feature with T2 contribution to signal either present or absent when in reality there is always a T2 component even to regions with true T2 diffusion restriction.
A much safer and more accurate way of referring to diffusion restriction is to remember that we are referring to actual apparent diffusion coefficient (ADC) values, and to use wording such as "the region demonstrates abnormally low ADC values (abnormal diffusion restriction)" or even "high signal on isotropic images (DWI) is confirmed by ADC maps to represent abnormal restricted diffusion".

MRI Prostate ?

MRI of the prostate is primarily used to evaluate prostate cancer. Your doctor will use this exam to:

What is Pulmonary Embolism?

A pulmonary embolism occurs when a blood clot moves through the bloodstream and becomes lodged in a blood vessel in the lungs. This can make it hard for blood to pass through the lungs to get oxygen. Diagnosing a pulmonary embolism can be difficult because half of patients with a clot in the lungs have no symptoms. Others may experience shortness of breath, chest pain, dizziness, and possibly swelling in the legs. If you have a pulmonary embolism, you need medical treatment right away to prevent a blood clot from blocking blood flow to the lungs and heart.

Your doctor can confirm the presence of a pulmonary embolism with CT angiography, or a ventilation perfusion (V/Q) lung scan. Treatment typically includes medications to thin the blood or placement of a filter to prevent the movement of additional blood clots to the lungs. Rarely, drugs are used to dissolve the clot or a catheter-based procedure is done to remove or treat the clot directly.

What os Computed Tomography (CT) - Body?

Computed tomography (CT) of the body uses sophisticated x-ray technology to help detect a variety of diseases and conditions. CT scanning is fast, painless, noninvasive and accurate. In emergency cases, it can reveal internal injuries and bleeding quickly enough to help save lives.

Introduction MRI

Magnetic Resonance Imaging (MRI) is a spectroscopic imaging techniques used in medical setting to produce imaging of the inside body.

Tuesday 9 July 2019

What patients are considered high risk patients for IV contrast for CIN?

This answer is very broad but here are some typical responses :

The patient with a history of renal disease especially if the patient is a diabetic
A patient on certain known nephrotoxic drugs such as aminoglycosides and amphotericin B
Dehydrated patients regardless of the cause
Patients with poor cardiac status including congestive heart failure
Patients with multiple myeloma
Patients with recent contrast injection of more than 100-120 ml in the preceding 24 hours (potential increased risk)

Do we have set cutoffs for creatinine levels and if so what are they?

Although this will vary on the patient and the importance of the study general guidelines are that for creatinines under 1.7 we will use Omnipaque-350. For creatinines of 1.8-2.1 or so when the study is needed we use Visipaque-320. Please note that we will make certain to minimize the contrast volumes in patients with the use of saline flush or just smaller volumes of contrast. On select studies we can use as little as 60 ml of contrast. Remember that there is no threshold of contrast volume for inducing CIN but it is uncommon with volumes of 100 ml or less.

Can we pretreat patients who have borderline renal function? If yes then how?

Two common regimens are the use of bicarbonate in solution as part of a prestudy ( and often post study protocol) hydration protocol

Use of N-Acetylcysteine (meta-analysis showed no advantage although recent article was more positive about its use)

Should patients be NPO for CT scanning? If yes for how long?

We like the patient to be NPO for food for a minimum of 3 hours. However, fluids are encouraged (water is best) to keep the patient well hydrated. Dehydration is a leading factor for development of CIN.

Monday 8 July 2019

What are the common volumes of contrast used for IV injection?

With the newest 64 MDCT scanners most patients have contrast volumes in the 100-120 ml range. We find that for many applications 100 ml of contrast works fine. Please note that in the past many sites used 150-200 ml of contrast for abdominal/liver CT and CT angiography.

What are the common volumes of contrast used for IV injection?

The best site for IV access is the right antecubital fossa. This site provides a combination of optimal safety plus a good point to time delivery of contrast in studies such as cardiac CTA and pulmonary embolism studies. The left antecubital fossa would be our second choice.

We prefer an 18g angiocatheter in the antecubital fossa when possible. This typically can easily accept injection rates of 5 cc/sec without any problem. We will use a 20g when an 18g is not possible. For 20g we can inject up to 4 cc/sec safely.

What kind of IV access is ideal for use for IV contrast injection?

Has there been any new developments in technology that may help us high injection rates in patients who can not tolerate an 18g needle (or at times even a 20g)?

The answer is yes. This past year the Nexiva Diffusics catheter got FDA approval for use. This allow us to use smaller needles and still get high injection rates. The 20g Diffusics can inject up to 10 cc/sec and the 22g up to 6.5 cc/sec. This is a major step forward.

IV Catheter Safety

Most IV catheters are pressure rated and usually the safety on the injector is for a pressure of 300 psi or less. Exceeding this can result in product leakage and or damage to the catheter and potentially injury to the patient
Some of the newer generation IV catheters like the BD Nexiva Diffusics can be used to a psi of 325
Please be certain that you are aware of what catheter you use and in practice it is ideal to use one brand only to prevent errors in setting the psi values in routine practice

"The purpose of this study was to compare the performance of a 20-gauge fenestrated catheter with an 18-gauge nonfenestrated catheter for i.v. contrast infusion during MDCT."

I.v. contrast administration with dual source 128-MDCT: a randomized controlled study comparing 18-gauge nonfenestrated and 20-gauge fenestrated catheters for catheter placement success, infusion rate, image quality, and complications.
Johnson PT, Christensen GM, Fishman EK.
AJR Am J Roentgenol. 2014 Jun;202(6):1166-70.

"A 20-gauge fenestrated catheter performs similarly to an 18-gauge nonfenestrated catheter with respect to i.v. contrast infusion rates and aortic enhancement levels and can be placed in most subjects whose veins are deemed insufficient for an 18-gauge catheter."

Hardware: IV Access Device

BD Nexiva Diffusics
Injection Rates

BD Nexiva Diffusics

"Experienced IV starters usually achieve IV access in one attempt by tailoring IV catheter gauge to vein quality; however, target infusion rates are not likely to be achieved with 22- and 24-gauge catheters, used in nearly 1/3 of the patients in this study."

Catheter insertion for intravenous (IV) contrast infusion in multidetector-row computed tomography (MDCT): defining how catheter caliber selection affects procedure of catheter insertion, IV contrast infusion rate, complication rate, and MDCT image quality.
Johnson PT, Christensen G, Lai H, Eng J, Fishman EK.
J Comput Assist Tomogr. 2014 Mar-Apr;38(2):281-4

20 G Nexiva Diffusics
10.0 cc/sec injection rate

22 G Nexiva Diffusics
6.5 cc/sec injection rate

24 G Nexiva Diffusics
3.0 cc/sec injection rate

Nexiva in Use

Standard 18g vs Nexiva 20g

Nexiva Kit

20. Can any IV the patient has in place be used to inject the contrast material?

A 18-20 g IV line can be used with the caveat that the line functions well on test injections and the line can be monitored during the injection of the contrast.

A line covered by excess tape or gauze should not be used unless the gauze or tape can be removed to access/monitor the patients injection site. Not following this rule religiously will result in errors

Can we use a central line or a PICC line for injection?

Hospital policies will vary but at Hopkins we have several well defined policies. They include:

Standard PICC lines can not be used for IV injections
Central lines can be injected by hand but not with power injectors. This policy is not a universal one
For information purposes some sites allow power injection into central lines with a limited flow rate (2 cc/sec) or at a lower preset pressure rating on the injector
Under no circumstances should PICCs be used with power injectors. They can shear or break.

What are some of the common normal “side effects” of IV contrast agents?

RadiologyInfo.org which is sponsored by RSNA and the ACR notes that “When an iodine-based contrast material is injected into your bloodstream, you may have a warm, flushed sensation and a metallic taste in your mouth that lasts for a few minutes.”

They then divides reactions into mild, moderate and severe. The mild reactions might be considered normal in many ways although any hives would raise concern for the next time IV contrast is used. Here is the info from RadiologyInfo .org

Is it ok for patients to have both an MR and a CT with contrast on the same day

This question was addressed on the RSNA site and there is no issue doing both MRI and CT the same day with Gadolinium and Iodinated Contrast.

Here is more detailed information courtesy of Richard A. Vitti MD from Medical Affairs at GE Healthcare.

CT contrast, or X-ray contrast for IV use, is usually an iodinated compound, whereas most MRI contrast media contains a heavy metal ion usually gadolinium. Iodine provides contrast by virtue of absorption of X-rays at the K-edge. Gd provides contrast in MR by changing the magnetic moment. Generally these agents distribute themselves from the vascular space to the interstitial space of soft tissues, and are elminated by glomerular filtration by the kidneys.

Are there any contrast volume limitations for the use of IV contrast?

Traditionally contrast dose for adult body CT is given in ranges of 50ml – 200ml, depending on procedure (hepatic, renal…) and iodine concentration (270mgI/ml to 400 mgI/ml). With increasing awareness of CIN and radiation dose, the trend has started to shift toward contrast dose by body weight. Some device manufacturers like Medrad (P3T) have introduced power injectors that follow a dose by weight protocol. There are a few studies published on weight-based dose for adults. Below are several examples.

What the meaning of GFR ?

Glomerular Filtration Rate (GFR) and Creatinine Clearance (CrCl) in Health and Disease: Using Popular Formulae (September 2009)

CSF flow studies

CSF flow studies are performed using a variety of MRI techniques and are able to qualitatively assess and quantify pulsatile CSF flow. The most common technique used is time-resolved 2D phase contrast MRI with velocity encoding.

MRI pulse sequence abbreviations

This article contains a list of commonly and less commonly used MRI pulse sequence abbreviations and their meaning. If available, an explanation is included in a separate article.

MRI sequence

An MRI sequence is a number of radiofrequency pulses and gradients that result in a set of images with a particular appearance. This article presents a simplified approach to recognizing common MRI sequences, but does not concern itself with the particulars of each sequence.

For a more complete and accurate discussion please refer to MRI pulse sequences.

MRI safety

MRI scanners, although free from potentially cancer-inducing ionising radiation found in plain radiography and CT, have a host of safety issues which must be taken very seriously. MRI safety can be divided into:

main magnetic field
varying magnetic (gradient) fields
radiofrequency

Spiral pulse sequences

Spiral scanning in MRI is unlike spiral scanning in CT where the x-ray tube is continuously rotating and data is continuously being acquired. In MRI the word "spiral" refers to the pattern of sampling k-space. In conventional imaging sequences including spin echo and gradient echo and in fast imaging sequences, a line or multiple lines of k-space in the frequency direction are acquired consecutively. In spiral scanning, k-space is acquired in a spiral trajectory. The entire k-space can be acquired during a single acquisition, or interleaved using more than one acquisition. This sequence allows faster image acquisition than the fast echo sequences but is slower than echo-planar imaging. Spiral scanning tends to have fewer artifacts than echo-planar imaging since adjacent points in k-space are acquired in close temporal proximity. The figures to the right show how the acquisition of data in k-space is done with conventional sequences and with spiral scanning.

PD weighted spin-echo images

Proton-density weight images are related to the number of nuclei in the area being imaged (number of hydrogen protons), as opposed to the magnetic characteristics of the hydrogen nuclei. They are produced from the first echo. PD weight images result when the contribution of both T1 and T2 contrast is minimized. They have a long TR (2000+ms) to minimize T1 differences because all tissues exhibit full longitudinal relaxation prior to the next 90 degrees RF pulse. They have a short TE (TE1, 20ms) to minimize T2 differences. High PD tissues appear bright.

Fast spin echo

Fast or turbo spin echo (FSE/TSE) is an adaptation of conventional spin-echo (SE) acquisition technique designed to reduce imaging time. It has largely supplanted the original spin-echo technique due to vastly improved imaging speed.

T2 weighted

T2 weighted image (T2WI) is one of the basic pulse sequences in MRI. The sequence weighting highlights differences in the T2 relaxation time of tissues.

MRI sequences

What is your consent policy in an emergency?

What if the patient is unable to sign consent what do we do?

Who gets the signed consent?

Do you need consent for oral or rectal contrast?

Do you need consent for IV contrast?

he patient has sickle cell disease. Can they get IV contrast?

The patient has multiple myeloma. Can they get IV contrast material?

If a patient has thyroid disease is iodinated contrast contraindicated?

If a patient has thyroid cancer is iodinated contrast contraindicated?

. Who should get baseline serum creatinine levels before CT?

Who should get baseline serum creatinine levels before CT?

If a CT is done on a pregnant patient and iodinated contrast is used can that affect the fetus?

What is our policy for scanning a pregnant patient?

If a patient is nursing can she receive IV contrast?

Can you use iodinated contrast on a patient with suspected or known pheochromocytoma?

Is there any problem with using iodinated contrast for CT if a patient is on the cardiac drug Amiodarone?

What are the current guidelines for patients taking metformin and needing a contrast study?

What are the current guidelines for Metformin and Iodinated Contrast agents?

If a patient has myathenia gravis should iodinated contrast be used for a chest CT?

If a patient is on glucophage (or other oral diabetes medications) is there an issue with iodinated contrast agents? What is the current rule with oral diabetes drugs? (glucophage)

If a patient is on glucophage (or other oral diabetes medications) is there an issue with iodinated contrast agents? What is the current rule with oral diabetes drugs? (glucophage).

What patients take glucophage (metformin)?

Metformin is approved by the FDA for first line treatment of Maturity Onset Diabetes Mellitus (NIDDM) and is used after diet alone fails.

What are the other names for metformin?

These brand names include; Glucophage, Glucophage XR, Glumetza, Fortamet, Riomet, Glucovance, Metaglip, Avandamet and a few others.

What is the danger of Metformin and iodinated contrast?

Biguanides are known to cause lactic acidosis in patients with a predisposing risk factor. The actual incidence for metformin is, however, quite low and when it has occurred has frequently been in patients with risk factors.

Are there specific patients or risk factors that make it more likely to get a contrast reaction?

Predisposing risk factors for general acute adverse reactions to contrast media are:

Will faster injection rates (5 cc/sec vs. 1 cc/sec) result in an increased incidence of contrast reactions?

"The prevalence of anaphylactoid reactions is not affected by the rate of injection."

Ionic Versus Nonionic Contrast Media: A Prospective Study of the Effect of Rapid bolus Injection on Nausea and Anaphylactoid Reactions.

What are the categories of contrast reactions?

Three Categories:

Mild
Moderate
Severe

Mild Reactions Include

Nausea and vomiting
Cough
Headache
Itching
Flushing
Mild rash or hives

Moderate reactions include

Tachycardia or bradycardia
Hypertension
Hypotension
Dyspnea
Bronchospasm or wheezing
Severe skin rash or hives

Severe reactions include

Laryngeal edema
Convulsions
Profound hypotension
Arrythmias
Unresponsiveness
Cardiopulmonary arrest
Severe reactions are considered life threatening

Who can not get IV contrast material?

The list will vary from site to site but here are some rules of note. Please remember that this list is not complete but a reasonable guide for the user.

What if extravasation does occur? How often are there severe complications?

The good news is that with most contrast extravasations prompt treatment prevents most complications. The literature recently has a few publications that address this issue.

do we treat contrast extravasation when it happens?

Part 1: How do we treat contrast extravasation when it
happens?
Part 2: Is cold compresses the rule or hot compresses?

How do you prevent contrast extravasation?

The key is to anticipate what can go wrong and make sure it doesn’t. it’s the classic risk prevention strategy.

What is contrast extravasation and how often does it occur?

Contrast extravasation occurs when contrast is injected into a vein but goes outside of the vein into the adjacent soft tissues. In most cases this is a mild inconvenience to the patient especially when only a few cc are involved. With larger extravasations (75-100 cc) problems can occur.