How do you figure out which imaging type is best?

[Pachinko]

I just graduated from my FNP program. I think I have a pretty decent grasp of most patho, meds, etc. What I'm less certain about is which kinds of imaging--xray, CT, MRI, etc.--to order for patients.

For instance, I know that bone injuries are best seen with xray, but I'm not sure which views are best. When it comes to something like, say, abdominal pain, I basically just default to what I've seen ordered by my preceptors. I haven't yet come across either a good, comprehensive rule of thumb for selecting which images to do, nor have a found good resource for this info.

Can you help?

[Dembitz, APRN]

I can really only speak to the ortho-type imaging. In the system I use, I choose the body part I want xrays of and it comes with certain standard views. For knees you need to decide weight bearing or non-weight bearing (hint: always weight bearing if possible). For wrists, if you suspect a scaphoid fracture you need to ask for additional scaphoid views. Most ankle injuries should get foot images as well to r/o metatarsal fracture.

I very rarely (once maybe?) order CT scans for musculoskeletal injuries. I order MRIs if I suspect any ligament/tendon damage or disc injuries, almost always after at least a month of conservative treatment. Shoulders can be done with our without contrast (arthrogram -- dye injected directly into joint space, very painful), and I've heard lots of arguments for both (dye better for labral tears and possibly small RTC tears, but advances in MRI technology now show that non-contrast is pretty comparable to contrast). If I'm not sure, I refer to Ortho and let them make the decision.

[Corey Narry, MSN, RN, NP]

What setting are you going to be working in?

My practice is adult critical care and we order a lot of imaging. My rule of thumb is to do a comprehensive history and physical exam, check labs, arrive at differential diagnoses, then proceed with deciding what imaging to use based on the differentials.

In Neuro differentials (altered mental status, seizures, rule out strokes or bleeds, etc), you can never go wrong with ordering a stat non-contrast Head CT and go from there. We have the luxury of a portable Head CT Scanner but the images are not as great as conventional CT scanners in the radiology suite, but they are useful in making emergent decisions when a patient needs to be imaged yet could not leave the unit for reasons such as medical instability.

A Neuro consult always follows and that's usually when further imaging is ordered. MRI's are great for imaging the CNS including spinal pathology. MRI with diffusion weighted imaging are ideal for detecting early or small strokes. Gadolinium is an IV dye used in MRI to enhance images and detect tumors, inflammation, etc. It is nephrotoxic so must be avoided in renal failure.

Cardiovascular differentials (regional wall motion abnormalities, valve disease, RV strain, cardiac shunts, IVC compressibility a surrogate for volume status) are best assessed with an echocardiogram. The ICU has become sophisticated that we have our own ultrasound equipment with a probe that could scan the heart in making swift bedside decisions but we still defer to a formal echocardiogram performed by a sonographer in most cases. TEE's are used to assess valve endocarditis not seen in a transthoracic echocardiogram.

Cardiac CT angios have emerged in the out-patient settings as a way to detect CAD similar to a heart catheterization but they are not covered by insurance and cost about a thousand dollars or more. Again the nephrotoxicity of the contrast dye should be taken into consideration.

Aortic aneurysms and dissections should be imaged with a CT Scan of the chest, abdomen, and pelvis with IV contrast to trace the integrity of the aorta from its origin to where the great vessels emerge, the arch all the way to iliacs. TEE's could see this but given that dissections are oftentimes emergent cases for OR repair, you need to order a CT for a surgeon to decide on taking the patient to OR.

Pulmonary differentials of course start with a CXR. You could see tumors, consolidations, atelectasis, effusions, pneumothoraces, mediastinal silhouettes on these films. Chest CT with PE protocols are used when you are concerned about a PE but should again be used cautiously in patients with kidney injury because of the dye. Alternatively, you could check for LE dopplers to assess for DVT (the usual PE culprit in terms of embolization potential) and an echocardiogram to check for RV strain (which tells you there is likely a clot in the pulmonary circulation). VQ scans are only useful if the CXR is unremarkable. Pulmonologists are usually satisfied with a non-contrast CT of the chest to assess for lung pathology such as interstitial disease, fibrosis, etc.

Nephro differentials can be assessed with ultrasound. Patients who present with kidney failure get a kidney ultrasound to assess for hydronephrosis (which tells you that obstruction is the etiology of the kidney injury). In the out-patient setting, an ultrasound to check for renal artery stenosis is sometimes used to assess HTN in patients if you suspect it.

GI symptoms have the most complex decision tree for me. Whenever I see problems with LFT's (whether hepatocellular vs cholestasis in pattern) a RUQ ultrasound is always a go to. You can see liver masses, gallbladder wall thickening, dilatatation, stones, bile duct obstruction with an ultrasound. A simple KUB can show ileus and detect serious pathology such as abdominal free air which is concerning for bowel perforation. CT scans with oral contrast (Barium vs Gatrografin) will help you in assessing for location and transition point in bowel obstruction. IV contrast is used if you're concerned about tumors, abscesses, inflammation, ischemia. Again, the same caution for IV contrast is used in patients with kidney disease.

That's all I got. Hope others can add some. I always say that when in doubt, you can always call a specialist even if it's just a curbside consult.

I though this was a great article on abdominal imaging from AAFP: http://www.aafp.org/afp/2008/0401/p971.html

[traumaRUs, MSN, APRN]

Juan comes thru once again.

also from nephro standpoint anytime you order contrast be fully aware of their creatinine. Ask about kidney issues. You can use contrast in renal pt but must order it judiciously. If a chronic kidney disease (CKD) pt, consult nephro and may need bicarb prior to contrast to mitigate the potential damage

if you must use gadolinium in dialysis pt, ensure they are scheduled three consecutive days for a fill run of dialysis

[sandnnw, BSN, MSN, EMT-B, APRN]

This will help you:

https://acsearch.acr.org/list

I find it most helpful, the articles are very interesting reading! And, who better to trust than radiologists?

[traumaRUs, MSN, APRN]

Excellent reference, I bookmarked it.

[Julia77]

Thank you for this super thread.

Julia

[Pachinko]

Should have mentioned, I'm an FNP.

AMAZING resource sandnnw.

Thanks to everyone for the feedback.