Indications/Requests for Radiological Examination

Which examination should you request?

When requesting radiological imaging, important questions to consider are “What do you want to know?” and “Which imaging modality can best answer the question?” Principles for choosing an imaging modality are efficacy of the test, safety, how burdensome the test is, and price. Further, it is important to consider the patients’ age, medical history, current medical condition, and of course that the choice of imaging answers the questions. Sometimes more than one test is necessary. If there is any doubt, always consult a radiologist.

X-ray

X-rays are quick, cheap, nearly always available, and exposes the patient to a relatively minor amount of radiation. Images can provide considerable information in regard to the skeleton, heart, and lungs. This means, for example, that it can quickly provide much needed information in trauma rooms. Through mobile radiography machines, it is possible to perform X-rays examinations in other departments such as the IC. Disadvantages are that soft tissues are poorly imaged, it is a 2D image, and that it uses ionizing radiation.

Examples of indications for X-rays:
Chest X-ray (fig. 1&2): Pneumonia? Metastases? Air trapping? Position of a tube or other lines? Pneumothorax?

Figure 1. Posterior-anterior (PA) Chest X-ray. Multiple pulmonary nodular lesions in a patient known to have lung metastases.

Figure 2. Anterior-posterior (AP) Chest X-ray performed in a trauma room following a high energy trauma. Bilateral pneumothorax, right dorsolateral fracture of ribs 4 and 5 and a midshaft fracture of the right clavicle.

Skeletal X-ray: Fractures, osteoartritis, arthritis
Abdominal X-ray: nephrolithiasis, free air

Figure 3. abdominal X-ray. Extensive bilateral nephrolithiasis

Ultrasound

Ultrasound (US) uses sound waves to create harmless dynamic images (see Ultrasound Technique). It is quick, non-invasive, and nearly always available. US is especially useful for imaging soft tissue and is effective for assessing the abdomen, breast tissue, the scrotum, the neck or the skeletal/musculoskeletal system. It is a dynamic form of imaging where, for example, peristalsis of the intestines, mobility of a structure (e.g. a stone in the gallbladder or inguinal hernia) and compressibility of a structure (e.g. appendix, gallbladder, or veins in the upper or lower extremities) can be seen. See figure 4.

Figure 4. Inguinal hernia (US performed during Valsalva maneuver followed by compression with the probe).

Further benefit comes from the direct contact between the radiologist and the patient. The patient can better indicate the location of the pain and the radiologist can observe pain with pressure from the US probe. There is also the possibility for US-guided injections (e.g. with bursitis) or US-guided biopsies to be performed (e.g. with a suspected liver lesion).
The more superficial a structure is the better it is visualized through US. It is an excellent and safe imaging modality to use for imaging the abdomen in children, adolescents, and adults with low abdominal adiposity. US is less effective in imaging deeper abdominal structures such as the pelvic floor, or regions where bone or air-filled organs may obstruct the image.
Additionally, the quality of an US image is user dependent and saved photos of the scans are often difficult for other doctors to read. The radiologist report in which the findings are described is more important than the saved images, as they serve only to illustrate the findings.

Example US indications:
Abdomen (fig 5&6): Causes of acute abdominal pain (appendicitis, cholecystitis, diverticulitis), hydronephrosis, assessing the size of organs or structures, free fluid after trauma, scrotum if testicular torsion or a testicular tumor is suspected.

Figure 5. Abdominal US. Thickened and layered appendiceal wall with extensive appendicular infiltrate and peri appendiceal fluid; findings supportive of the diagnosis of acute appendicitis.

Figure 6. Testicular US. Testes imaged in transverse plane with color Doppler (left testicle in the image is patient’s right testicle and vice versa). Swollen right testicle with nearly absent color Doppler; Testicular torsion.

Skeleton (fig. 7): arthritis/synovitis, tendon pathologies (ruptures and inflammation), US-guided injections, characterization of a superficial swelling, hip dysplasia.

   

Figure 7. Shoulder US with an image of the footprint insertion of the supraspinatus tendon. A centrally located full thickness rupture of the tendon can be seen. There is a focal loss of fiber structure with accumulation of fluid. Accompanying fluid in the bursa can also be seen.

Veins: Venous thrombosis of upper or lower extremities, aortic diameter.
Cranial: Neonatal transcranial US through the open fontanelles.

CT

Computer tomography (CT) is a technique that, similarly to conventional X-ray, uses radiation (see X-ray/CT Technique). HThe difference is that where a conventional X-ray shows the 2D image, a CT obtains a 3D image of the body. It is a quick investigation where in a few seconds substantial amounts of the body can be imaged. CT images have a high resolution, so small lesions can frequently be seen. In addition, the 3D images can be reconstructed to view the body in different planes and cross sections.
Of all the imaging techniques CT gives the most information on the lung parenchyma. It can be used following an X-ray or inconclusive US. Through use of intravenous contrast, we can further image vascular structures and assess blood flow or perfusion (fig 8).

Figure 8. CT angiography (CTA) of the thorax. Transverse section of an aneurysm of the ascending aorta. Note the dense (white) contrast agent, primarily found in the aorta and less so in the pulmonary artery; in this way the aorta can be properly assessed.

When a CT scan is made the images can be viewed with different settings. With different settings the visualization of the contrast and different structures can be further optimized; the “soft-tissue setting” and “lung window” are frequently used settings (fig. 9a/b). More can be read here in the X-ray/CT technique section..  

Figure 9a. Thoracic CT with IV contrast (in the pulmonary artery). Soft-tissue window; note that the mediastinum, the musculature, and the subcutaneous fat are visualized well. However, the lung tissue cannot be evaluated with the soft-tissue setting.

Figure 9b. This image uses the same scan as in fig. 9a. Lung window; note that the lung tissue can be seen with better resolution. The soft tissue in this setting has less resolution.    

Also, oral and rectal contrast agents can be used to better visualize the intestines, as is used in post-operative investigations.
In pregnant women, CT is relatively contraindicated if the uterus will receive radiation. Due to rapid cell division, the fetus has increased sensitivity to the effects of radiation. Also, with children it is preferred to not use CT due to the radiation exposure (instead, US or MRI is preferred).

Examples CT indications:
Diagnosing/staging malignancies of the thorax/abdomen, after extensive trauma (fig. 10).
Thoracic CT: additional assessment after X-ray, interstitial lung diseases, infections, pulmonary embolism.
Abdominal CT: additional assessment after inconclusive US, infections, abscesses, intestinal perforation or ileus, vessel abnormalities and vessel perfusion/occlusion.
Cranial CT: bleeding or ischemia, after trauma
Skeletal CT: after unclear conventional examination (e.g. in the case of persisting suspicion of fracture or assessing fractured parts in a comminuted fracture). 

Figure 10. Abdominal CT. Liver laceration after trauma (bike handlebar to the abdomen)

MRI

Magnetic resonance imagining (MRI) is a technique that uses a strong magnetic field that is not harmful (see the page on MRI Technique). MRI is based on influencing protons (hydrogen atoms) with a strong magnetic field. MRI provides an image with good contrast between soft tissues, making it possible to characterize soft tissue pathologies. In addition, contrast (non-iodinated) can be given to obtain further information; this is particularly used for the detection and characterization of tumors, metastases, infections, and the imaging of vessels/vascular pathologies (= MR angiography). See e.g. Figure 12.
With MRI you can view organs in multiple planes and axis and unlike CT, it does not use ionizing radiation. Air contains few protons and therefore emits no signal. Air appears as black on MRIs (for example think of the lungs). CT or conventional investigations are therefore more suitable for imaging the lungs.

A disadvantage of MRI is that it takes on average between 20 to 45 minutes to acquire the images. In this time, it is only possible to image a small area of the body (e.g. only the head or focused on an upper abdominal organ). Further, it is expensive and less available than CT scans
MRI is not/less suitable for patients with claustrophobia, patients that cannot lay still, patients with certain foreign bodies (e.g. certain pacemakers, vascular clips in the brain or metal splinters in the eyes).
Heavily obese patients do not fit in the narrow tunnel. Implants such as prostheses are not contraindicated, however they can give strong artifacts locally due to the disruption of the magnetic field.

Examples of MRI indications:

Figure 11. Overview of common MRI indications. HNP = Herniated nucleus pulposus MRCP = Magnetic Resonance Cholangiopancreatography, IBD = Inflammatory Bowel Disease.

Figure 12. Abdominal MRI of a patient with Crohn’s disease in a coronal section. There is wall thickening of the terminal ileum, which shows (on the T1 sequence after administration of gadolinium) reduced diffusion; compatible with terminal ileitis. Read the page on MRI Technique for more information on the various MRI series/sequences.

Writing a good request

If imaging is needed, then it is important that the radiologist has the relevant clinical information to properly interpret the image. Always state the age, gender and relevant medical history (including past operations, illnesses, and malignancies) of the patient. Also state the significant findings from the patient interview in regard to the chief complaint (duration, location, etc.) and relevant findings from the corresponding review of systems. State the relevant findings from the physical examination, laboratory findings, and relevant findings from other complete examinations (e.g. endoscopy). Formulate a clear question so that the radiologist can better understand the clinical picture and what you want to rule in or rule out based on the history, the physical examination, lab findings, and the general appearance of the patient. Abnormalities may resemble each other in radiological images and if the relevant clinical information is not included than there is an increased chance the images will be misinterpreted.

Case 1 (fig. 13) is a 50 yo man with a cough, fever, and a CRP of 140 nmol/L ( 14.7 mg/L). Case 2 (fig. 14) is a 50 yo old man who smokes, has a cough and weight loss, but no fever or increased infection parameters. The images have similarities, but the clinical information helps the radiologist place the findings in the proper clinical context.

Figure 13. Thoracic X-ray. Lobar pneumonia in the right upper lobe.

Figure 14. Thoracic X-ray. Long tumor of the right lower lobe.

Important to note: Do not forget possible allergic reaction to iodinated contrast (especially with CT scans) and make sure to check kidney function if ordering a CT with IV contrast. With MRI requests you must mention the presence of prostheses, pacemakers, etc. and whether the patient is at risk for metal foreign objects in the eye (for example specific professions such as welders). Further, it is important to ask if the patient suffers from claustrophobia.
Make sure that the investigation request remains legible and that it is complete, but also concise. In particular, omit information that is not relevant to the investigation and avoid rare or specialty specific abbreviations.

Example of a proper investigation request:

Clinical Picture:
PMH: 2008 cholecystectomy
HPI: 43 yo man. LRQ pain since yesterday. N/V and LOA present. No measured fever.
PE: RLQ rebound tenderness. Guarding
Labs: Leuk 13, CRP 45. Urine: no abnormalities

Requested Investigation:
Abdominal US

Question:
Appendicitis?
__________________________________________________

Poor example of a request:

Clinical Picture:
64 yo man who presented with liver mets KRAS+ from left sided colonic carcinoma. Patient presents after 6 courses capecitabine/oxiplatin with maintenance therapy (maintenance since August 2016). Good response to date.
Due to HFS, capecitabine has been reduced to 50%. Since initiation of chemotherapy memory disorders have increased. Since April 2017 patient has suffered from diplopia, MRI shows muscle atrophy with no underlying pathology, no mets. Is on a waiting list for strabismus surgery.
In August 2017 from a second opinion from the USA with possibility of surgical treatment. After consultation it was decided to not continue with this. In May 2018 it was discussed that terminating maintenance therapy was an option with the positive course.
However, until now maintenance therapy has been continued on request of the patient. Patient is still responsive to treatment after a year and a half of therapy with capecitabine/avastin. Comes today for the 36th maintenance course. Primary resection after was the 35th treatment.

Question:
Evidence of metastasis? Please compare with CT from Nov 2018.

The request should be as follows:

Clinical Picture:
64 yo man with descending colonic carcinoma and metastasis to the liver. Good response to chemotherapy. Since around 1.5 years maintenance therapy with maintained sensitivity. Recent resection of primary colonic tumor (nov 2018).

Question:
Presence of new metastasis/progression of carcinoma?

 

Authors

Text and Cases:

Dr. J.C. Korving (Abdominal Radiologist at Reinier de Graaf Hospital, Delft)
Dr. A. Srámek (Teaching Physician and Abdominal Radiologist at Leiden University Medical Center)

English Translation:

Chase Neff, MD

Editing and Illustrations:

Drs. A van der Plas (MSK Radiologist at Maastricht University Medical Center+)

30/05/2019. 

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