Requesting scans can be a scary daily occurrence for new doctors. It is one of few times where you liaise directly with a consultant. 

When requesting scans, there are two simple questions you have to ask yourself:

- Why have I been asked to request this particular scan for this particular patient?
- How will it change the management of this patient? 

Usually, most requests are through a computer system. It is important that the information you provide answers the above question succinctly. Include history and examination findings in the ‘clinical information’ section, only if it answers the above question. 

The information you provide is vital for radiologists to modify the request or way the scan is performed to answer the question e.g. with or without contrast & for them to be able to interpret the radiological findings with context. It is also important they protect patients from unnecessary radiation & allocate the resource fairly and in priority order. Therefore ensure you include all relevant details as otherwise, they may have to call you for more information resulting in delays. 

Examples:
Scan: X-ray pelvis and right proximal femur
Clinical information: 87 yr old lady fallen in nursing home today. Non weight bearing on right leg. O/E external rotation of right hip and shortening with bony tenderness – ?right sided NOF # code-box

Scan: CT abdomen
Clinical information: 23 yr old lady, c/o constant acute right LQ abdominal pain since this am. O/E rebound tenderness, guarding, +++pain in RIF, d/c with surgeons, asking for ct abdomen to guide surgical management- ?appendicitis code-box

Urgency of the scan
When requesting a scan, you will be asked how urgent your scan is with drop-down options. (i.e. non-urgent, urgent or emergency). In some situations, you may not know how urgent a scan is, especially if you were asked to do this on a ward round. It is vitally important that you ask a senior if you are unsure about this, as requesting a scan as ‘non-urgent’ for something they need in the next few hours will not make your seniors happy and, most importantly, will delay patient care.

If a scan is needed within the next few hours, normally you need to call the on-call radiologist to inform them that this is needed ASAP. They will then change the order of scans around, according to clinical priority. Whilst on the phone to the radiologist, they will want you to answer the same question and may ask why it is so urgent that you get it done in the next few hours. They normally prioritise scans that will change or inform immediate management, especially if the patient is seriously unwell or is in a life-threatening situation. Think about this when deciding on the urgency of the scan. For example, a CTPA may not need to be done on the same day because the patient will receive the treatment of LMWH anyway. However, if there was a high risk of them bleeding and therefore confirmation was required - the CTPA would be urgent.

Which scan, for what?
Different scanning modalities are better or worse for different things. Here is a rough overview.

Imaging What is it good for? What is it not so great at?
CT Subtle fractures (especially if high suspicion but negative x-ray)
Acute intracranial bleeds & intra-abdominal organs (latter with contrast)
Staging cancer
Will usually miss strokes in the first few hours
Subtle soft tissue pathology, spinal cord compression or osteomyelitis
MRI Soft tissues and organs, spine and spinal cord for compression
Ultrasound Superficial structures, palpable masses, thoracic or abdominal organs, insertion of drains Deep, widespread pathology or bones
X-ray Fractures & bone disease, bowel gas patterns, lung pathology
May miss subtle or early fractures.
May miss subtle findings such as a small mass, effusion or pneumothorax

Ordering scans - restrictions 
In certain hospitals, you may be unable to request certain specific scans if you are a FY1. Ensure you check your local policy to avoid delays.

Contraindications and cautions
When requesting, be aware of certain reasons why different scanning modalities may not be appropriate.

Imaging Some contraindications & cautions
CT & MRI - Require a patient to get into a particular position, keep still & lie flat. May require analgesia/light sedation to achieve this
- Allergies to contrast & whether kidneys can tolerate contrast
- The patient may be too large for the scanner
- Claustrophobia (particularly for MRI which can be quite loud & lasts longer)
CT Pregnancy (relative contraindication), myasthenia gravis, hyperthyroidism/goitre due to iodine contrast
MRI Metallic implants, some artificial heart valves or pacemakers
Some of the above are MRI compatible, have the date and details at hand to ask the radiographer
Ultrasound Difficult if the patient is confused or agitated
Large body habitus can sometimes obscure findings
X-ray Are they able to get into the right position?
Can they sit up and follow instructions to take a deep breath for a chest x-ray?
Pregnancy isn't a contraindication to chest x-rays

When to consider portable scans?
Portable scans include x-ray machines (usually chest x-rays only) and ultrasound scans. Consider whether you're happy for the patient to be out of your sight for 15-30 minutes & with the relative lack of emergency equipment in the imaging department. Thus, they are critical for the unstable patient who might deteriorate. Occasionally, portable x rays are used when a patient’s mobility is severely limited but remember portable x rays are often of lower quality and sometimes repeat x rays are needed.

What to do if a scan is rejected
  • Check or ask why the scan was rejected. Perhaps another imaging modality is more appropriate. Perhaps there is inadequate information.
  • Often it is helpful to ask the radiologist who rejected the scan, what information they need in order to accept it
  • Consider whether your seniors should discuss the scan directly. If the scan is rejected twice they should definitely discuss it directly with you there as this is a great learning opportunity
  • If you really believe the scan should've occurred, focus on why it is important for the safety of your patient
Radiation considerations
Scans deliver different quantities of radiation. It is important to remember this when weighing up the risk of a particular scan vs. benefits. This also supports you having a low threshold for a limb or chest x-ray but relatively higher threshold for an abdominal x-ray or CT imaging.

When explaining risk, it is useful to provide real-world examples for explaining to a patient. Average background radiation dose is roughly 3mSV** per year.

Average effective dose* (mSV) Equivalent natural background radiation Equivalent radiation
X ray of limb 0.001 2-3 hours 1% of chest x-ray
X ray chest 0.1 12 days -
X ray abdomen 0.7 84 days 7 chest x-rays
CT head 2 241 days 20 chest x-rays
CT chest 7 2 years and 3 months 70 chest x-rays
CT abdomen 8 2 years and 8 months 80 chest x-rays
Nuclear imaging or cardiac stress test 40.7 13 years and 6 months 407 chest x-rays

References: 
Written by Dr Rhiannon Jones (FY3)
Reviewed by Dr Vivienne Eze (ST4 Radiology)