HO / MO guide to radiological investigations
Ver 60430


  • Organisational chart of imaging departments
       - Important people in the department
  • Pre-investigation preparation
       - Contraindications
       - Preparation
       - Consent Taking and Risks of procedure
  • Radiological investigations
       - FAQ
       - Head And Neck / Neurology / Neurosurgery / ENT
       - Respiratory / Cardiology / Cardiothoracic Surgery (CTS)
       - Abdomen / Pelvis / Gastroenterology / HBS / Urology / Obstetrics / Gynaecology / Breast
       - Orthopaedics / Spine / Extermities / Trauma
  • Disclaimer

  • Start

    Organisational chart of imaging departments (aka Which department do I arrange this scan with?)
    Imaging Department Organisational Charts - Nuclear, Diagnostic and Therapeutic Radiology

      However, most of the hospitals don’t have all three departments. For some scans, they will be done by the radiology department; for others, the patient will have to travel to another hospital.
      In addition, the radiology departments in larger hospitals separate their inpatient and outpatient locations (E.g. SGH Inpatient is Blk 6, but outpatient is Blk 2)

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    Important people in the department (aka Who do I look for?)
      Who is he? His role When you need to look for him!
    Radiologist Medical doctor specialising in imaging
  • Approve xray requests
  • Urgent requests
  • “Protocols” (gives technical instructions) on how to do the scan.
    Doesn’t actually do most scans! (except fluoro, U/S and angio)
  • Not sure which investigation (e.g. CT vs MRI), special circumstances (pregnancy, implants in MRI, post-op anastomotic leak)
  • Covers medical emergencies.
  • Allergic reaction, collapse, resus
  • Interprets scans and issues report.
  • Urgent report, second opinion
  • X-ray conferences
  • Submit list of cases for round
  • Radiographer Technologist who runs the xray machines(Diploma holder after ‘A’-level)
  • Person who actually performs the xray, CT or MRI
  • If you’ve brought the patient down and can’t find anyone!
  • Prints the xray films
  • Need hardcopy film or CD
  • Sonographer Specialised radiographer that does ultrasound
  • Specialises in ultrasound
  • -
    Clerk Runs the front desk!
  • Receives your request form
  • Check if form has been received
  • Schedules appointments
  • Check appointment date and ask for an earlier one (sometimes works!)
  • Issues instruction phamplets, oral contrast, etc.
  • Collect contrast/prep after urgent request is approved
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    Pre-investigation preparation

    Contraindications(By modality)


    Absolute C/I

    Relative C/I

    Plain Xrays
  • Pregnancy
  • i/v contrast:
  • Allergy: CT Contrast, Iodine, Fish
  • Renal disease (Raised Cr)
  • Asthma
  • DM on metformin
  • Allergy: Multiple(> 3)
  • Ultrasound - -
  • Cochlear implant
  • Pacemaker
  • Intraocular foreign body
  • Other mobile ferrous objects
  • Depending on model/operation date
  • Vascular clips
  • Artificial heart valve
  • Barium swallow /
    meal / enema
  • Suspected perforation / leak
          (use water-soluble contrast)
  • Acute Intestinal obstruction
  • Patient unable to stand/weight bear
  • Patient unable to turn over

  • Preparation (By modality)


    Fasting (8 hours)*


    Plain Xrays No  
    Mammogram No Ideally in first 14 days of menses
    (will be arranged by the appt desk)
    Ultrasound For HBS and renal arteries  
    Barium swallow / meal Yes  
    Barium enema Yes, overnight Bowel preparation 1-2 days before
    IVU Yes Bowel preparation 1-2 days before
    CT abdomen &/or pelvis Yes May require oral contrast 1-2 hours before
    MRI For liver, MRCP  
    *- Implication: Keep the patient nil-by-mouth if you think you need the scan urgently!    

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    Consent Taking and Risks of procedure

    When is written consent required?
    Varies between hospitals, but in general:
    1. Age < 21
    2. Pregnant women
    3. Women who have missed their period, or are in 2nd half of cycle (for high dose Ix)
    4. All interventional procedures (including biopsy)

    Radiation dose
        Risk from radiation is a slope, there is no one “cut-off” point below which it is “perfectly safe” - even small radiation doses may have some risk. Therefore, statutory regulations require the dose to be “as low as reasonably achievable”.
         Having said that, there is no absolute “legal” limit to the dose a patient can receive - go ahead and order the scan if you think the investigation is medically indicated, and the benefits outweigh the risk.
         What then, is the risk, and how do you explain it to patients in layman terms?
    Modality / Procedure Equivalent of “normal”
    daily background radiation
    Risk of fatal cancer / death
    Xray – Limbs 1 day 0.0001% (1 in a million)
    * Eating 2 bananas a week for 1 year 1 day  
    Xray – CXR 3 days 0.0003%
    Xray – Skull 9 days 0.001% (1 in 100,000)
    * Smoking 1 pack of cigarettes - 0.001%
    * Flight from Singapore to New York 1 month  
    Mammogram 2 months 0.005%
    Xray - Abdomen, Pelvis, Spine 4 months 0.01% (1 in 10,000)
    Tc-99m thyroid scan 6 months  
    IVU 1 year 0.03%
    Barium swallow, meal, follow-through 1 – 1.5 years 0.03%
    CT Head 10 months 0.03%
    Tc-99m dynamic cardiac scan 2 years 0.05%
    CT Chest, abdomen or pelvis 3.5 years 0.1% (1 in 1,000)
    * Dying in a home accident each year - 0.1% (1 in 1,000)
    * Smoking 1 pack of cigarettes a day x 1 year - 0.35%

    i/v contrast   (IVU and CT scan)
    (1) Allergic reaction / anaphylaxis
      -  Idiosyncratic, just like all other drugs
      -  Increased risk if (1)Multiple drug allergies  (2)Recent asthma (<1 year ago)
      -  Prevention: Steroids given AT LEAST 12 hours before the scan.
        -  Examples are : Prednisolone 20mg the night before and on the morning of the scan.
        -  In emergencies: Hydrocortisone i/v 200mg q4h starting at least 6 hours before the scan.

    (2) Extravasation
      -  Definition: When the contrast is forced outside the vein
      -  Background: About 50mls of contrast (which is as viscous as D50%) is injected as fast as 5mls/second under great pressure
                           (If you don’t believe, get a 20ml syringe, some D50%, a blue plug, and see if you can inject everything out in 5 seconds!!).
      -  Problem: Vein bursts (damn, got to reset the plug ;-) --> Contrast leaks out into tissue --> Draws water from surrounding tissues
                           --> (1)Dehydration (& cell death)of surrounding tissues  and (2)Compartment syndrome
      -  Prevention:
                 -   i. Make sure plug works(They check, and you’ll just have to walk down to the department to re-set it if it doesn’t work)
                 -   ii. Large bore (Pink/Green) plug for procedures requiring high-injection rates (generally anything vascular/arterial).
                 -   iii. If all else fails, blue plugs (but not in tiny finger veins!) may be acceptable for slow-injection rates (e.g. brain)
                 -   iv. PICCs are NEVER acceptable. (1) The tiny tip can blast off into the pulmonary arteries and (2) SVC rupture is not a pretty sight.
      -  Treatment:
                 -   i. RICE (Rest, Ice-pack, Compress, Elevate extremity)
                 -   ii. Watch for compartment syndrome, especially if large volume

    (3) Contrast induced nephrotoxicity
      -   Defined as a 25% increase in serum creatinine (does not always require dialysis though).
      -   1% in low risk patients
      -   10% in high risk patients (Diabetes, CCF, renal impairment, nephrotoxic drugs, age > 70yrs)
      -  Prevention:
                 -   i. Any high risk factors: Pre-hydrate patient
                 -   ii. Renal impairment: Consider N-acetylcysteine (600mg bd x 2 day before and on day of scan)
                 -   iii. Space out contrast studies 72h apart, if possible (e.g. cancer staging)
                 -   iv. Consider non-contrast CT or alternate studies (e.g. US, MRI)
      -   Paradoxically, patients whose kidneys have already failed and are on dialysis can ignore all the above.

    (4) Metformin-induced lactic acidosis
      -   Metformin: Stop on the day, and 2 days after the scan.
      -  Once again, do this proactively, if you think patient might be going for a contrast-CT soon!
          (Just don’t forget to convert to insulin/another OHGA, and to re-start it later!)

    (5) Breast feeding
      -   Can scan as per normal, but no breast feeding x 24h after the scan

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    Radiological investigations


    Q: How do I know which scan to order?
    A: Specifying the modality(i.e. CT, MRI), organ of interest and including an adequate history is usually enough. For example, “CT lung” for “Lung cancer” vs “PE” vs “Interstitial lung disease” will get you three different scans, but as long as you include the diagnosis/history, there is no need to specify the exact technical details. Even suspected clinical diagnosis or the clinical indication, no matter how silly (e.g. “Hemoptysis for Ix”, “right sided rib pain”, “TB x 40 years ago”).

    Q: What do I write in the “History” column?
    A: The keyword is “relevant”. Include whatever you think might be relevant to the scan, such as Presenting complaint, Duration, Possible causes (e.g. TB, prostate cancer), Physical findings/relevant investigations (e.g. axillary LN, pyloric ulcer on OGD, Hep B carrier), Treatment so far (e.g. Subtotal gastrectomy on 21/4/06), and any previous scans (e.g. U/S Feb 06: 4cm liver mass). Also, include any questions your consultant had (e.g. ?increase in size since 2004, ?anastomotic leak) so that they can be specifically answered in the report (Which may well save you a trip down to bug an irritated, overworked radiologist!).

    Q: That’s a lot to write! What can I leave out?
    A: More is better than less, especially if you’re unsure! (It’ll save you an angry phone call from the radiologist, or even worse, having to explain to the patient why he needs another $350 CT scan of the same organ when he just had one yesterday, and to the consultant why the scan didn’t include the pelvic anastomosis…). But you can safely leave out irrelevant comorbidities (e.g. schizophrenia in a liver scan), and a summary of the history/physical exam is enough (e.g. “R breast lump x 2/12” vs “Admitted for # NOF. Incidental finding of R breast lump, 4.5cm, hard. L breast NAD. etc. etc.)

    Q: Does the scan require i/v contrast (a.k.a Do I need to set a plug)?
    A: This is a tricky one. The full list is given below, but in general, the following require contrast:
  • Most CT scans, including those looking at/for:
          -  Tumour
          -  Inflammation
          -  Blood vessels
  • Some MRI scans, especially those looking at
          -  Tumour
  • All interventional studies (except PermCath and Hickman lines, but including PICC lines)
    Common scans that do NOT require i/v contrast include:
  • CT head for stroke, trauma
  • CT spine and extremities for trauma
  • CT KUB for renal/ureteric stones

    Q: How do I arrange for an “urgent” scan?
    A: This varies by hospital, but here is a suggested approach:
    Arranging urgent x-ray(xray) investigations scans

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    Xray: Skull
    Indication Investigation
    Vault # Skull (AP,Lateral, Towne’s)
    Maxilla # Skull (AP, Lateral, OM)
    Mandible # Mandible X-xray
    Orbit # Orbit X-ray
    Orbital foreign body Orbit X-ray + Look up/down views
    Sinusitis (chronic) X-ray Paransal sinuses

    Xray: Non-Skull
    Indication Investigation
    FB Throat Neck xray,lateral (not C-spine)
    Cervical spine trauma C-spine xray (not Neck)
      +/- Swimmer / Lat pull-down for C7/T1
    Parotid stone Parotid xray (occlusal view)
    Dental Occlusal / OPG

    Indication Investigation
    Swallowing assessment / ?Aspiration (1)VFS if high % aspiration
    (2)Barium swallow (not gastrograffin)
    FB throat / perforation / post-esophagect (1)Gastrograffin swallow
    (2)NB: CT neck better for FB
    Nasolacrimal duct stenosis Dacrocystogram*
    Salivary/Parotid duct stenosis Sialogram*
    * - Specialised, rarely performed investigation

    Indication Investigation
    Thyroid lump / goitre U/S thyroid
    Young CVA U/S carotids

    Indication Investigation Contrast?
    Stroke, hemorrhagic Head injury (see NICE criteria) CT brain No
    Meningitis CT brain Maybe
    Fits, brain tumour, mets CT brain Yes
    Chronic sinusitis CT paranasal sinuses No
    Hearing loss, conductive CT temporal bone No
    Foreign body throat CT neck Maybe

    Indication Investigation Contrast?
    Stroke, hyperacute (< 12 hours) MRI brain (stroke protocol)
    NB: CT is better to exclude bleed
    Stroke, brainstem Posterior fossa lesions MRI brain (more sensitive than CT) Maybe
    Hearing loss, sensorineural MRI IAM / MRI IAM screening Yes
    Retrobulbar mass, orbital tumor MRI orbits Yes

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    Chest X-ray
    Indication Investigation Which side?
    Basic CXR view CXR (Erect)  
    Rib # CXR (Oblique) Same side as suspected # i.e. R oblique for R  #
    Localise lung lesion CXR (Lateral) Same side as lesion
    Loculated effusion,    or patient cannot sit up CXR (Lateral decubitus)   Same side as effusion i.e. R LD for R effusion
    Small pneumothorax,    or patient cannot sit up CXR (Lateral decubitus)  

    Opposite side of pneumothorax i.e. R LD for L pneumothorax
    Sternal # Sternal Xray  
    General notes on CXR:
  • The ‘standard’ CXR view is PA erect, but patient must be able to stand, and it cannot be done portable. AP Sitting is second best, followed by Supine.
  • Lateral views are not routinely required. Ask yourself – “how will it affect management?”

    Indication Investigation
    Diaphragmatic paralysis Fluoroscopic sniff test*
    * - Specialised, rarely performed investigation  

    Indication Investigation Contrast
    Most lung conditions CT Thorax / CT Chest  
    Interstitial lung disease High resolution CT (HRCT)  (NB: Slices are “skipped” – do not use for tumour detection) No
    Aortic aneurysm / dissection CT Aortogram / CT Thoracic aorta Yes (High rate)
    Pulmonary embolism (PE) CT PE / CT Chest (PE protocol) Yes (High rate)
    Coronary arteries CT Coronary Arteries / Cardiac CT Yes (High rate)

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    Abdomen X-ray
    Indication Investigation
    Standard AXR view AXR (Supine)
    Air-fluid levels AXR (Erect) or (Lateral decubitus)
    Free air under diaphragm CXR (Erect) or (AP Sit)
    Ureteric/bladder calculi KUB
    General notes on AXR:
  • The ‘standard’ AXR does not always cover the pelvis. Order a KUB for pelvic pathology.
  • Erect or decubitus views are not routinely required, even in IO. The supine view shows bowel distribution better, and free gas is better detected on the CXR.  

    Indication Investigation Preparation Notes
    Liver, gallbladder U/S liver / HBS Fast x 8 hours Includes a quick look at kidneys
    Kidneys U/S kidneys -  
    Kidneys & bladder U/S kidneys + bladder Needs to have a full bladder Not routinely ordered
    Renal arteries U/S renal artery Fast x 8 hours Specialised investigation
    Aorta U/S abdominal aorta Fast x 8 hours CT preferred, if possible
    Uterus/ovaries U/S pelvis Needs to have a full bladder May include endovaginal scan
    Testes U/S testes -  
    General notes on ultrasound:
  • Do NOT order "ultrasound abdomen" – only solid organs can be scanned, and the vast majority of the “abdomen” (including the bowel) is un-scannable.
    You will either get a rejected request, a call from an irate radiologist, or a vague scan of the region based on the clinical history in your form.
    They will never scan the entire “abdomen”, so you might as well be more specific.

    Intravenous urogram (IVU)
    Indication Investigation Preparation
    Hydronephrosis, ?stones IVU Fast overnight, bowel prep
    General notes on IVU:
  • IVU as an inpatient is usually suboptimal due to (1)poor bowel preparation or (2)infeasible to keep patient in hospital just for bowel prep.
    Alternatives include CT KUB (if looking for hydro and stones, or if renal function is poor) or CT urogram (if looking for renal function or pyelonephritis).
    Disadvantages of CT are higher cost and radiation dose.    

    Indication Investigation Requirements Notes
    Esophagus / swallowing problem Barium swallow Be able to stand  
    Stomach / PUD / reflux / hiatus Barium meal Be able to stand and roll over.  
    Small bowel pathology Barium follow-through    
    Enteroclysis   More invasive than follow-through, but better results
    Large bowel Barium enema Be able to stand and roll over. No fecal incontinence.  
    ?anastomotic leak Water-soluble / gastrograffin swallow/ meal/ enema. As for similar barium study. Include op details (incl anastomosis type), and exact date study is required on form.
    Urethral stricture Ascending urethrogram   Include op details if any
    Vesico-ureteric reflux MCU   Include op details if any
    Post PCN Check nephrostogram    

    Indication Investigation Contrast
    Upper abdominal pathology CT abdomen Yes
    Pelvic / gynae pathology CT pelvis Yes
    Entire abdominal cavity required CT abdomen + pelvis (abdo/pelvis) Yes
    Liver (Routine e.g. abscess) CT liver Yes
    Liver lesion ?HCC CT liver (triphasic) Yes (High rate)
    Liver HCC post-TACE CT liver (plain + triphasic) Yes
    Pancreas CT pancreas (fine cuts) Yes
    Renal /ureteric stone CT KUB (may differ by hospital) No
    Kidneys CT kidneys Yes (High rate)
    Kidneys, ureter, bladder CT urogram(may differ by hospital) Yes (High rate) and Lasix
    Abdominal aorta CT abdominal aorta Yes (High rate)
    Colon CT colongraphy Yes and rectal gas
    General notes on CT:
  • There are many, many different CT protocols for the abdomen (e.g. see CT liver above!). If unsure, it is best to state the organ of interest, and provide sufficient history, rather than guess blindly.
  • Abdomen and Pelvis (in radiological protocol terminology) are completely different!! Your consultant may casually order a “CT abdomen” for “?sigmoid CA” or “abd pain for ix”, when what he really means is “CT Abdomen + Pelvis”. The radiographers protocoling the scan are not medically qualified, and may or may not catch your meaning, so make sure you fill the form in correctly!  (As an aside, the main reason why the pelvis is not automatically included in a “CT abdomen” is due to the high radiation dose to the gonads and bowel.)
  • Almost all abdo scans require fasting. If you’re clerking a patient and think he might need an urgent scan, keep him NBM!  

    Indication Investigation Contrast
    Liver MRI liver Yes
    Bile duct stones MRCP Maybe
    Pancreas MRI pancreas Yes
    Kidneys MRI kidneys Yes
    General notes on MRI:
  • There are many, many, many MRI protocols for the abdomen, even more than for CT. MRI liver for HCC alone has 12 sequences. Don’t bother trying to specify them, just state the organ of interest, and provide sufficient history.

    Indication Investigation Note
    Screening Mammogram  
    Evaluation of breast lump Ultrasound + Mammogram  
    Biopsy of lump Ultrasound guided bx Specialised investigation
    Biopsy of lesion on mammogram Mammotome / Stereotactic biopsy Specialised investigation
    Implant rupture MRI breast Specialised investigation

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    General notes on orthopaedic xrays:
  • Othopaedic xrays are really easy to order – if you can name the bone that is likely to be fractured, then that's the xray you ask for! So go ahead, and order xrays according to where you think the problem is.
  • Using radio-opaque markers, especially for foreign bodies, is highly recommended. If you can’t personally accompany the patient and put the marker – just write a “with marker” on the xray form, and make sure the patient  can point out the site of the problem!

    Plain x-rays
  • See head and neck

  • Cervical spine
  • Cervical spine (Swimmers view) or (Lateral pull-down)
  • Open-mouth / Odontoid views
  • Thoracic spine
  • Lumbar spine
  • Oblique views of above
  • Coccyx  

    Upper limb
  • Clavicle
  • Scapula
  • Shoulder
  • Humerus
  • Elbow
  • Forearm or radius/ulna
  • Wrist
  • Scaphoid
  • Hand
  • x finger

  • Pelvis (AP)
  • Pelvis (Inlet / Outlet)
  • Judet views (for acetabulum)

    Lower limb
  • Hip
  • Femur
  • Knee
  • Skyline (Patella)
  • Tib/Fib
  • Ankle
  • Calcaneum
  • Foot

  • CT / MRI for tumour or trauma
  • Specify region as above.
  • 3D-reconstructions are not performed by default at most hospitals, so specify if your consultant needs them.

    Indication Investigation
    Rotator cuff pathology U/S shoulder
    Carpal tunnel, cysts, neuroma U/S wrist
    DDH / CDH (< 4-6 mths) U/S hip

  • Spine (specify region, level, and side of symptoms)
  • Shoulder*
  • Wrist*
  • Hip
  • Knee
  • Ankle
  • General notes on MRI:
  • While MRI is highly detailed, it is not cheap, and before ordering one, ask yourself if it will affect subsequent management.
  • * - These procedures may involve use of intra-articular contrast injection (arthrogram), which depends on indication for the scan, and varies between hospitals. Once again, include all relevant details on the request form (esp. suspicion of tears and any previous operation) and advise patient he may require an injection.    

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