• 4/F., Champion Tower, 3 Garden Road, Central, Hong Kong
  • Unit. 1908-09, 19/F, Mira Place Tower A, 132 Nathan Road, Tsim Sha Tsui
電腦掃描

Computed Tomography

Generally used to assess head, neck, breast, abdominal and pelvic regions

CT Principle

 

A CT scan uses a narrow X-ray beam operating at a high energy level to capture cross-sectional images of inside organs from many different angles and create a detailed 3D images with advanced computer technology.

 

While CT provides superior image resolution of bony structures, capturing images of soft tissues requires the use of contrast agents for better visualisation. Taking abdominal examination as an example, contrast agent, which blocks X-ray penetration via soft tissues, can highlight the structural organisation of the intestine.

 

It is generally used to assess head, neck, breast, abdominal and pelvic regions. With regards to the surveillance of cancer, CT is commonly applicable for monitoring the lesions in thorax, abdominal and pelvic regions.

 

Below is the information regarding the uses, safety issues, concerns of undergoing a CT examination and its advantages and limitations in comparison with other types of imaging modalities.

CT Uses

 

CT scan has been used in a wide variety of areas, notably for disease detection including cancer, brain lesions such as stroke and abscess, calculi and inflammation, acute bone injury, cardiovascular disease, as well as lung infection and tuberculosis. Also, it is frequently used to guide biopsy, monitor treatment progress and do planning for surgery or radiation therapy.

電腦掃描

CT Safety

 

Radiation

Despite the much higher radiation exposure in undergoing a CT examination compared to general X-ray, the risk of developing cancer from radiation is less than one per 2,000 patients with reference to the information provided by NHS. Reducing radiation exposure without comprising the diagnostic quality of images has been made possible with the team’s effort at our centre.

 

Pregnancy

While the impact of radiation emitted from a CT scan on pregnancy might not be significant, doctors may still suggest having other radiation-free imaging examinations such as Ultrasound or MRI if possible. Female patients should check with their doctor before scheduling the examination if they are pregnant or breastfeeding.

 

Allergy

Less than 1% of patients who are allergic to the contrast agents might experience mild side effects such as itchy skin, nausea, pain over site of injection, shivering and warm sensation. In severe cases, there might be breathing difficulty and hypotension. For patients with severe kidney failure or undergoing hemodialysis, it is possible to develop nephrogenic systemic fibrosis as an adverse reaction to the contrast agents. Death, which might also occur in serious case, is rarely seen. Patients are advised to drink a large amount of water to allow rapid and efficient excretion of the remaining contrast agents out of the body.

Patient safety tips prior to the examination

Diet

Food intake is not allowed for at least 4 hours and only water is allowed before the procedure for some CT examinations.

Health Status

Patients should inform us of any diseases such as renal insufficiency, current medications, history of drug allergy or other health conditions such as pregnancy. For patients having seafood or contrast allergy, premedication should be taken at 12 hours and 2 hours before the procedure.

Diabetic Patients

Patients should inform us of the use of Biguanides, and in case of taking metformin or other medication of the same drug class, patients should not take it on the examination day and within 48 hours after contrast injection. Other medications can be taken as usual.

 

Should there be any issues, radiographers are there to provide as much assistance as possible.

Diagnosis of Cancer|Imaging Tests

 

Common tests for diagnosing cancer includes blood test, urine test, imaging test, biopsy and genetic test. Apart from diagnosing cancer, these investigations can also localise the primary site, differentiate the specific cancer cell type, perform cancer staging, identify whether there is metastasis, formulate treatment plan, monitor disease progression and detect recurrence. Below is the information regarding different tests.

 

超聲波

Ultrasound

Applications:

  • Localize the site of primary cancer
  • Guide biopsy
  • Detect pathological change of tissues and vascular flow

Strengths:

  • No radiation is involved
  • Short examination time
  • Real-time monitoring of change is allowed

Limitations:

  • Low penetration power to deep tissues
  • Low spatial resolution
  • Operator-dependent result
電腦掃描

CT

Applications:

  • Localize the site of primary cancer
  • Detect pathological change of tissues
  • Guide biopsy
  • Allow cancer staging
  • Formulate treatment plan
  • Evaluate treatment effectiveness
  • Detect recurrence

Strengths:

  • Short examination time

Limitations:

  • Radiation is unavoidable
  • Relatively low spatial resolution for soft tissue structures such as muscle and nerve
  • Risk of contrast allergy
正電子掃描

PET-CT

Applications:

  • Localize the site of primary cancer
  • Detect pathological change of tissues
  • Guide biopsy
  • Allow cancer staging
  • Predict prognosis
  • Formulate treatment plan
  • Evaluate treatment effectiveness
  • Detect metastasis or recurrence

Strengths:

  • High sensitivity in picking up cancer at early stage
  • High accuracy

Limitations:

  • Radiation is unavoidable
  • Injection of radiotracers is needed
  • Might not be suitable for diabetic patients
磁力共振

MRI

Applications:

  • Localize the site of primary cancer
  • Detect pathological change of tissues
  • Differentiate benign tumor from malignant cancer
  • Formulate treatment plan (i.e. localisation for surgical planning or radiation therapy)
  • Monitor treatment progress
  • Evaluate treatment effectiveness
  • Detect recurrence

Strengths:

  • No radiation is involved
  • Better image resolution for soft tissue structures such as muscle and nerve
  • Multi-planar 2D and 3D images are available
  • Contrast allergy is rare

Limitations:

  • Metallic object is contraindicated in a MRI suite
  • Risk of claustrophobia
  • Long examination time

Related Articles

Our Screening Service

  • MRI
  • PET-CT
  • CT
  • 3D Mammography
  • Ultrasound
  • X-Ray
  • Blood Test