So, you’re at the hospital. You’re worried about the medical emergency that has landed you there. The doctor is not saying much but has ordered some imaging tests such as a chest X-ray and CT scan.
Or you could be scheduled for a mammogram in a week’s time and you’ve just remembered the dental X-ray you got recently. In another scenario, you might be asked to take a PET scan after your annual health check turned up something suspicious.
If you’ve been in one of those situations before, you might have wondered: Can you be exposed to too much radiation? Will it cause cancer? Is there a need to speak up even if you’re not pregnant?
“The amount of radiation used each time varies significantly,” said Associate Professor Lionel Cheng, a senior consultant and the head of Singapore General Hospital’s Department of Diagnostic Radiology.
Basically, it comes down to the type of imaging test used. For instance, the typical amount of radiation emitted during an X-ray, bone density scan or mammogram is lower than the levels emitted during a CT scan or PET scan, said Assoc Prof Cheng.
(Photo: iStock/mdisk)
A simple X-ray of the teeth, chest or limbs carries a negligible 1 in 1,000,000 radiation risk, according to Parkway Health Radiology. Or the equivalent of exposing yourself to a few days of background radiation. Yes, you are bathed in the natural and inescapable radiation from the environment such as the ground, air, building materials and cosmic rays from outer space.
Even the so-called “higher” radiation from a CT scan or PET scan only carries a low risk of causing cancer, according to Parkway Health Radiology – 1 in 10,000 to 1 in 1,000, to be exact or the equivalent of a few years of exposure to natural radiation.
The area being imaged (for example, an arm versus the entire body) and duration of the imaging process also determine the amount of exposure, said Assoc Prof Cheng.
“There is no specific number of scans that is the upper limit for patients,” said Assoc Prof Cheng. “Some patients with complicated or urgent conditions have multiple imaging studies done in a short span of time. Others may only have one or two scans done over a few years.”
Rather than focusing on a specific number, he said, “it is more important for patients to tell their doctors if they have had other scans done recently”.
(Photo: iStock/SARINYAPINNGAM)
If you’ve had scans done at a polyclinic or public hospital before, your doctor would be able to access those records from the public healthcare system – and reduce duplicating tests and schedule appropriate follow-up scans at the correct time, said Assoc Prof Cheng.
However, “scans done in the private sector or overseas will not be in the clinical notes of the doctor, so it is important for patients to provide such information”, he continued. “The doctor can then take this into account when considering any other medical imaging test.”
Sometimes, “a single scan does not provide sufficient information for an accurate diagnosis”, said Matthew.
“Using multiple imaging modalities allows for a more comprehensive assessment, ensuring precise diagnosis, effective treatment planning, and thorough monitoring of a patient’s condition.”
(Photo: iStock/Wavebreakmedia)
For instance, an X-ray may help doctors detect bone fractures sustained in an accident but it can’t check for internal bleeding and organ damage, which a CT scan and MRI scan can, said Matthew. She cites more scenarios below where multiple imaging tests may be necessary:
Speak up if you're pregnant. Otherwise, modern X-ray equipment restricts the beam size only to the area that needs to be imaged, said the American Dental Association (ADA), so there isn’t a need for protection such as a thyroid collar against extraneous exposure to radiation.
Following ADA’s guidelines, local dentists such as Dr Andrew Chia from Vista Dental Surgery, also do not use thyroid collars as they “can inadvertently block the X-ray beam, which spoils the image”. “The X-ray will need to be retaken,” he said.
“When this happens, more radiographs need to be taken and unnecessary X-rays are what we want to avoid,” said Professor Purnima Kumar, who chairs the Department of Periodontology and Oral Medicine at the University of Michigan School of Dentistry as well as the ADA Council on Scientific Affairs.
Collapse Expand
Why do you sometimes get a CT scan and not an X-ray? Is the radiation from a mammogram higher than a regular X-ray? We find out:
1. X-RAY
What is it: It uses a form of electromagnetic radiation with high energy to capture detailed images of body structures, said Betty Matthew, a senior principal radiographer from SATA CommHealth. “Since X-rays involve ionising radiation, exposure is carefully controlled and limited.”
Dr Lee Chau Hung, a senior consultant from Tan Tock Seng Hospital’s Department of Diagnostic Radiology, added that X-rays have “a very low radiation dose” and are a “suitable imaging test across all ages and genders”.
When is it used: Typically for detecting fractures, joint dislocations, lung infections such as pneumonia, and certain abdominal conditions, said Matthew.
Who isn’t suitable: Pregnant women as the emissions may harm the development of the foetus. Otherwise, “there are no absolute exclusions for X-ray imaging”, said Matthew. Still, an X-ray is not ordered indiscriminately and “is only recommended when the benefits outweigh the risks”, she said.
2. COMPUTED TOMOGRAPHY (CT SCAN)
What is it: You might associate it with a large, doughnut-like scanner. It emits multiple X-ray beams to produce three-dimensional images of your insides, explained Dr Lee.
When is it used: “It is very useful in providing a detailed visualisation of almost all internal organs.” And with recent technology, you can be scanned from head to toe in just one breath hold or less than 20 seconds, said Dr Lee.
(Photo: iStock/Edwin Tan)
Who isn’t suitable: It requires the highest amount of radiation and is usually avoided in children, pregnant women and young adults, unless absolutely necessary, said Dr Lee.
Also, if you have asthma, allergies or renal impairment, you may not be suitable for a CT scan. A dye or contrasting agent needs to be injected prior to the scan, said Dr Lee, and you may react to the dye.
But it’s not a hard “no” as steroidal medication may help to reduce the risk of an asthma attack or an allergic reaction. Otherwise, an alternative imaging test may be advised for them instead, he said.
3. MAGNETIC RESONANCE IMAGING (MRI)
What is it: This also has a large, ring-like scanner but you'll spend more time in it than the CT scanner. It generates electromagnetic waves to obtain “very detailed three-dimensional images of the internal organs”, according to Dr Lee, and has the "highest resolution among all the imaging tests". But it is also one of the most expensive, he said.
“As no radiation is involved, it is preferred over CT for children and young adults. With recent technology, MRI scans are also safe in pregnancy,” said Dr Lee.
Like CT scans, a dye or contrasting agent is injected to visualise the internal structures more clearly, said Dr Lee. “Newer MRI contrast agents are very safe and can even be used in patients with renal impairment.”
(Photo: iStock/zorazhuang)
When is it used: It is usually reserved for very specific scenarios, said Dr Lee. For example, doctors use it to look for nerve compression in the spine, small tumours in the liver and limbs, or small structures such as the urinary tract and bile ducts.
Who isn’t suitable: Not for patients with claustrophobia or those who can’t keep still and follow certain breathing patterns, said Dr Lee. That’s because it takes a very long time to obtain the images. For example, an MRI scan of the lower back takes about 15 to 20 minutes, he said, while the liver can take up to 30 minutes.
“Most importantly, because MRI requires the use of high-intensity magnetic waves, it may not be safe for patients with metal implants such as clips, staples, heart stents or metallic foreign objects as they may get heated or even move within the body,” he clarified.
3. ULTRASOUND
What is it: You would have watched enough TV to associate ultrasound imaging or sonography with babies in the womb. And for good reason: “It is a safe and widely used diagnostic tool that does not involve radiation,” said Matthew.
“Instead, it uses high-frequency sound waves to create real-time images of internal organs and blood vessels,” she said. To obtain the images, a gel is applied and a small device is placed on the area of interest such as the abdomen or back to take pictures of the various organs underneath.
(Photo: iStock/Pitchayanan Kongkaew)
When is it used: Ultrasound is commonly used in obstetrics and gynaecology to monitor foetal development as well as for assessing various medical conditions, according to Matthew.
“It is ideal for soft tissue evaluation, including monitoring pregnancy, assessing abdominal organs, detecting gallstones, and examining blood flow in blood vessels. It is also used for guided procedures such as biopsies,” she said.
Who isn’t suitable: Ultrasound can’t penetrate bone and won’t be able to show what lies within, according to Singhealth.
It also cannot pass through air such as intestinal gas, so an evaluation of the stomach, small intestine and large intestine may be limited. Deeper body parts such as the pancreas and aorta may also be limited, especially if the patient is obese, because body tissue weakens the sound waves the deeper they pass into the body.
4. MAMMOGRAM
What is it: Put simply, it is a specialised X-ray of the breasts. “It can identify abnormalities in the breast before symptoms appear, significantly improving treatment outcomes,” said Matthew.
The scan itself is actually very fast, typically a few seconds, according to Dr Lee. “However, time is needed to position the breast to obtain the best images and this may take an additional 5 to 10 minutes, depending on how many extra images are needed.”
“Also, as compression on the breast tissue is needed,” he highlighted, “it can be a little bit uncomfortable for the patient.”
(Photo: iStock/andresr)
When is it used: Other than regular screening, “mammograms are also used for individuals experiencing symptoms such as lumps or breast pain to detect any abnormalities”, said Matthew.
Who isn’t suitable: Because radiation is used, this test is avoided in young women until they reach the recommended age for screening, said Dr Lee.
5. BONE DENSITY SCAN
What is it: “This is a very special type of scan that uses X-rays to determine bone strength,” said Dr Lee. The hip or wrist is usually scanned and it takes just a few minutes to position the body part and perform the scan, he said.
When is it used: “This test is usually performed for elderly patients who are more prone to osteoporosis. However, young patients may be required to undergo this test if they are on certain medications that may affect bone density," said Dr Lee.
Who isn’t suitable: Pregnant women as radiation is involved. Those who have undergone recent major spinal surgeries and individuals with severe spinal abnormalities such as scoliosis are also excluded as the results might be inaccurate.
(Photo: iStock/Mindful Media)
6. POSITRON EMISSION TOMOGRAPHY (PET SCAN)
What is it: This is a highly specialised scan of the whole body, according to Dr Lee. “A special radioactive dye is injected and the patient lies in a scanner, which detects the dye as it is absorbed by different organs.”
He highlighted that the process takes about two to three hours in total because the dye takes time to be absorbed by the different organs before the scan is performed.
When is it used: The main use of this scan is for the detection of cancer and cancer spread, but it can also be used to look for a source of infection, said Dr Lee.
Who isn’t suitable: This scan is usually avoided in children and pregnant patients as there is radiation involved, said Dr Lee.
Continue reading...
Or you could be scheduled for a mammogram in a week’s time and you’ve just remembered the dental X-ray you got recently. In another scenario, you might be asked to take a PET scan after your annual health check turned up something suspicious.
If you’ve been in one of those situations before, you might have wondered: Can you be exposed to too much radiation? Will it cause cancer? Is there a need to speak up even if you’re not pregnant?
HOW MUCH RADIATION ARE YOU EXPOSED TO?
“The amount of radiation used each time varies significantly,” said Associate Professor Lionel Cheng, a senior consultant and the head of Singapore General Hospital’s Department of Diagnostic Radiology.
Basically, it comes down to the type of imaging test used. For instance, the typical amount of radiation emitted during an X-ray, bone density scan or mammogram is lower than the levels emitted during a CT scan or PET scan, said Assoc Prof Cheng.
(Photo: iStock/mdisk)
A simple X-ray of the teeth, chest or limbs carries a negligible 1 in 1,000,000 radiation risk, according to Parkway Health Radiology. Or the equivalent of exposing yourself to a few days of background radiation. Yes, you are bathed in the natural and inescapable radiation from the environment such as the ground, air, building materials and cosmic rays from outer space.
Even the so-called “higher” radiation from a CT scan or PET scan only carries a low risk of causing cancer, according to Parkway Health Radiology – 1 in 10,000 to 1 in 1,000, to be exact or the equivalent of a few years of exposure to natural radiation.
The area being imaged (for example, an arm versus the entire body) and duration of the imaging process also determine the amount of exposure, said Assoc Prof Cheng.
IS THERE A CAP TO THE NUMBER OF SCANS YOU CAN UNDERGO A YEAR?
“There is no specific number of scans that is the upper limit for patients,” said Assoc Prof Cheng. “Some patients with complicated or urgent conditions have multiple imaging studies done in a short span of time. Others may only have one or two scans done over a few years.”
Rather than focusing on a specific number, he said, “it is more important for patients to tell their doctors if they have had other scans done recently”.
(Photo: iStock/SARINYAPINNGAM)
If you’ve had scans done at a polyclinic or public hospital before, your doctor would be able to access those records from the public healthcare system – and reduce duplicating tests and schedule appropriate follow-up scans at the correct time, said Assoc Prof Cheng.
However, “scans done in the private sector or overseas will not be in the clinical notes of the doctor, so it is important for patients to provide such information”, he continued. “The doctor can then take this into account when considering any other medical imaging test.”
WHY DO DOCTORS SOMETIMES ORDER SEVERAL TYPES OF IMAGING TESTS?
Sometimes, “a single scan does not provide sufficient information for an accurate diagnosis”, said Matthew.
“Using multiple imaging modalities allows for a more comprehensive assessment, ensuring precise diagnosis, effective treatment planning, and thorough monitoring of a patient’s condition.”
(Photo: iStock/Wavebreakmedia)
For instance, an X-ray may help doctors detect bone fractures sustained in an accident but it can’t check for internal bleeding and organ damage, which a CT scan and MRI scan can, said Matthew. She cites more scenarios below where multiple imaging tests may be necessary:
- Confirming a diagnosis: Take lung cancer, for example. A chest X-ray may show a lung mass but a CT or MRI scan will provide a clearer view. In stroke patients, a CT scan checks for bleeding in the brain, while an MRI scan assesses the degree of brain damage.
- Monitoring disease progression: Imaging tools such as PET, CT and MRI scans are used to track cancer tumour growths or spread. For patients with chronic illness such as multiple sclerosis, repeated MRI scans are needed to check for new lesions.
- Detecting infection or inflammation: An ultrasound, or CT or PET scan can help to detect infection sources.
SHOULD YOU BE CONCERNED ABOUT DENTAL X-RAYS?
Speak up if you're pregnant. Otherwise, modern X-ray equipment restricts the beam size only to the area that needs to be imaged, said the American Dental Association (ADA), so there isn’t a need for protection such as a thyroid collar against extraneous exposure to radiation.
Following ADA’s guidelines, local dentists such as Dr Andrew Chia from Vista Dental Surgery, also do not use thyroid collars as they “can inadvertently block the X-ray beam, which spoils the image”. “The X-ray will need to be retaken,” he said.
“When this happens, more radiographs need to be taken and unnecessary X-rays are what we want to avoid,” said Professor Purnima Kumar, who chairs the Department of Periodontology and Oral Medicine at the University of Michigan School of Dentistry as well as the ADA Council on Scientific Affairs.
Collapse Expand
HOW ARE THE VARIOUS SCANS DIFFERENT?
Why do you sometimes get a CT scan and not an X-ray? Is the radiation from a mammogram higher than a regular X-ray? We find out:
1. X-RAY
What is it: It uses a form of electromagnetic radiation with high energy to capture detailed images of body structures, said Betty Matthew, a senior principal radiographer from SATA CommHealth. “Since X-rays involve ionising radiation, exposure is carefully controlled and limited.”
Dr Lee Chau Hung, a senior consultant from Tan Tock Seng Hospital’s Department of Diagnostic Radiology, added that X-rays have “a very low radiation dose” and are a “suitable imaging test across all ages and genders”.
When is it used: Typically for detecting fractures, joint dislocations, lung infections such as pneumonia, and certain abdominal conditions, said Matthew.
Who isn’t suitable: Pregnant women as the emissions may harm the development of the foetus. Otherwise, “there are no absolute exclusions for X-ray imaging”, said Matthew. Still, an X-ray is not ordered indiscriminately and “is only recommended when the benefits outweigh the risks”, she said.
2. COMPUTED TOMOGRAPHY (CT SCAN)
What is it: You might associate it with a large, doughnut-like scanner. It emits multiple X-ray beams to produce three-dimensional images of your insides, explained Dr Lee.
When is it used: “It is very useful in providing a detailed visualisation of almost all internal organs.” And with recent technology, you can be scanned from head to toe in just one breath hold or less than 20 seconds, said Dr Lee.
(Photo: iStock/Edwin Tan)
Who isn’t suitable: It requires the highest amount of radiation and is usually avoided in children, pregnant women and young adults, unless absolutely necessary, said Dr Lee.
Also, if you have asthma, allergies or renal impairment, you may not be suitable for a CT scan. A dye or contrasting agent needs to be injected prior to the scan, said Dr Lee, and you may react to the dye.
But it’s not a hard “no” as steroidal medication may help to reduce the risk of an asthma attack or an allergic reaction. Otherwise, an alternative imaging test may be advised for them instead, he said.
3. MAGNETIC RESONANCE IMAGING (MRI)
What is it: This also has a large, ring-like scanner but you'll spend more time in it than the CT scanner. It generates electromagnetic waves to obtain “very detailed three-dimensional images of the internal organs”, according to Dr Lee, and has the "highest resolution among all the imaging tests". But it is also one of the most expensive, he said.
“As no radiation is involved, it is preferred over CT for children and young adults. With recent technology, MRI scans are also safe in pregnancy,” said Dr Lee.
Like CT scans, a dye or contrasting agent is injected to visualise the internal structures more clearly, said Dr Lee. “Newer MRI contrast agents are very safe and can even be used in patients with renal impairment.”
(Photo: iStock/zorazhuang)
When is it used: It is usually reserved for very specific scenarios, said Dr Lee. For example, doctors use it to look for nerve compression in the spine, small tumours in the liver and limbs, or small structures such as the urinary tract and bile ducts.
Who isn’t suitable: Not for patients with claustrophobia or those who can’t keep still and follow certain breathing patterns, said Dr Lee. That’s because it takes a very long time to obtain the images. For example, an MRI scan of the lower back takes about 15 to 20 minutes, he said, while the liver can take up to 30 minutes.
“Most importantly, because MRI requires the use of high-intensity magnetic waves, it may not be safe for patients with metal implants such as clips, staples, heart stents or metallic foreign objects as they may get heated or even move within the body,” he clarified.
3. ULTRASOUND
What is it: You would have watched enough TV to associate ultrasound imaging or sonography with babies in the womb. And for good reason: “It is a safe and widely used diagnostic tool that does not involve radiation,” said Matthew.
“Instead, it uses high-frequency sound waves to create real-time images of internal organs and blood vessels,” she said. To obtain the images, a gel is applied and a small device is placed on the area of interest such as the abdomen or back to take pictures of the various organs underneath.
(Photo: iStock/Pitchayanan Kongkaew)
When is it used: Ultrasound is commonly used in obstetrics and gynaecology to monitor foetal development as well as for assessing various medical conditions, according to Matthew.
“It is ideal for soft tissue evaluation, including monitoring pregnancy, assessing abdominal organs, detecting gallstones, and examining blood flow in blood vessels. It is also used for guided procedures such as biopsies,” she said.
Who isn’t suitable: Ultrasound can’t penetrate bone and won’t be able to show what lies within, according to Singhealth.
It also cannot pass through air such as intestinal gas, so an evaluation of the stomach, small intestine and large intestine may be limited. Deeper body parts such as the pancreas and aorta may also be limited, especially if the patient is obese, because body tissue weakens the sound waves the deeper they pass into the body.
4. MAMMOGRAM
What is it: Put simply, it is a specialised X-ray of the breasts. “It can identify abnormalities in the breast before symptoms appear, significantly improving treatment outcomes,” said Matthew.
The scan itself is actually very fast, typically a few seconds, according to Dr Lee. “However, time is needed to position the breast to obtain the best images and this may take an additional 5 to 10 minutes, depending on how many extra images are needed.”
“Also, as compression on the breast tissue is needed,” he highlighted, “it can be a little bit uncomfortable for the patient.”
(Photo: iStock/andresr)
When is it used: Other than regular screening, “mammograms are also used for individuals experiencing symptoms such as lumps or breast pain to detect any abnormalities”, said Matthew.
Who isn’t suitable: Because radiation is used, this test is avoided in young women until they reach the recommended age for screening, said Dr Lee.
5. BONE DENSITY SCAN
What is it: “This is a very special type of scan that uses X-rays to determine bone strength,” said Dr Lee. The hip or wrist is usually scanned and it takes just a few minutes to position the body part and perform the scan, he said.
When is it used: “This test is usually performed for elderly patients who are more prone to osteoporosis. However, young patients may be required to undergo this test if they are on certain medications that may affect bone density," said Dr Lee.
Who isn’t suitable: Pregnant women as radiation is involved. Those who have undergone recent major spinal surgeries and individuals with severe spinal abnormalities such as scoliosis are also excluded as the results might be inaccurate.
(Photo: iStock/Mindful Media)
6. POSITRON EMISSION TOMOGRAPHY (PET SCAN)
What is it: This is a highly specialised scan of the whole body, according to Dr Lee. “A special radioactive dye is injected and the patient lies in a scanner, which detects the dye as it is absorbed by different organs.”
He highlighted that the process takes about two to three hours in total because the dye takes time to be absorbed by the different organs before the scan is performed.
When is it used: The main use of this scan is for the detection of cancer and cancer spread, but it can also be used to look for a source of infection, said Dr Lee.
Who isn’t suitable: This scan is usually avoided in children and pregnant patients as there is radiation involved, said Dr Lee.
Continue reading...