3D mammograms and contrasted mammograms: what are they, and why do general practitioners need to know about them? Although you may not encounter these imaging techniques often in your daily practice, you may occasionally have patients asking about them, particularly given our increasingly health-conscious population.
Patients participating in the national breast cancer
screening programme who have abnormal findings on
initial screening mammograms will often be recalled
for further assessment, which entails usage of newer
techniques such as 3D mammograms and contrasted
mammograms.
This article provides an overview of
their indications, utility and limitations.
1. DIGITAL BREAST TOMOSYNTHESIS
WHAT IS DIGITAL BREAST TOMOSYNTHESIS?
Digital breast tomosynthesis (DBT), also known as 3D
mammogram, is a type of mammography that uses
X-rays to produce detailed three-dimensional images
of the breast tissue.
How does it work?
It involves multiple projections acquired across an
arc that are reconstructed into a series of stacked
images. The tomosynthesis data set can then be used
to recreate two-dimensional images using synthetic
mammography (SM), producing images almost
equivalent to those of the traditional full-field digital
mammography (FFDM).1
Hence, in a DBT study, you will get a series of stacked
images of each breast in two views and a set of
synthesised mammogram which is almost of traditional
mammogram equivalence.
WHEN AND WHY DO WE USE DBT?
The stacked images from DBT facilitate visualisation,
localisation and characterisation of a lesion.
Further assessment of asymmetric density on
screening mammogram
Some patients may be recalled for assessment of
asymmetric density present on the screening mammogram.
The multiple sections and additional angles
available with DBT imaging often allow the resolution
of areas of normal superimposed tissue that may
present as summations or higher density areas in
FFDM.
If the supplementary ultrasound also did not reveal
any significant abnormalities, patients can usually be
discharged back to routine rescreening without further
investigation or biopsy.
Detecting mammographic architectural distortion
The beauty of DBT lies in its ability to comprehensively
assess mammographic architectural distortion, the
most common missed abnormality in interval cancers. It has also been shown to improve the detection of
such distortion.
Figure 1A shows an example of a patient with extremely dense breasts, who was recalled for assessment
of possible architectural distortion in the right breast. The area of distortion was incredibly subtle on the screening mammogram. In fact, it was missed by one
reader, but was depicted clearly on DBT.
Supplementary ultrasound examination showed a
corresponding irregular hypoechoic lesion which
was suspicious in nature, and was biopsied under
ultrasound guidance (Figure 1B). Histology yielded
invasive ductal carcinoma with lobular differentiation.
Lower recall rates and increased cancer
detection rates
Some countries with historically high breast cancer
screening recall rates have managed to significantly
lower their recall rates and improve specificity
after replacing FFDM with DBT imaging as a first-line
screening tool (FFDM remains as the first-line screening
tool in Singapore).
Prospective and retrospective observational studies
have reported a 15% to 63% decrease in recall rate.1-5
Other studies have demonstrated an increase in
cancer detection rate (CDR) after employing DBT as a screening tool. In particular, there was a higher
pick-up rate of both smaller as well as lower-grade
malignancies.1-3
That said, its long-term impact on patient survival
remains uncertain as breast cancer survival benefits
are difficult to prove without extended follow-up and/
or randomised controlled trials.
DBT use in Singapore
DBT is not currently used as a screening tool in
Singapore. It is associated with longer acquisition and
interpretation times owing to the larger image set.
There is also a slight increase in radiation dose with
DBT relative to FFDM.
Currently, it serves as an adjunct problem-solving
imaging tool in the hospital setting to assess
abnormal breast findings and assist in lesion-localisation
for biopsy.
Ongoing research to reduce DBT reading time and
improve its imaging performance may change the
status quo.1
HOW MUCH MORE RADIATION DOES
DBT HAVE COMPARED TO A NORMAL
MAMMOGRAM? In a review by Svahn et al., the authors concluded
that while using DBT plus FFDM increases
radiation dose by a factor of up to 2.25 compared
with FFDM alone, using SM to replace the FFDM
portion can bring the radiation dose to a level
comparable to that of FFDM alone.4
According to Skaane et al., the dose with DBT
plus SM is reported to be just 19% higher than
that with FFDM alone. The use of SM in place of
FFDM with DBT pro-vides similar outcomes while
reducing radiation dose.5
In summary, modern-day DBT imaging has a
similar or just slightly higher radiation dose as
compared to a normal mammogram. I HAVE HEARD ABOUT THIS ‘SPECIAL
MAMMOGRAM’. AM I ABLE TO GO
FOR IT? DBT is only indicated in certain specific cases,
which first requires an initial evaluation by a
breast surgeon or radiologist. This facility is
only available in hospitals and not in government
polyclinics. |
2. CONTRAST-ENHANCED SPECTRAL MAMMOGRAM
WHAT IS A CONTRAST-ENHANCED SPECTRAL
MAMMOGRAM?
Contrast-enhanced spectral mammogram (CESM) provides additional information beyond a conventional
mammogram and may aid earlier detection of
some cancers. It is a recent development in digital
mammography that utilises dual-energy exposure
following the injection of an iodinated contrast
agent.5-6
How does it work?
Typically, an iodinated contrast agent (1.5 ml/kg of
body weight) will be administered to the patient via
intravenous injection. Two minutes later, standard
mediolateral oblique (MLO) and craniocaudal (CC)
projections will be undertaken on each breast.
Each projection will receive two exposures, one with
a low energy (around 30 kVp) and the other with a
high energy (around 45 kVp). A specific dual-energy
image recombination algorithm is used to subtract the
low- and high-energy images, resulting in an ‘iodine uptake map’.
Hence, there will be two sets of images in a CESM
study:
A set of low-energy images, which looks like a conventional mammogram
A set of recombined images, which displays contrast medium uptake
The entire process usually takes about 30 minutes.6-7
CESM, likened to MRI breasts, leverages on tumoural
neoangiogenesis.8,9 It provides both morphological
information, similar to a routine mammogram, and
functional information about a lesion’s enhancement
pattern. Several studies have demonstrated the
superior sensitivity and low false positive rates
of CESM, with studies exploring its potential as an alternative to MRI breasts in breast cancer staging and
problem solving.6-8
CESM use in Singapore
This imaging technique has been available in Singapore for the last five to eight years. We have found it
relatively easy to adopt in a hospital setting, and it has
been helpful in our clinical practice.
WHEN AND WHY DO WE USE CESM?
Indications
CESM is indicated:
- For the evaluation of an ultrasound-occult
asymmetric density
- For delineation of tumour extent
- As a problem-solving tool in complicated cases
Contraindications
Contraindications for CESM are identical to contrast-enhanced
CT scans, which include:
- Renal impairment
- Contrast allergy
- Asthma
- Pregnancy (due to radiation) – the radiation dose
of CESM relative to mammogram reportedly
ranges from 1.06 to 1.437
Improving diagnostic accuracy and care
The addition of CESM to our workflow has helped
improve diagnostic accuracy and patient care. As
an example, the initial assessment of a patient with
abnormal findings in the left breast showed a suspicious
mass and an indeterminate left axillary lymph
node. They were biopsied under ultrasound guidance
and proven to be invasive breast cancer and metastatic
left axillary adenopathy respectively (Figure 2A).
The addition of CESM into the workflow enabled the
detection of an additional enhancing lesion in the right
breast (Figure 2B) which was not visible on routine
mammogram and ultrasound. This enhancing lesion
in the right breast, detected only on CESM, was also
subsequently proven to be invasive breast cancer.
According to reports, the false positive rate of CESM is
comparable to or even lower than that of MRI breasts.9 There is ongoing research into CESM screening and
CESM-guided biopsy, with this imaging technique
having generated a fair bit of excitement among the
breast imaging community.
WILL THERE BE AN ALLERGIC REACTION
RELATED TO CONTRAST ADMINISTRATION
IN CESM? HOW IS IT MANAGED? Administration of an iodinated contrast agent is
essential to the examination and, like any other
contrast-enhanced CT examination, carries a
small risk of allergic reactions. These occur
in less than 1% of cases and are typically mild
and self-limiting. In one of the largest studies, out of 839 women
who underwent CESM, there were only five with
minor reactions (0.6%). Four of these resolved
without any medical intervention, and one patient
experienced urticaria and breathlessness
and was treated with intravenous corticosteroids
with complete resolution of symptoms.10 Late reactions are usually self-limiting and
require no specific therapy except for symptomatic
treatments such as antihistamines and
corticosteroids.10 If symptoms persist or worsen,
a referral to an allergic specialist for further
management should be considered. Please refer to local guidelines for the management
of contrast reactions.
WILL THERE BE CONTRAST-INDUCED
NEPHROPATHY RELATED TO CONTRAST
ADMINISTRATION IN CESM?
The incidence of contrast-induced nephropathy (CIN) has been reported to range from 0% to 24%. This wide range is attributed to differences in definition, background risk factors, type and dosage of the contrast medium used.12 In a recent nationwide audit in the United Kingdom, no cases of post-contrast acute kidney injury were identified in 3,590 outpatients.6,13 CIN is usually transient and reversible, and tends to improve within three to seven days.6, 11-12 Patient eligibility for contrast administration is carefully considered. In a fit outpatient without any history of renal disease or other risk factors (e.g., advanced age or diabetes), there is likely to be a negligible risk of acute kidney injury with the administration of a contrast agent.6 We also typically advise our patients to maintain adequate oral hydration following the examination, as this is an important preventive measure for CIN.11-12
|
CONCLUSION
DBT and CESM are relatively new breast imaging
techniques that have recently cemented their places
in clinical practice. They are practical tools that we
use in the hospital setting, and a brief understanding
of them may help in communication with your patients
and for continuity of care.
REFERENCES
Chong A, Weinstein SP, McDonald ES, Conant EF. Digital Breast Tomosynthesis: Concepts and Clinical Practice. Radiology. 2019;292(1):1-14.doi:10.1148/radiol.2019180760
Conant EF, Beaber EF, Sprague BL, et al. Breast cancer screening using tomosynthesis in combination with digital mammography compared to
digital mammography alone: a cohort study within the PROSPR consortium. Breast Cancer Res Treat. 2016;156(1):109-116. doi:10.1007/s10549-016-3695-1
Sharpe RE, Venkataraman S, Phillips J, et al. Increased Cancer Detection Rate and Variations in the Recall Rate Resulting from Implementation
of 3D Digital Breast Tomosynthesis into aPopulation-based Screening Program. Radiology. 2016;278(3):698-706. doi:10.1148/radiol.2015142036
Svahn TM, Houssami N, Sechopoulos I, Mattsson S. Review of radiation dose estimates in digital breast tomosynthesis relative to those in two-view
full-field digital mammography. The Breast. 2015;24(2):93-99. doi:10.1016/j.breast.2014.12.002
Skaane P, Bandos AI, Gullien R, et al. Prospective trial comparing full-field digital mammography (FFDM) versus combined FFDM and tomosynthesis
in a population-based screening programme using independent double reading with arbitration. Eur Radiol. 2013;23(8):2061-2071. doi:10.1007/s00330-013-2820-3
James JJ, Tennant SL. Contrast-enhanced spectral mammography (CESM). Clinical Radiology. 2018;73(8):715-723. doi:10.1016/j.crad.2018.05.005
Dromain C, Vietti-Violi N, Meuwly JY. Angiomammography: A review of current evidences. Diagnostic and Interventional Imaging. 2019;100(10):593-605. doi:https://doi.org/10.1016/j.diii.2019.01.011
Tagliafico AS, Bignotti B, Rossi F, et al. Diagnostic performance of contrast-enhanced spectral mammography: Systematic review and meta-analysis. The Breast. 2016;28:13–19
Elżbieta Łuczyńska, Sylwia Heinze-Paluchowska, Edward Hendrick, et al. Comparison between Breast MRI and Contrast-Enhanced Spectral Mammography. Medical Science Monitor. 2015;21:1358-1367. doi:10.12659/MSM.893018
Houben IPL, Van de Voorde P, Jeukens CRLPN, et al. Contrast-enhanced spectral mammography as work-up tool in patients recalled from breast cancer screening has low risks and might hold clinical benefits. European Journal of Radiology. 2017;94:31-37. doi:10.1016/j.ejrad.2017.07.004
Modi K, Padala SA, Gupta M. Contrast-Induced Nephropathy. In: StatPearls. StatPearls Publishing; 2022. Accessed February 1, 2023. http://www.ncbi.nlm.nih.gov/books/NBK448066/
Hossain MA, Costanzo E, Cosentino J, et al. Contrast-induced nephropathy: Pathophysiology, risk factors, and prevention. Saudi Journal of Kidney Diseases and Transplantation. 2018;29(1):1. doi:10.4103/1319-2442.225199
Cope LH, Drinkwater KJ, Howlett DC. RCR audit of compliance with UK guidelines for the prevention and detection of acute kidney injury in adult patients undergoing iodinated contrast media injections for CT. Clinical Radiology. 2017;72(12):1047-1052. doi:10.1016/j.crad.2017.07.002
Dr Amanda Liew graduated from the University of Edinburgh with honours in 2014 and became a Fellow of the Royal College of Radiologists in 2018. She attained her specialist accreditation in diagnostic radiology in 2021. She is currently an Associate Consultant at the National Cancer Centre Singapore, and her special interests are in breast imaging, breast cancer research and education.
GPs can call the SingHealth Duke-NUS Breast Centre for appointments at the following hotlines or click here to visit the website:
Singapore General Hospital: 6326 6060
Changi General Hospital: 6788 3003
Sengkang General Hospital: 6930 6000
KK Women’s and Children’s Hospital: 6692 2984
National Cancer Centre Singapore: 6436 8288
