18-20 Week Screening Pregnancy Ultrasound
What are the generally accepted indications for 18-20 week screening pregnancy ultrasound? Ultrasound at 18–20 weeks of gestation has become…Read more
Ideally MRI should be scheduled for days 6-12 of the menstrual cycle unless there is a clinical urgency to have the procedure performed as soon as possible (e.g. known breast cancer awaiting treatment).
Ideally, breast MRI should not be performed in women who are taking hormone replacement therapy (HRT) as this may cause hormonal related parenchymal contrast enhancement which can obscure pathological changes and make study interpretation difficult. If the indication for the study is not urgent, then cessation of HRT for 4-6 weeks prior to the study is suggested.
MRI is best avoided during pregnancy unless the clinical indications outweigh the small (currently unknown) risks involved. If there is a possibility the patient could be pregnant then a pregnancy test is suggested prior to the scan, or alternatively the procedure could be rescheduled until after the next menstrual period starts.
MRI can be performed on lactating women, however image interpretation may be more difficult due to the hormonal stimulation of the breast.
Excretion of gadolinium contrast agent into breast milk has been shown to be minimal (0.01%) and very little (less than 1%) of the drug is absorbed by the baby when taken in this way which is far less than the dose of gadolinium given to a baby having an MRI. If the patient is breastfeeding it is quite safe to continue this after the examination as studies have shown that only a very tiny amount of the contrast material is absorbed by the baby from the milk.
Claustrophobia: 1-4% of women suffer from claustrophobia and some will not be able to tolerate being in the MRI machine. Some of these women may be able to tolerate the examination if they are given anxiolytic premedication. Please discuss this issue with your patient and the personnel at the MRI facility at the time of booking the procedure.
A safety screening questionnaire should be completed by every patient prior to MRI. This asks questions regarding the presence of ferromagnetic objects, implants and pacemakers and is designed to ensure that no contraindications are present to exposure of the patient to high magnetic fields.
Patients with impaired renal function are at risk of developing Nephrogenic Systemic Sclerosis.
Biochemical screening for impaired renal function is not thought to be warranted in the absence of relevant history or symptoms. If there is any reason to suspect the presence of renal impairment, estimation of GFR should be performed prior to gadolinium administration.
Patients with known allergy to gadolinium contrast agents should not undergo contrast enhanced breast MRI. Breast MRI to detect presence of breast implant complications does not require injection of contrast and can be safely performed in this setting.
Patients with ferrous aneurysm clips, known metallic foreign bodies in the eye, bionic ear implants, cardiac pacemakers, vascular filters (AAA-Zenith stent) and tissue expanders should not have MRI.
Patients with severely impaired renal function (GFR<30ml/min/1.73m2) should not have a breast MRI examination with IV contrast due risk of developing NSF (nephrogenic systemic sclerosis).
Patients with a history of allergy to iodinated contrast, other allergies and a history of asthma are at increased risk of an adverse reaction to gadolinium.
Patients with mild-moderate renal impairment (eGFR between 30 and 60 ml/min/1.73m2) should not undergo contrast enhanced breast MRI unless the benefits of having the test are considered to outweigh the risk of developing NSF. If contrast injection is needed, a reduced dose of a cyclic form of gadolinium contrast agent, pre-hydration and written informed consent from the patient should be obtained.
Patient pregnancy. There is not enough evidence to determine whether MRI is without risk during pregnancy. Whilst there are no known adverse effects, the consequences of foetal exposure to strong magnetic fields are uncertain. The intravenous contrast agent (which contains gadolinium DTPA) does cross the placenta and the long term effects on the foetus are uncertain. The hormonal effects of pregnancy may cause extensive background glandular contrast enhancement, reducing the sensitivity of breast MRI in detecting abnormalities. Breast MRI should be delayed until after delivery of the baby unless there are exceptional circumstances where the information provided by the MRI is worth the very small potential, but unproven, risk to the foetus.
Patient size. Obese patients who weigh more than the maximum weight limits for the sliding table may not fit into the magnet.
The total incidence of adverse reactions to MRI contrast agents is approximately 2-4%.
The most common reactions are headaches, dizziness, nausea and emesis. Local injection site symptoms such as pain, warmth, or burning sensation and localised oedema may occur. Other adverse events include chest pain/tightness, fever, fatigue, arthralgias, rigors, asthenia, hot flashes, malaise, weakness, facial oedema, neck rigidity, abdominal cramps, itching, watery eyes, tingling sensation in the throat.
Moderate to major adverse reactions including airway compromise and circulatory collapse have been reported in approximately 1 in 10,000 studies.
Nephrogenic Sclerosing Fibrosis is a rare multi-systemic fibrosing disorder that principally affects the skin but may also affect other organs of patients with renal insufficiency.
See Gadolinium Contrast Medium (MRI Contrast agents) for more information.
The acoustic noise produced during MRI can be distressing for patients and can result in reversible hearing loss if the patient does not wear ear protection (disposable ear plugs or headphones are supplied to prevent this).
Breast MRI is an expensive test with limited availability. It is best used for specific clinical indications in conjunction with routine breast imaging studies such as mammography and ultrasound.
It is vital that the referral contains all the relevant clinical information regarding previous history, pathology results and imaging procedures. It is vital that the patient brings all her previous breast imaging studies in to the MRI unit when she has her study performed so that the reporting radiologist can produce the most clinically relevant and accurate report possible.
MRI is very sensitive but relatively non-specific, resulting in a significant number of false positive findings. The findings on MRI may require further investigation with ultrasound and biopsy to determine their significance. Indeterminate or suspicious lesions seen on ultrasound can be biopsied using US guidance but about 20-30% of lesions may not be visible on ultrasound and will require either MRI guided biopsy or MRI guided hookwire localisation and surgical biopsy to rule out malignancy. Many of these potential abnormalities shown on MRI will be benign and the process of investigating these may cause significant patient anxiety, inconvenience and expense.
MRI should not supplant careful problem-solving mammographic views or ultrasound in the diagnostic setting. Because MRI will miss some cancers that mammography will detect, it should not be used as a substitute for screening mammograms. MRI should not be used in lieu of biopsy of a mammographically, clinically, and/or sonographically suspicious finding.
Breast ultrasound is the imaging modality of choice in the pregnant patient.
Page last modified on 26/7/2017.
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