Body Imaging
Cancer Screening and Preventative Medicine
Why Consider Body Imaging?
Traditional annual examinations are limited by a lack of imaging modalities. Sometimes an ultrasound is done for the abdomen which is limited by the depth of penetration, often missing things like the pancreatic tail, and missing structures due to bowel gas.
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"The traditional annual physical examination of asymptomatic adults is not supported by evidence of effectiveness" (Canadian Task Force on Preventative Healthcare 2017)
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Body Imaging however, at minimum, is an alternative method of physical examination by visualizing soft tissues, and create a way of cataloging various organ structures and variants (such as cysts).
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As a Screening Test, Body Imaging offers insight into any suspicious solid masses, which can be followed with diagnostic tests specific to that mass (thyroid ultrasound for thyroid nodules, CT adrenal protocol for adrenal nodules)
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Body Imaging also offers a retrospective comparison when done tandemly, to monitor masses and nodules changing or enlarging over time. This will provide guidance on whether to follow something closely with diagnostic scans.
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MRIs do not emit ionizing radiation, and thus scans are not damaging to the body.
There is meta-analysis evidence showing whole-body MRI has similar diagnostic performance as PET/CT scans without the radiation. PMID: 24355655
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Non-Cancer Pathology
Cancer prevalence is low. However, Body Imaging can pick up other pathology which can be useful to your doctor to improve Preventative Healthcare.
For example:
1) White-matter changes in the brain is indicative of chronic small vessel disease and a risk factor for Stroke and Dementia. This may lead your doctor to use GLP-1 agonist medications if you have diabetes, which has a 17% benefit for stroke prevention.
2) Fatty infiltration of the liver may lead to the use of omega-3 supplements, Mediterranean Diet, and motivate patients for Weight Loss.
3) Thickened bladder wall may be a sign of chronic bladder outlet obstruction/urinary retention and lead to investigations and medications to improve urine flow and prevent UTIs.
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Incidental findings, commonly coined as "incidental-omas" are often variants of normal structures, or inconsequential pathologies, such as hemangiomas of the liver, simple cysts of the kidneys and of the reproductive tract. If these do not produce outright concern in the patient's health context, then they are simply monitored year-on-year on the next MRI.
Year-on-year interval stability is reassuring for a benign nature.
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Cancer Screening
Cancers grow at different rates. They usually start slow, and increase in growth rate with time as they accumulate more mutations. There are some data from Surveillance Epidemiology and End Results (SEER) registries that estimate the time that it takes from cancer formation to clinical manifestation with symptoms.
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For example:
1) Pancreatic Cancer: 1.7 years (females) 3.0 years (males)
2) Colon Cancer: 6.5 years (females), 5.4 years (males)
3) Gastric Cancer: 10.6 years (females) 9.5 years (males)
4) Lung Neuroendocrine Tumor: 5.5 years (females), 2.5 years (males)
PMID: 23054397, PMID: 24915123
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When it comes to screening, we take the lowest common denominator: pancreatic cancer (adenocarcinoma) 1.7 years (females), and sample (do MRIs) at double the frequency according to Nyquist Sampling Theorem. This suggests scanning every 0.85years to be able to capture pancreatic adenocarcinomas (which is the the more aggressive version).
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For practical purposes, we suggest a scan every 12months.
Body Imaging combined with Multi-cancer Early Detection tests can increase probability of identifying possible cancers,
and are already recommended for patients with hereditary cancers. PMID: 32345712, PMID 28772291
As of early 2024 there is already starting to be literature validating the ONCO-RADS criteria to whole-body MRIs in an effort to streamline classification and communication between physicians. PMID 38326850
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Limitations
MRIs are better at looking at soft tissues than CT scans, but are limited by noise signals from movement. Hence it does not have good resolution for the middle of the lung (lung parenchyma), and results can be compromised by frequent body movement in the MRI. CT low-dose of the chest can be considered for high risk patients with significant smoking history, in accordance with the Canadian Task Force on Preventative Healthcare 2016 Guidelines.
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One method of overcoming this problem is to overlap MRIs with Multi-cancer Early Detection (McED) tests, and only order Diagnostic CT chest if there is positive signal for lung cancer on McED.
