#61 - Rajpaul Attariwala, M.D., Ph.D.: Cancer screening with full-body MRI scans and a seminar on the field of radiology
Dr. Raj Attariwala, a radiologist/engineer, discusses his unique MRI technology for high-resolution whole-body imaging and its implications for early cancer detection. He and Peter explore various imaging modalities, their physics, uses, and risks like radiation and false positives.
Deep Dive Analysis
14 Topic Outline
Raj Attariwala's Background: Engineering to Radiology
Understanding X-rays: Mechanics, Radiation, and Risks
Computed Tomography (CT) Scans: 3D Imaging and Contrast
Ultrasound: High-Frequency Sound Waves and Limitations
Mammography: Breast Density, Sensitivity, and Specificity
Magnetic Resonance Imaging (MRI): Physics and Fundamentals
Brain Aneurysms: Detection and Clinical Significance
Raj's Unique MRI Technology: Hardware and Optimization
Diffusion-Weighted Imaging (DWI): Functional MRI for Cancer Detection
False Positives and Cancer Screening with DWIBS MRI
Comparing DWIBS MRI to PET-CT for Whole-Body Screening
Prostate Cancer Screening: MRI with DWI and Blood Tests
Standardization Challenges in MRI Technology
Future of MRI: Speed, Resolution, and Machine Learning
8 Key Concepts
Millisievert
A unit of measurement for radiation exposure, set by the System Internationale, used to quantify the amount of energy deposited in the body from ionizing radiation.
Sensitivity
In medical testing, sensitivity refers to the true positive rate. If 100 people have a disease, and a test has 80% sensitivity, it will correctly identify 80 of them as positive, missing 20 (false negatives).
Specificity
In medical testing, specificity refers to the true negative rate. If 100 people do not have a disease, and a test has 90% specificity, it will correctly identify 90 of them as negative, while 10 will be false positives.
Hounsfield Units
A calibrated scale used in CT scans to measure tissue density, ranging from -1000 (air) to 0 (water) to 2000 (dense bone), allowing differentiation of various body tissues.
T1-weighted MRI
An MRI sequence that highlights fat, making it appear bright, and provides excellent anatomical detail, closely resembling what one expects to see.
T2-weighted MRI
An MRI sequence that highlights both fat and water, making water appear bright. It is particularly useful for detecting edema (swelling) and takes longer to acquire due to longer echo times.
DWI/DWIBS
Diffusion-Weighted Imaging (DWI) or Diffusion-Weighted Imaging with Background Subtraction (DWIBS) is a functional MRI technique that detects restricted water movement within tissues. This restriction indicates areas of high cellular density, often associated with tumors or 'lumps'.
Isotropic Imaging
A method of imaging where data is acquired in perfect cubes (e.g., 1x1x1 millimeter). This allows for viewing the image in any three-dimensional direction without loss of resolution or distortion.
10 Questions Answered
An X-ray works by passing high-energy wavelengths through the body. Dense materials like bone block the X-rays, appearing white on film, while soft tissues and air allow them to pass through, appearing black.
Ionizing radiation from X-rays and CT scans can damage cells and DNA, increasing the risk of inducing cancers. The risk is higher for younger individuals and females, with the highest risk for females around age 12.
A CT scan is like a powerful X-ray that spins around the body, taking multiple images from different angles to create a three-dimensional view, offering much more detailed anatomical information than a single 2D X-ray.
Ultrasound uses high-frequency sound waves that reflect off tissue interfaces, similar to an echo, to create an image. Its limitations include poor penetration through air (like in the lungs or bowel) and lower resolution compared to other modalities, requiring significant operator skill.
Mammograms are very effective at seeing through fatty breast tissue, but dense glandular tissue can obscure potential cancers, significantly reducing the mammogram's sensitivity. Women with dense breasts may require additional imaging like ultrasound or MRI.
An MRI uses a strong magnetic field to align the hydrogen nuclei (protons) in the body's water and fat molecules. Radiofrequency pulses then temporarily disrupt this alignment, and as the protons relax back, they emit signals that are detected and converted into detailed images.
A 1.5 Tesla magnet has a longer electromagnetic wavelength (around 30 cm) compared to a 3 Tesla magnet (around 15 cm), which allows for greater penetration and more uniform imaging across the entire body, especially when the hardware and software are meticulously optimized for signal-to-noise ratio.
DWI detects areas where water movement is restricted, indicating high cellular density, which is characteristic of tumors. This functional information, combined with anatomical MRI, provides a powerful 'lump detector' for early cancer detection without radiation.
PET-CT scans using radioactive glucose (FDG) are less effective for imaging the brain (due to high normal glucose uptake), kidneys, and bladder (due to glucose excretion), and the prostate (due to poor perfusion), potentially missing cancers in these areas.
Standardization is critical because MRI results can vary widely between machines and sites due to different tuning parameters, making it difficult to compare scans or ensure consistent image quality. Currently, there is a lack of universal standardization, leading to inconsistent results.
25 Actionable Insights
1. Minimize CT Scans for Young Females
Be aware that younger individuals, especially females, have a greater risk of cancer induction from CT scans, so minimize exposure, particularly in pediatric cases.
2. Electively Screen for Brain Aneurysms
Consider screening for brain aneurysms using MRI, as early detection allows for elective treatment options like coiling or clipping, significantly reducing the high mortality risk associated with rupture.
3. Screen for Aneurysms with Family History
If there is a family history of aneurysms, especially at a young age, consider MRA (magnetic resonance angiography) screening due to a potential genetic component, even if insurance initially declines coverage.
4. Personalize Cancer Screening Decisions
Understand that cancer screening is a very personal decision with risks, particularly false positives leading to emotional distress and potential harm, so approach it thoughtfully.
5. Combine Mammogram and DWI MRI
For comprehensive breast cancer screening, combine mammography (to detect calcifications) with a high-quality diffusion-weighted imaging (DWI) MRI, as this combination is highly sensitive and unlikely to miss cancer.
6. Consider Additional Imaging for Dense Breasts
If you have dense breast tissue, a mammogram might not be sufficient, so consider additional imaging modalities like ultrasound or MRI to effectively screen through the glandular tissue.
7. Know Your Breast Density
Understand your breast density, as mammogram sensitivity is significantly lower (around 55%) for dense breast tissue compared to fatty tissue (over 95%), impacting the test’s effectiveness.
8. Check Mammogram for Density
Always check your mammogram report for information on breast tissue density, as this detail helps you understand if the mammogram alone is sufficient for effective screening.
9. Get Regular Mammograms
Get mammograms at regular intervals (one or two years) because comparing images over time is far more sensitive for detecting subtle changes than evaluating a single mammogram.
10. Early Breast Screening for Family History
If you are under 40 and have a family history of early-age breast cancer, consider discussing screening options, as standard mammography guidelines often exclude this age group.
11. Consider Prostate MRI Screening
Explore MRI with diffusion-weighted imaging (DWI) for prostate cancer screening, as it is becoming a de facto standard in some countries for better differentiation of aggressive versus indolent cancers.
12. Be Cautious About MRI Quality
Be aware that MRI quality and standardization vary significantly between clinics and machines, unlike CT scans, so research and choose your MRI provider carefully.
13. Know Imaging Radiation Exposure
Understand that different imaging technologies, like X-rays or mammograms, expose you to varying amounts of radiation, generally increasing from simple X-rays to whole-body PET-CTs.
14. Calculate Personal Radiation Dose
Use an online calculator to determine your personal radiation dose from various exposures, including medical imaging and travel, as this is a requirement for professions like pilots.
15. Seek Clear Imaging Answers
When undergoing imaging, aim for technologies that provide clear ‘yes or no’ answers regarding potential problems, such as combining functional and anatomic imaging for definitive diagnoses.
16. Embrace AI for Longitudinal Imaging
For repeat scans, machine learning can significantly improve efficiency by performing ‘subtraction’ analysis to highlight subtle differences over time, helping to detect changes more easily.
17. Utilize AI for Imaging Review
Be open to the future integration of machine learning and AI as a ‘second reader’ for imaging, which aims to improve radiologist efficiency and reduce missed diagnoses, similar to its current use in mammography.
18. Understand Medical Imaging
Listen to this technical episode if you’ve ever had an X-ray, CT scan, ultrasound, or MRI, as it provides crucial understanding of these technologies that most doctors don’t fully grasp.
19. Utilize Show Notes for Visuals
Refer to the show notes for this episode, as they will pair discussions with images to help visualize and understand complex radiology concepts, especially MRI.
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5 Key Quotes
The famous equation is that one plus one equals three. These two separate modalities of functional imaging and anatomic imaging come together to actually make something better than each part individually.
Raj Attariwala
The younger you are, the greater the risk of cancer induction from CT scanners, which is why in the pediatric world, we actually try and really minimize the amount of dose that children in particular are getting.
Raj Attariwala
You can make a test that is a hundred percent sensitive, if you're willing to have zero percent specificity and vice versa.
Peter Attia
It's not always bigger. It's kind of like, if you really understand what you're doing and want to get underneath the hood, you can take that 1.5 liter engine, you can put the turbochargers on it. You can put, you know, like the multiple valves and the everything to actually get the torque and horsepower you want out of it. But most people don't think that way. They think bigger is better.
Raj Attariwala
The mortality of a ruptured aneurysm is over 93 to 95%. So most people don't make it. Whereas when you do find them earlier, there's all sorts of options, such as coiling, where you can actually treat it or clipping.
Raj Attariwala