BMEN 311 - Exam 2

Contains Lecture content from X-rays all the way to MRI

What are the Advantages with MRI imaging?

• it is great at soft tissue contrast

• it is great to get a detailed image of anatomical aspects

• it pairs well with functional aspects like PET scans

what are the disadvantageous with MRI?

• terrible for metal implants

• patients needs to be motionless for a long time

• RF signals have a potential to heat up the patient

• they are expensive and imaging takes a while

what is the lamor frequency?

this is the frequency that the RF coils are tuned to to induce rotation of the hydrogen atoms.

how does contract occur in MRI images?

tissues release different amounts of energy when the hydrogen atoms are return to alignment

what happens if we increase the magnetic field of the MRI machine?

It results in higher resolution

what is T1 Relaxation?

Used in Fatty tissue while suppression of the signal of water. This measures how quickly the hydrogen atoms align with the magnetic field

what is T2 Relaxation?

This is uses to enhance signals from water. it keep tracks of how quickly the hydrogen atoms points perpendicular to the magnetic field lose their linearity.

what kind of wave does US use?

A mechanical-longitudinal wave: it requires a medium (gel / tissue) and its particles oscillate back-and-forth along the beam axis. Thus “mechanical” describes the need for a medium; “longitudinal” describes the particle motion.How the piezoelectric effect runs an ultrasound transducer

How the piezoelectric effect runs an ultrasound transducer

1. Transmit – Reverse effect: the pulser sends an alternating voltage; piezo-electric crystal oscillates at MHz rate → launches a mechanical-longitudinal sound pulse into the patient.
2. Receive – Direct effect: returning echo compresses the crystal; that mechanical stress produces a proportional voltage signal.
3. Electronics measure echo time (depth) & amplitude (brightness) to render the B-mode image.

What are higher frequency US transducers used for?

Superficial Structures like vascular and peripheral nerves

What are lower frequency US transmitters used for?

Deeper Structures such as throax, abdomen and pelvis.

What is Axial resolution in US?

it is the shortest distance of two distiguisable structures parallel to the beam. It dependent on frequencywhat

what is lateral resolution in US?

is is given by the shortest distance of two structures perpendicular to the beam. it is dependent on beam width.

what is acoustic impedance?

the resistance to propagation of soundwaves through tissues

What does Refraction do to a tissue on a US image?

when two adjacent tissues have lightly different impedance values. They will appear similar gray levels.

what does Reflection do to a US image?

two adjacent tissues have significant different impedance. It could appear as bright in the US iamge.

what does Transmission do to a US Image?

when two adjacent tissues have similar impedance values. causing shades of gray of the tissue, almost indistinguishable. W

What are the pros of US scans?

• Non-ionizing & safe – no radiation, OK for pregnancy.
• Real-time visualization of motion & procedures.
• Portable / bedside – hand-held units possible.
• Low cost compared with CT /MRI.
• Multiplanar on-the-fly by tilting the probe.
• Doppler modes for flow velocity/direction.
• Good for procedure guidance; no special shielding needed.

What are the cons of US imaging?

• Operator-dependent image acquisition & reading.
• Poor through bone or gas → lungs, bowel, skull block beam.
• Lower spatial resolution than CT /MRI (esp. deep organs).
• Artifacts: speckle, shadowing, enhancement, refraction.
• Depth vs resolution trade-off (high f = shallow detail; low f = deep blur).
• Narrow field of view; large lesions can be missed.
• Degraded by obesity, dressings, overlying gas; Doppler angle-sensitive.

what are the advantages of nuclear functional imaging?

Shows function, not just anatomy → detects disease earlier (e.g., tumour metabolism, myocardial perfusion).
• Whole-body capability – one tracer, full survey for metastases.
• Quantitative – uptake values (SUV in PET) help measure therapy response.
• Fusion-ready – SPECT-/PET-CT or -MRI overlays function on high-res structure.
• Trace-level dosing – only picograms of biologic compound needed; minimal pharmacologic effect.

What are the drawbacks of nuclear imaging?

• Ionising radiation – γ-dose to patient limits repeat studies and is contraindicated in pregnancy.
• Cost & logistics – cyclotron-produced tracers (e.g., ^18F) have short half-life, require onsite radiopharmacy; PET scanners and detector rings are expensive.
• Spatial resolution – PET ≈ 4 mm; SPECT ≈ 8 mm (lower than MRI/CT).
• Acquisition time – SPECT or PET scans can take 15–30 min with patient still.
• False-positives/negatives – uptake depends on physiology (inflammation, brown-fat, blood glucose) and may obscure or mimic disease.
• Limited availability – high-end PET/MRI systems are scarce outside major centres.

What are the advantages of x-rays?

Pros • Very fast (< 1 s) • Low radiation dose • Widely available & inexpensive • Good for bones and device placement

What are the cons of x-rays?

Cons • 2-D projection—no depth, structures overlap • Limited soft-tissue contrast • Sensitive to positioning errors.

What are the advantageous with CT scans?

Pros • True cross-sections and 3-D reconstructions • Excellent delineation of bone, soft tissue, air, metal • Quantitative Hounsfield Units for density measurement • Guides precise surgery / radiotherapy planning.

What are the disadvantageous with CT images?

Cons • Higher radiation dose than single X-ray • More expensive & less portable • Longer scan and reconstruction times • Motion artifacts if patient can’t stay still.

What is planar scintigraph?

whole body scans

what is are tomographic scans?

layers of images

Single photon emission computed tomograph (SPECT)

uses single gamma ray photon emission and its mostly used with cardiac imaging. They spin

What is positron emission tomography?

it is mainly used for brain imaging and are stationary. They perform anti-parallel gamma rays to get detection on each side of the detectors.

SPECT Vs. PET

• SPECT rotates

• PET is stationary

  • PET is more expensive

• PET has higher sensitivity

• PET has better resolution

What is photelectric absorption in x-rays?

This is when an x-ray knocks out an inner electron and forces a valence electron to take its place. this releases energy because of this. This create contrast between organs. (white vs gray)

what is Compton scattering?

This is when the incoming photon knocks off a valence electron. this causes the image to have higher contrast or a blurring effect.

What is x-ray mainly used for?

• medical device evaluation

• bone fractures

• chest c-rays

• mammography

• angiography

  • fluoroscopy (real time)

What are the trends with kvp in x-ray?

• low kvp = less photon energy = less penetration = more x-rays absored by the body = higher contrast

• high kvp = more photon energy = more penetration = less easily absorbed by the body = low contrast

What are the trends witl milliamperage (mA)

• Low mA = less number of photons produced = less x rays to be absorbed = less pass through the body = less reach sensor

• High mA = more number of photons produced = more x-rays absorbed = more pass through body = more reach ir sensor

• low ma decreases patient does but high ma increase patient does

How are oxygenated cells affected by x-rays?

they are more prone to be damaged

Which produced a higher does of radiation? CT or x-rays?

CT machines produce a higher radiation does

Why do CT machines have worse resolutions than x-rays?

because the machine is spining very fast, creating noise in the signal.

what are the main steps of CT image reconstruction?

• Data acquisition – rotate X-ray source + detector around the patient, collecting hundreds of 2D projection profiles.

• Sinogram formation – arrange each line-sum (projection) by detector position t and angle θ into a 2D plot.

• Filtering – apply a “ramp” filter (high-pass) to each projection to restore edge detail lost in back-projection.

• Back-projection – smear each filtered projection back across an empty image at its original angle; overlapping streaks build up the slice.

• Stack & render – repeat for each slice, then stack axial images into a volume or produce 3D renderings.

What do foward project mean in in CT?

mathematically sums attenuation (μ) along straight rays through the object → produces the raw projection data (sinogram).

what does filtered back project mean in CT?

Reverses forward projection by:

1. Filtering each projection in the frequency domain (ramp filter) to sharpen high-frequency edges,

2. Back-projecting them at their original angles so that the overlapping filtered data reconstructs the original attenuation map (slice).