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CT Imaging
Jermendy Ádám, Lénárd Zsuzsanna, Magyar Péter
Semmelweis University, Dpt. Medical Imaging
• use of X-rays
• attenuation coefficients
What does CT measure? DENSITY
Structure of a CT machineX-ray source detector panel
table is performing longitudinal movement, with the patient lying on it.
Helical scanning:Table movement and imaging is simultaneous.Higher radiation dose.
Sequential scanning:An axial slice is made and then the table moves.
lung HRCT, head CT, intervention applicationsProspective ECG gating at cardio CT
The majority of CT examination
MultiSlice Computer Tomography
multiple slices simultaneously.Better spatial and temporal resolution, lower radiation dose
The Present I.: 256- and 320-detector-row MSCT
In 256- and 320-detector row CT, the entire heart is imaged with temporal uniformity (ie. at the same time point without temporal delay from the base to apex).
It is able to scan an entire heart in one gantry rotation of 300 ms.
High-Risk Plaque Regression and Stabilization: Hybrid Noninvasive Morphological and Hemodynamic Assessment.Giannopoulos AA, Mitsouras D, Bartykowszki A, Merkely B, Chatzizisis YS, Buechel RR, Kaufmann PA, GaemperliO, Maurovich-Horvat P.
The Present II.: Dual-source CTallows differentiation of materials and tissues based on CT density values derived from two synchronous CT acquisitions at different tube potentials (140 kVp and 80 kVp, usually)
image is created based on two different attenuation datasets
can now be used routinely in abdominal imaging
provides evaluation of e.g. renal masses, liver lesions, urinary calculi, small bowel, pancreas, and adrenal glands
allows differentiation of contrast agent from calcifying thrombus in patients with endovascular stents
Graser et al., Dual energy CT: Preliminary observations and potential clinical applications in the abdomen. European Radiology 2008, 19(1):13-23
140 kVp
80 kVp
What is white on CT image? What is dark on CT image?
electron-dense structures, such as metal and bone, stop a large number of x-rays and therefore are bright on computed tomography (CT)
hyperdens
lower electron-density regions, such as air or fat, stop very few x-rays and are rendered as dark
hypodens
Large hard candy. Contrast-enhanced axial CT demonstrates a perfectly round, attenuated mass in the left lower gingivo-buccal sulcus. MecDermott et al, American Journal of Neuroradiology September 2008, 29 (8) 1552-1555;
The Hounsfield-units (HU)
• The attenuation coefficient
Hounsfield-units
water
grey scale.
Windowing (postprocessing)
window
level width
level: -600, width: 1500level: 400, width: 1800level: 50, width: 400
www.radiopaedia.org
CT Contrast Agents I: intravenous administration
Noncontrast CT : foreign bodykidney stonelung HRCT / interstitialis pulm. diseaseto exclude hemorrhage in strokeadrenal gland adenomabone structure (e.g. in trauma)fat/ lipoma / steatosisatherosclerosis (e.g. calcium score)
Contrast-enhanced CT : angiographyto study vascularization (e.g. ischemia, infarction)tumor differentiationinflammatory processes, abscesses
noncontrast phase
www.radiologyassistant.nl: CT contrast injections and protocols
www.radiologyassistant.nl: CT contrast injections and protocols
early arterial phase
www.radiologyassistant.nl: CT contrast injections and protocols
late arterial phase
www.radiologyassistant.nl: CT contrast injections and protocols
hepatic phase
www.radiologyassistant.nl: CT contrast injections and protocols
nephrogenic phase
www.radiologyassistant.nl: CT contrast injections and protocols
late phase
artériás, 15-20 sec
vénás, 70-80 sec késői, 3-10 min
natív
CT Contrast Agents I: intravenous administration
iodinated
non-contrast images: e.g.
orally or at given cases e.g. directly into fistulas
contrast material leaked from the small bowel into the laparotomy wound
CT Contrast Agents II: oral administration
jódtartalmú kontrasztanyagoknak nefrotoxikus hatása van
Post-contrast acute kidney injury (PC-AKI):
(GFR) < 30 ml/min/1.73 m2
kidney function GFR > 30 GFR < 30
ESUR guidelines 10.0 – renal adverse reaction
Role of GFR Emergency situation:
Non-vital indication:
ESUR guidelines 10.0 – non-renal adverse reactionsacute: allergic reactions from mild urticaria to anaphylactic schock
patients at risk: pusage of high-osmolality ionic contrast media
late: skin reactions, headache
very late: thyreotoxicosis patients at risk:
miscallenous:
iodine- based contrast media may be given to the pregnant female
breast feeding may be continued normally
pheochromocytoma and paraganglioma
Note: allergic reaktions to iodine basedsuperficial antiseptics are NOT equal tocontrast allergies.
Metformin, a medicine in type II diabetes
danger for lactate acidosis
patients with impaired renal function are at risk
patients with an eGFR above 45 ml/min/1.73 m2 can continue to take Metformin normally
patients with an eGFR below 45 ml/min/1.73 m2should stop Metformin 48 h before contrast administration
patients with an eGFR below 30 ml/min/1.73 m2 contrast media should be avoided
in emergency patients Metformin should be stopped and after contrast administration the patient should be carefully monitored for the signs of lactate acidosis
Emergency exam (vital indication):
• Consider an alternative imaging method not using iodine-based contrast media.
• Start volume expansion as early as possible before contrast medium administration (see elective examination).
CT can be used in a wide variety• Acute abdominal and chest diseases• Acute cerebral diseases• Oncology imaging, staging exams• Lung disease assessment (HRCT)• CT angiography (CTA)• Traumatology• Cardio CT• Gastrointestinal exams• ...
H R CT
Fields:
csontablak
csontablak
tüdőablak
acute chronic
50-80 HU 0 HU
larger hematomas can be detected on noncontrast CT
small punctuate bleeding can be depicted on MR with higher sensitivity
dense, metal foreign bodies can be detected on noncontrast CT
MR is contraindicated in this clinical situation
density: approx. 1550 HU
bowel infarction, no enhancement
abrupt filling defect in mesenteric superior artery on CT angiography
cyst no enhancement renal cell carcinoma intensive enhancement
sclerotic plaquesNormal coronary
retrospective ECG gating:
prospective ECG gating:
CT enteroclysis / enterography
Indications:
negative oral contrast agent
CT-colonography / virtual colonoscopy – colon carcinoma
Indications:
Pelvic Imaging?MRI is superior to CT in both male and female pelvic soft tissue imaging
axial T2w MRI axial noncontrast CT
Strengths and Weaknesses of CT
high ionizing dose
high cost of equipment
imaging in axial plane (with sagittal and
coronal reconstructions)
its soft tissue resolution is inferior to MRI’s
bony arterfacts (e.g. posterior fossa)
primarily axial images
contraindications (contrast allergy, kidney
failure, pregnancy, youngsters)
3D imaging
tissues are not superimposed, not magnified
good spatial resolution
good soft tissue resolution (primarily after iv.
contrast administration)
usually available
rapid imaging (more regions in some minutes)
can image calcified plaques, small kidney
stones, foreign bodies, bone fragments
can image lung tissue