Fundamentos Imaginologia

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Fundamentos de 
Diagnóstico por 
Imagem 
Liga Acadêmica de Radiologia da 
Universidade de Itaúna 
(RADIOUIT) 
RADIOGRAFIA 
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Escala Hounsfield 
• In general, bone is +400 to +1,000 H, soft tissue is +40 to +80 H, fat is -
60 to -100 H, lung tissue is -400 to -600 H, and air is -1,000 H. 
 
Comparação de janelas 
Janela Tecidos Moles Óssea 
Largura 482 H 2.000 H 
Nível 14 H 400 H 
ARTEFATOS EM 
TC 
Artefatos 
• Artifacts are components of the image that do not faithfully reproduce 
actual anatomic structures because of distortion, addition, or deletion of 
information. Artifacts degrade the image and may cause errors in 
diagnosis. 
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Nivelamento de volume 
• Volume averaging is present in every CT image and must always be 
considered in image interpretation. The displayed two-dimensional image 
is created from data obtained and averaged from a three-dimensional 
volume of patient tissue. Slices above and below the image that is being 
interpreted must be examined for sources of volume averaging that may 
be misinterpreted as pathology. 
 
‘Endurecimento’ de feixe 
• A beam-hardening artifact results from greater attenuation of low-energy x-ray 
photons than high-energy x-ray photons as they pass through tissue. The mean 
energy of the x-ray beam is increased (the beam is hardened), resulting in less 
attenuation at the end of the beam than at its beginning. Beam-hardening errors 
are seen as areas or streaks of low density extending from structures of high x-
ray attenuation, such as the petrous bones, shoulders, and hips. 
 
 
Movimento 
• A motion artifact results when structures move to different positions 
during image acquisition. Motion occurs as a result of voluntary or 
involuntary patient movement, breathing, heartbeat, vessel pulsation, or 
peristalsis. Motion is demonstrated in the image as prominent streaks 
from high- to low-density interfaces or as blurred or duplicated images. 
Breathing motion during image acquisition duplicates the margin (arrow) of the spleen, 
simulating a subcapsular hematoma in this patient, who was imaged because of abdominal 
trauma. 
 
Estrias 
• Streak artifacts emanate from high-density sharp-edged objects, such as 
vascular clips and dental fillings. Reconstruction algorithms cannot 
handle the extreme differences in x-ray attenuation between very dense 
objects and adjacent tissue. 
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Streak Artifact. Shotgun pellets produce a severe streak artifact on this CT image. 
 
RESSONÂNCIA 
MAGNÉTICA 
• Classicamente assume-se que os 
spins precessam em torno do 
campo magnético externo e não 
estão perfeitamente alinhados 
segundo o campo magnético (a 
magnetização total e que possui a 
direção do campo) 
• A aplicação de um campo de 
radiofrequências tem como 
consequências: 
– colocar os spins em fase 
– aumentar a população 
correspondente aos spins 
antiparalelos 
• Ao sujeitar o corpo a impulsos 
de 90o (ou outros) a 
magnetização total passa a ter 
uma componente transversal e 
é esta que é medida através de 
bobinas transversais. 
• Com o tempo, o sinal decai. 
Desfasagem 
Dos spins 
 
 
Magnetização 
Transversal 
 
 
Sinal medido 
(FID) 
Parâmetros usados - Ponderações 
T1 
• Medida da capacidade dos 
prótons de trocar energia com 
a matriz química circundante, 
ou seja, medida de quão 
rapidamente o tecido é 
magnetizado. 
T2 
• Medida de quão rapidamente 
um determinado tecido perde 
sua magnetização. 
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ARTEFATOS EM 
RM 
Susceptibilidade Magnética 
• A magnetic susceptibility artifact is caused by focal distortions in the main 
magnetic field resulting from the presence of ferromagnetic objects such as 
orthopaedic devices, surgical clips and wire, dentures, and metallic foreign 
bodies in the patient. The artifact is seen as areas of signal void at the location of 
the metal implant , often with a rim of increased intensity and a distortion of the 
image in the vicinity. 
• Magnetic Susceptibility Artifact. Radiograph of the pelvis (A) and axial plane T2WI 
(B) in the same patient show the artifact (white arrow, white arrowhead) produced by 
metallic clips (black arrows) used for tubal ligation. The dramatic increase in artifact 
on the right side (white arrow) as compared to the left side (white arrowhead) is 
caused by proximity of the right-sided clip to a blood vessel, which created a 
pulsatile motion of the clip. 
Movimento 
• Motion artifacts are common in MR because of the long image acquisition time. 
Random motion produces blurring of the image. Periodic motion, such as that 
caused by pulsating blood vessels, causes ghosts of the moving structures. 
Motion artifacts are most visible along the phase-encoded direction. Swapping 
phase- and frequency-encoded directions may make the artifacts less bothersome. 
 
 
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• Pulsations of the aorta 
(arrow) produce 
numerous ghosts of the 
aorta in the phase-
encoded direction. 
Swapping the phase-
encoded direction with 
the frequency-encoded 
direction will enable 
evaluation of the left 
lobe of the liver. 
 
Erro de registro de desvio químico 
• Chemical shift misregistration occurs at interfaces between fat and water. Protons 
bound in lipid molecules experience a slightly lower magnetic influence than protons 
in water when exposed to an externally applied gradient magnetic field, resulting in 
misregistration of signal location. The artifact is seen as a line of high signal intensity 
on one side of the fat-water interface and a line of signal void at the opposite side of 
the fat-water interface. Evaluation of the bladder wall and renal margins is difficult in 
the presence of this artifact. 
 
• Chemical shift 
misregistration between 
fat and kidney tissue 
produces a high-density 
band (short arrow) on 
the medial aspect of the 
left kidney and a low-
density band (long 
arrow) on its lateral 
aspect. 
Truncagem 
• Truncation errors occur adjacent to sharp boundaries between tissues of 
markedly different contrast. This artifact is attributable to inherent errors 
in the Fourier transform technique of image reconstruction. The artifact 
appears as regularly spaced, alternating, parallel bands of bright and dark 
signal. 
Aliasing ou Revestimento 
• Aliasing, or an image wraparound artifact, occurs when anatomy outside the 
designated field of view but within the image plane is mismapped onto the 
opposite side of the image, for instance, on a midline sagittal brain MR, the 
patient's nose may be artifactually displayed over the area of the posterior fossa. 
Aliasing may be eliminated by increasing the field of view (at the expense of loss 
of image resolution) or by increasing the number of phase-encoding steps outside 
the field of view (oversampling). ULTRASSONOGR
AFIA 
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The US transducer transmits a brief pulse of US energy into tissue. The transmitted 
US pulse encounters tissue interfaces that reflect a portion of the US beam back to 
the transducer. The depth of the tissue interface is determined by the round trip time 
of flight for the transmitted pulse and the returning echo, assuming an average speed 
of 1,540 m/s for sound transmission in human tissue. 
Setoriais: campo de visão mais amplo no campo 
mais longe 
Lineares: campo de visão mais amplo no campo 
mais próximo 
ARTEFATOS EM 
US 
Sombra acústica 
• Acoustic shadowing is produced by nearly complete absorption or 
reflectionof the US beam, obscuring deeper tissue structures. Acoustic 
shadows are produced by gallstones), urinary tract stones, bone, metallic 
objects, and gas bubbles. The presence of acoustic shadowing aids in the 
identification of all types of calculi. 
 
• A gallstone (cálculo biliar) within the 
gallbladder produces a dark acoustic 
shadow (arrows) by absorption of the 
US beam. Demonstration of acoustic 
shadowing is important in the US 
detection of biliary and renal calculi. 
Realce acústico 
 
• Acoustic enhancement refers to the increased intensity of echoes deep to 
structures that transmit sound exceptionally well, such as cysts, fluid-
filled bladder and gallbladder, and some solid masses, such as 
lymphoma-replaced lymph nodes. The presence of acoustic enhancement 
aids in the identification of cystic masses. 
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• US image of a cyst (C) in the 
liver demonstrates acoustic 
enhancement (arrows) as a 
band of bright echoes deep to 
the cyst. 
 
Reverberação 
• Reverberation artifacts are caused by repeated reflections between strong 
acoustic reflectors. Returning echoes are re-reflected into tissues, 
producing multiple echoes of the same structures that are portrayed on 
the image progressively deeper in tissue because of the prolonged time of 
flight of echoes that eventually return to the transducer. A reverberation 
artifact is seen as repeating bands of echoes of progressively decreasing 
intensity at regularly spaced intervals. 
Imagem espelhada 
• Mirror-image artifacts are common when examining the upper abdomen 
and diaphragm. Multipath reflection from the strong sound reflection 
produced by the air-filled lung surface above the curving diaphragm 
results in depiction of liver or spleen tissue patterns both below and 
above the diaphragm. 
 
 
• Longitudinal image of the left 
upper quadrant of the abdomen 
demonstrates the spleen (S), 
diaphragm (arrow), and 
artifactual mirror image (MI) 
of the spleen above the 
diaphragm. K, left kidney. 
 
• The ring down, or comet tail, artifact is seen as a pattern of tapering 
bright echoes trailing from small bright reflectors such as air bubbles and 
cholesterol crystals. The artifact may be the result of vibrations of the 
reflector or of multiple short-path reverberations. 
Ultrasound of a 40 year old 
female demonstrates 
numerous ring down 
artefacts (comet tail 
artifact) from the 
gallbladder (vesícula biliar) 
wall consistent with 
adenomyomatosis. 
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CONTRASTES 
Constrastes 
• Realçam as diferenças na densidade entre as lesões e o parênquima 
circundante. 
Constrastes em TC 
• Ionic Contrast Agents (high osmolality contrast agents) - anel de 
benzeno e iodo; dissociam-se. Hipertônicos em relação ao plasma. 
• Nonionic Contrast Agents (low osmolality contrast agents) – monômeros 
não iônicos. Osmolaridade reduzida acarreta menos efeitos 
hemodinâmicos. 
Constrastes em RM 
• Gadolinium Chelates 
• Inclui compostos iônicos e não iônicos. 
• O efeito paramagnético reduz T1 e T2, geralmente encurtando mais T1. 
• As concentrações normais de gadolíneo são melhor visualizadas em 
T1WI. 
• Entretanto, concentrações teciduais muito elevadas (rins), podem 
provocar uma redução considerável de sinal, melhor visualizável em 
T2WI. 
Constrastes GI 
• Barium Sulfate 
– Estudos duplo contrastados: Ar ou Metil-celulose 
• Gas Agents 
• Water-Soluble Iodinated Contrast Media 
 
Contrastes em US 
• The microbubbles interact with the imaging technique, oscillate at a 
resonant frequency, and can be made to abruptly disrupt to improve the 
signal from the contrast agent. Imaging is performed in arterial and 
venous phases. Contrast washout or sustained enhancement of lesions 
can be assessed. 
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CONSIDERAÇÕE
S SOBRE DOSES 
DE RADIAÇÃO 
Dose absorvida (D) 
• Exposição refere-se à ionização de partículas, não sendo adequada para 
analisar efeitos em tecidos. 
• Define-se como dose (D) a energia da radiação absorvida pela massa do 
absorvedor, ou seja, D = E/m. 
• A unidade padrão é o gray (GY), que corresponde a 100 rad. 
• 1 GY = 1 J/kg 
Referências 
• BRANT, William E.; HELMS, Clyde A. (Ed.). Fundamentals of 
diagnostic radiology. Lippincott Williams & Wilkins, 2012. 
• CAMERON, J. R. & SKOFRONICK, J. G. Medical Physics. NY: John 
Wiley & Sons, 1978. 
• JUHL, John H.; CRUMMY, Andew B.; KUHLMAN, Janet E. 
Interpretação radiológica. Interpretação radiológica, 2000. 
• OKUNO, Emico; CALDAS, Iberê Luiz; CHOW, Cecil. Física para 
ciências biológicas e biomédicas. São Paulo: HARBRA, 1986. 490 p. 
 
 
• BARRETT, Julia F.; KEAT, Nicholas. Artifacts in CT: Recognition and 
avoidance1. Radiographics, v. 24, n. 6, p. 1679-1691, 2004.