Rotational Panoramic Radiography

Seung - Hyun Heo

Radiography

IN Horizontal Dimension

- Rotation center of the beam

>> Serves as the functional focus.

IN Vertical Dimension

- X-Ray Source>> Serves as the functional focus.: Just as a conventional radiographic projection.

IntraOral v.s. ExtraOral ExtraOral Radiography

- Panoramic Radiography ,Tomography- Show the entire dentition and related structures on a single film.- The patient in a seated position, and other types require the patient to be

in a standing position.- Regardless of the type of machine, Must follow the manufacture`sinstructions carefully

- Panoramic film are not as clear or as well defined as the images on IntraOral films

Panorama- “ an unobstructed view of a region in any direction”- The series of images are combined onto a single film, an

overall view(panorama) of the maxilla and mandible is created.

- 구내방사선사진들에비하여촬영이간단 .- 방사선노출량이적고 , 개구제한이있는환자에도사용가능 .- 구내방사선사진에비하여해상도가떨어지며 , 소구치부의인접면중첩현상이있다 .- 확대율이일정하지않으며기하학적왜곡이발생한다 .

Conventional CT vs ConeBeam CT

Conventional CT CBCT(ConeBeam CT)

영상형성에적용되는기본적인원리유사 . 차이점 - Conventional CT : 선형원형검출기를사용 , 각검출기에입력되는정보를 바탕으로 2 차원의단면 상을형성한다 . - CBCT : 원뿔형태의 X 선을투과하는피사체의투과감쇠를 2 차원적인평면을검출 , 이를 Filtered back projection 하는수학적알고리즘을적용하여 3 차원체적의정보를획득하고 , 이로부터이차원 단면상획득 >> 다면영상재구성시상의외곡이없이모든방향에서의정확한영상획득 .

Conventional CT vs ConeBeam CT

Voxel(체적소 )

Process of Image reconstruction.

Detector 영상증배관및 CCD Sensor 사용방식 .

비결정실리콘 (amorphous Silicon , a-Si) 소자를배열한박막필름트랜지스터 (thin-film transistors, TFTs) 를사용하는 flat-panel detector.

CBCT 방식은상대적으로낮은 조사선량으로진단적가치있는영 상의획득가능하다 . 기존의파노라마촬영술이나구내 촬영술에비하여많은피폭선량 .

CBCT 영상의학적고려사항 (1) 양자화시 Bit depth

- 양자화과정 : 아날로그신호를디지털신호로변환- 클수록질좋은영상획득 .

공간분해능 (Spatial resolution)

- Voxel size 가증가함에따라공간 분해능은감소 .

계조분해능 , 농도분해능 (Contrast resolution)

- 영향을주는요인 : bit depth, 산란방사선에의한신호잡음의비 .- CBCT 는원뿔형 X 선속과 2 차원적인평면검출기사용 : 4~5 배의산란방사선 .

CBCT 영상의학적고려사항 (2) 영상인공음영 (artifact)

- 기존의 conventional CT 에서는금속체주위로햇살모양의 Sun burst artfact 형태로발현 .- CBCT 영상은금속체의근원심면이검게보이고 , 협설측에서보다하얗게 나타나는현상발생 .

Window width/level(contrast/brightness)

- X 선에대해감약이적은조직 (공기 , 지방 ) 은검게보이고 , 감약이큰골조직에서는 밝게나타난다 .

Focal trough : 상층 파노라마방사선사진상에구조물이

명확하게나타나는입체적곡면 .

- An imaginary, 3D curved area that ishorseshoe shaped

- When the jaws are positioned outsideof this area, the images on the radiographwill appear blurred or indistinct.

Component of a panoramic unit Panoramic x-ray tubehead

Component of a panoramic unit Head Positioner

- Align the patient`s teeth as accurately as possible.- Consist of a chin rest, notched bite-block, forehead rest,

and lateral head supports or guides.