CT Seeram: Components of a CT Scanner

Major Components Scanner room Imaging system Generator (?) Electronics Room Power Computer (?) Generator (?) Operator’s Area Display / recording / storage Computer (?)

Gantry Provides Structural Framework for x-ray tube modern tubes very large & heavy external cooling (oil heat exchanger) generator / transformer (slip ring technology) Extreme mechanical stability requirements Very tight tolerances for vibration Give / sag

Gantry Provides Structural Framework for collimators filters Detectors / electronics

Gantry Size Must Accommodate patients size of room Truck transport to hospital The gantry is pre-assembled at the factory

Gantry Size Must Accommodate Transport within hospital hallways doors elevators Typical weight: 3500 lb.

Special Clinical Gantry Concerns Patient aperture Tilt range Cooling of electrical components x-ray tube

Patient Couch Vertical travel minimum height for stretcher transfer Horizontal travel reduces need for re-positioning patient accuracy

Patient Couch Weight capacity Strength cantilevered Rigidity

Patient Couch Requirements Safe for patients Easy to clean Radiolucency Speed Pretty? Siemens offers colors

Imaging System Produces x-rays Shapes & filters (hardens) beam collimates attenuates for uniformity May detect (measure) pre-patient beam intensity Provides digital intensity data to computer

Imaging System Components X-ray tube Generator supplies power to x-ray tube filament high voltage Collimators restricts beam to slice of interest

Imaging System Components Filter protects patient from low-energy photons provides a beam closer to mono-energetic provides a more uniform beam Detector & electronics also called data acquisition system (DAS) includes A-D converter provides digital information to reconstruction computer

Computer System Components Input / output devices Detectors Printer Central processing units (CPU’s) Array Processor Reconstruction Hardware u Interfaces to other computers Remote service RIS Archive Web browser u Communications hardware u Software enables above hardware operation image manipulation scanning control

Reconstruction Computer Receives digital data from DAS Reconstructs cross-sectional image Image display, manipulation, & processing windowing enhancement zoom quantitative measurements multi-planar & 3D reconstruction

Image Display, Record, Storage Display output image Facilitate storage / retrieval of digital data Provide permanent hard-copy for referring physician (?)

Computer & Image Processing Hardware Special processing architecture Software

Processing Architecture Multi-processing capability scanning reconstructing archiving Distributed processing architecture many independent processors each controls specific function

CT Software Functions Operator console Allows operator to communicate with computer & scanner keyboard touch screen mouse / trackball u Control of scanner Gantry tilt scout / axial field of view x-ray technique slices »how many »thickness »overlap

CT Software Functions Control of imaging selection of pre-stored image protocols Selection of reconstruction algorithm Operating System often UNIX multiuser multitasking controls hardware

Image Display, Storage, & Recording Display CRT or flat panel images in gray shade non-image data in color or B/W often hi-resolution Can display 4-on-1 or zoomed image at full resolution Display processor provides display functions image manipulation

Image Storage Typical CT image 512 X 512 pixels 8-12 bits deep often stored as 2 bytes / pixel (16 bits / pixel) Multiply image size by # images

Image Size 512 X 512 image = 262,144 pixels 262,144 pixels X 2 bytes / pixel = 524,288 bytes per image ~ 512 KB ~ 0.5 MB

Image Storage (cont.) Assume 0.5 Mbytes per image If 100 images / patient 50 Mbytes / patient 25 patients / day X 50 MBytes / patient = 1.25 GBytes per day

High Capacity Image Storage Magnetic disk Magnetic tape Digital videotape Optical disks Optical Tape u Capacity u Access Speed u Rewritable? u Size / space u Longevity u On line? u $$$ TypesConsiderations

CT Hard Copy on Laser Printer Stringent quality requirements broad gray- scale contrast resolution high spatial resolution No film processor required

CT Hard Copy on Laser Printer Requires special film Film’s spectral sensitivity must match laser Laser types solid state gas (He-Ne)

Laser Printing Film exposed by scanning line by line with laser

Laser Printer Features Contains image buffer (computer memory) Buffer stores images in memory until printed Camera prints multiple images on one film Camera can receive & buffer multiple image sources images simultaneously

CT Console Keyboard Mouse Display CRT Flat panel Touch panel

CT Console Allows Operator to Control Gantry tilt scanning parameters Slice thickness Spacing Technique image manipulation multiplanar reformatting 3D zoom / pan

CT Available Automatic Control Functions Archiving Voice instruction to patient Visual instructions to patient Auto-film protocols (?) Window / level Format (12 on 1 for example)

Optional Purchases CT Hardware Archival systems Independent workstations Physicians 3D Printing Laser Multi-format

CT Options Bone mineral analysis Dynamic scan rapid sequential scans of single slice Multiplanar reformatting 3D image reconstruction Regional cerebral blood flow analysis CT Angiography Dental CT (surgery planning, implants) Networking

CT Room Layout Gantry Couch Room for Resuscitation team Emergency equipment Stretchers Medical Gasses Shielding

CT Room Layout Equipment room not always necessary as scanners become smaller Control room Film recording may be combined with control room

Purchasing CT; Specifications List of Items Major components Optional equipment Major technical features should be measurable

CT Specifications Who’s Involved? Radiologist Technologist Physicist Administrators

Technical Specifications X-ray generator parameters operational parameters maximum kVp kW rating u X-ray tube heat capacity cooling rates u Detector efficiency u Reconstruction time u Throughput

CT Specifications Gantry aperture size tilt range laser positioning aids controls Couch strength / weight limits movement characteristics Speed Limits

CT Specifications; Operator’s Console Display, keyboard, mouse, touch panel characteristics Software design Choice box of available options vs. manual typing Film recording & archival considerations

CT Specifications Physician’s console & other workstations functions available speed Simultaneity Computer storage requirements CPU networking

CT Specifications Interfaces PACS hooks & DICOM compatibility Worklist management Pulling patient demographics from RIS Image storage Transfer of images to archive / PACS

Computer Software CT Specifications image reconstruction options FOV filters display options annotation analysis options regions of interest

CT Specifications Hardcopy devices & interface laser printer Quality control equipment phantoms software Remote Diagnostics

CT Specifications Acceptance Testing Who performs What tests done Technology Changes “Latest model available at time of delivery” Service Warranty Binding service contract prices

Purchasing CT Room planning in consultation with equipment vendor Property ownership. Who owns? And when does ownership transfer? service manuals diagnostic software operating system Property ownership dictates hidden software costs & service options

CT Specifications: Training For whom? Technologists How many? Where? Vendor site On-site Local What’s included Registration Books Travel expenses