CT Scans (CT Scanning)

CT Scan Picture

Computed tomography (CT) or Computed Axial Tomography (CAT) is imaging tools use X-rays to make detailed pictures of structures inside of the body. This medical imaging method employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object.

CT scanning was developed during the mid-1970s, a CT scanner emits a series of narrow beams through the human body as it moves through an arc, unlike an X-ray machine which sends just one radiation beam. The CT machine takes pictures of your body from different angles and gives a series of cross sections or 'slices' through the part of the body being scanned and often result in earlier diagnosis and more successful treatment of many diseases. X-rays are high energy photons (the energy "packets" of electromagnetic energy, similar to light but not in a visible wavelength) similar to gamma rays that pass through the body. More dense tissues such as bone block most x-rays while softer tissues let more x-rays pass completely through. Therefore, the image produced by an x-ray and CT scan is based on the density of tissues. Bones show up brightest while air is the darkest, this will make very detailed picture of the inside of the body can be built up in this way. In some CT scans, contrast agents or sedatives (iodine) may be used.

A CT machine resembles a large, square doughnut. A flat "patient couch" is situated in the circular opening, which is about 24 to 28 inches in diameter. The patient lies on the couch, which can be moved up, down, forward, and backward to position the patient for imaging. The CT scanner itself is a circular, rotating frame with an x-ray tube mounted on one side and a banana-shaped detector mounted on the other. A fan-shaped beam of x-rays is created as the rotating frame spins the x-ray tube and detector around the patient. For each complete rotation, one cross-sectional slice of the body is acquired. As the scanner rotates, the detector takes numerous snapshots called "profiles." Typically, about 1,000 profiles are taken in one rotation. Each profile is analyzed by computer, and the full set of profiles from each rotation is compiled into to form the slice-a two-dimensional image. The accuracy and speed of CT scans may be improved with the application of spiral CT. Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called "multislice CT" or "multidetector CT. The X-ray beam takes a spiral path during the scanning - it gathers continuous data with no gaps between images.

Risks of CT scans include:

• Being excessive exposure to radiation
• Allergic reaction to contrast dye (iodine)
• Not recommended for pregnant women and nursing mothers

CT Scans Benefits

• CT scanning is painless, noninvasive and accurate.
• CT examinations are fast and simple, about 30 minutes to complete

PET Scans (Positron Emission Tomography)

Positron Emission Tomography (PET) scan is a nuclear/radiation medicine modality, which was first introduced by Brownell and Sweet in 1953. The prototype has been built in about 1952. Positron Emission Tomography  was first developed by Massachusetts General Hospital, Boston in 1970. Positron which is the core of PET Scans was first introduced by PAM Dirac in 1920. PET Scans is a visualizing method of body's metabolism using positron-emitting radioisotopes. Therefore, image which obtained from PET Scans was an image that describes the function of organs. The main functions of PET is to know cellular activities that may not obtained with other conventional imaging tools, so with PET Scans the abnormalities metabolism in the body can be determined by imaging methods. This is different from other body visualization methods such as x-rays, computed tomography (CT), magnetic resonance imaging (MRI) and single photon emission computerized tomography (SPECT). 

CT Scan and MRI can detect cancers limited to the anatomy. For example, CT scans and MRIs are only able detecting breast cancer, head, liver, etc but unable describe the organs metabolism, with the PET-Scan, anatomical, metabolic aspects, and spread of cancer are also detected. Furthermore PET Scans detection capability include cancer type, degree of malignancy, locations, and ways of propagation of this deadly disease. 

PET also can be use  to analyze the results of cancer treatment that has been done. After the treatment of cancer through surgery, it is necessary to check whether there was still some residual cancer remains. For this purpose, PET is the most appropriate method, because in these conditions (after sugery) the presence of cancer is difficult to see physically. In addition, PET also can be used to view the progress of cancer treatment with chemotherapy or radiotherapy or other cancer treatment method that may be has been done. Progress of cancer treatment outcome can be known from metabolic changes in addition to physical changes. For this purpose, the combination of PET and CT provides very valuable  information to determine the treatment effectiveness  level that has been done.

PET Scans Mechanism
Cancer cells have higher metabolic rates than other cells. One cancer cells characteristic is cancer cells require higher levels of glucose for energy. Positron emission tomography build 3D images of glucose metabolism in cancer cells by detecting gamma rays emitted when radioactive glucose is injected into a  patient body. Once ingested, the sugar is absorbed by the tissue was processed with a higher level of activity / metabolic (eg, active tumor).

PET-scan begins by giving an injection of FDG (a radionuclide glucose-based) from the syringe into the patient. As FDG travels through the patient's body that emits gamma radiation, the FDG  detected by a gamma camera, from which the chemical activity in cells and organs can be seen. Any abnormal chemical activity that may be sign is the indicator of tumor present.
Gamma rays are produced when a positron emitted from radioactive material collides with electrons in the organ. The resulting collision produces a pair gamma ray photons that coming from the collision site in the opposite direction and detected by gamma ray detectors that placed around the patient.  PET detector consists thousands scintillation crystals and hundreds photomultiplier tubes (PMTs) arranged in a circular pattern around the patient. Scintillation crystal is used to converts gamma radiation into light and amplified by the PMTs.  The low noise amplitudo (LNA) convert the signals from PMTs into voltage and amplitude. PMT signal generated by a signal pulse is slow. The signal strength from each PMT is determined by integrating the signal into pulses. After the LNA, the system uses a variable-gain amplifier (VGA) to compensate for variability in the sensitivity of the PMTs. 

The output from VGA passed through a lowpass filter, offset compensation, and then converted into digital signals in 10 to 12-bit analog-to-digital (ADC converter sampling) with 50Msps to assess 100Msps.
Every signals from each PMT will be added to get ultra high speed signal. A DAC generates a voltage reference comparator to compensate for DC offset. Very high accuracy required to produce a comparator output signal with high-speed time. The output signal from DAC is processed into image processing.
From the results of detection, image reconstruction done to get a picture of the distribution of glucose in the body. PET camera device usually comes with the program for this purpose, so that the image reconstruction can be obtained easily. 

PET Scans Camera
PET cameras have better image clarity than the gamma camera, This is because the detection is based on coincidence detection.  When a positron is released from the fluorine-18, these particles will soon join the annihilation of electrons.. This annihilation radiation from electromagnetic waves generated by 511 V in the opposite direction (180 degree). Two protons released simultaneously makes it possible to do coincidence detection. On coincidence detection, the signal that captured by the detector will be processed if two signals acquired simultaneously. If there is only one signal captured, then the signal is considered as impurities. Therefore, almost all signals of impurities can be eliminated in this way.

PET Scan Limitations
The biggest limitation of PET studies is limited availability of radioligands. Being developed more than 60 years ago, and immersed to the clinical environment during the past 20 years based only by studies of glucose metabolism, it will take a lot of efforts to simplify and standardize radiopharmaceutical production methods to introduce new radioligands with competitive prices for the needs of PET imaging. In addition, since PET isotopes are short-lived, they have to be processed near the imaging facility.

Complete Information Of Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) is an imaging technique using strength magnets, the interaction of high strength magnets and Radio Frequency transmissions with body tissues. MRI has been used for decades to largely evaluate the brain, spine, and musculoskeletal system and become standard modality in medical settings throughout the world as it provides anatomic and physiologic information noninvasively and without the use of ionizing radiation.  MRI will allow to provide more detail, faster, with no damaging effects to patients. As an imaging modality that offers tissue differentiation without harm to patients, the imaging that magnetic resonance offers has rapidly developed into the physician’s modality of choice. MRI first performed on a human in 1977

Unlike nuclear medicine or CT imaging that use radioactivity or X-rays, MRI use high strength magnetic field. The largest part of an MRI unit is the superconducting magnet with 10,000g equals  to 1 T. The MRI magnet is used to align the atoms and depends on properties of the nucleus.  MRI scanners use the element hydrogen, with its single proton in the nucleus and abundance in all tissues of the body, to generate a strong signal. These protons spin, generating a magnetic field, with north and south poles on the axis of their spin. In the body, these protons are arranged in random directions, similar to iron atoms in a piece of soft iron.

Magnetic Resonance Imaging is widely used to detecting breast cancer include staging known breast cancer, monitoring the response to cancer treatment, checking if a breast cancer has come back after treatment, evaluating the breasts in a patient with cancer in the lymph nodes of the armpit who has a mammogram that does not show breast cancer, checking for rupture of breast implants, and screening for breast cancer in high-risk patients (those with BRCA-1 and BRCA-2 genes - genetic markers for an increased risk of breast cancer).

If a patient undergoes MRI (typically takes between 30 and 60 minutes to complete), the facility performing the examination should use, at a minimum, a dedicated breast coil, a high field magnet greater than 1 Tesla (a measure of strength of the MRI), offer high spatial and temporal resolution, and be able to subtract fat signal from the images.

MRI cannot be performed on certain people. For example, having a pacemaker, certain types of surgical clips, metal pins or plate. These issues aside, MRI of the breasts is now possible and there are many indications for such an examination. In the future, we will likely see an even greater role for MRI of the breasts that will hopefully enable us to provide even better healthcare and earlier detection of breast cancer. Magnetic Resonance Imaging (MRI) generally cost around £200 to £600.