Echo Train Length

Allocate required phase lines into bounded echo trains, retaining a short final shot; echo weighting, k-space ordering and sequence-specific ETL definitions are external.

Description

An echo-train allocation splits required phase lines into shots with a maximum number of echoes per shot.

An echo-train allocation splits required phase lines into shots with a maximum number of echoes per shot. The last shot may be shorter.

The tool returns shotEchoCounts (shot echo counts); shotCount (shot count). Input measurements and model parameters are supplied by the caller; the tool computes the stated summary rather than acquiring those measurements.

When to use Echo Train Length

Use Echo Train Length when you already have requiredPhaseLines, maximumEchoesPerShot and want shotEchoCounts, shotCount. This is useful for checking a supplied calculation, documenting a measurement convention, or comparing observations prepared on the same basis.

How to use Echo Train Length and understand its results

Enter requiredPhaseLines, maximumEchoesPerShot using the field table below. Match the units, ordering and data boundaries described in the calculation.
Run the tool after checking the stated bounds and matching paired observations or categories. A malformed request gives a tool error rather than a usable measurement.
Read shotEchoCounts, shotCount. Use the calculation and interpretation below to distinguish amounts, ratios, signs and decision flags where applicable.
Review the supplied parameters and assumptions before using the result in a report or comparing it with another observation.

Input field	Meaning	Value type and bounds	Requirement
requiredPhaseLines	Required phase lines	integer	Required
maximumEchoesPerShot	Maximum echoes per shot	integer	Required

Use positive integer counts and a bounded resulting shot count. Allocate full shots before the final remainder.

shotCount = ceil(requiredLines/maxEchoes); shot[i] = min(maxEchoes,remainingLines)

The symbols refer to the supplied quantities or generated values described above; unit conversions and comparison boundaries follow the stated implementation.

json

{
  "input": {
    "requiredPhaseLines": 130,
    "maximumEchoesPerShot": 32
  },
  "output": {
    "shotEchoCounts": [
      32,
      32,
      32,
      32,
      2
    ],
    "shotCount": 5
  }
}

Limitations and assumptions

No ordering, contrast evolution, echo spacing or scan-time overhead is calculated.

Numerical inputs must be finite. The tool checks its declared input shape and calculation constraints; those checks do not verify the quality, calibration or representativeness of the supplied observations.

Alternative or Complementary methods

Repetition Time TR: Budget sequential nonoverlapping slice blocks plus recovery time within TR; simultaneous or interleaved waveform schedules are not inferred. GRAPPA Acceleration: Count unique regularly subsampled phase lines plus a contiguous ACS interval, avoiding double counting; GRAPPA kernel fitting and reconstruction are not performed.

Methodological background: RAD229: MRI signal and sequence lecture notes.^[1]

References

RAD229: MRI signal and sequence lecture notes — Brian Hargreaves and colleagues, Stanford University

Similar or alternative tools

Repetition Time TR
Budget sequential nonoverlapping slice blocks plus recovery time within TR; simultaneous or interleaved waveform schedules are not inferred.
GRAPPA Acceleration
Count unique regularly subsampled phase lines plus a contiguous ACS interval, avoiding double counting; GRAPPA kernel fitting and reconstruction are not performed.